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				6	<title>CommandLine 2.0 Library Manual</title>
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				10
				11	<div class="doc_title">
				12	CommandLine 2.0 Library Manual
				13	</div>
				14
				15	<ol>
				16	<li><a href="#introduction">Introduction</a></li>
				17
				18	<li><a href="#quickstart">Quick Start Guide</a>
				19	<ol>
				20	<li><a href="#bool">Boolean Arguments</a></li>
				21	<li><a href="#alias">Argument Aliases</a></li>
				22	<li><a href="#onealternative">Selecting an alternative from a
				23	set of possibilities</a></li>
				24	<li><a href="#namedalternatives">Named alternatives</a></li>
				25	<li><a href="#list">Parsing a list of options</a></li>
				26	<li><a href="#bits">Collecting options as a set of flags</a></li>
				27	<li><a href="#description">Adding freeform text to help output</a></li>
				28	</ol></li>
				29
				30	<li><a href="#referenceguide">Reference Guide</a>
				31	<ol>
				32	<li><a href="#positional">Positional Arguments</a>
				33	<ul>
				34	<li><a href="#--">Specifying positional options with hyphens</a></li>
				35	<li><a href="#getPosition">Determining absolute position with
				36	getPosition</a></li>
				37	<li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
				38	modifier</a></li>
				39	</ul></li>
				40
				41	<li><a href="#storage">Internal vs External Storage</a></li>
				42
				43	<li><a href="#attributes">Option Attributes</a></li>
				44
				45	<li><a href="#modifiers">Option Modifiers</a>
				46	<ul>
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	47	<li><a href="#hiding">Hiding an option from <tt>--help</tt>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	48	output</a></li>
				49	<li><a href="#numoccurrences">Controlling the number of occurrences
				50	required and allowed</a></li>
				51	<li><a href="#valrequired">Controlling whether or not a value must be
				52	specified</a></li>
				53	<li><a href="#formatting">Controlling other formatting options</a></li>
				54	<li><a href="#misc">Miscellaneous option modifiers</a></li>
				55	</ul></li>
				56
				57	<li><a href="#toplevel">Top-Level Classes and Functions</a>
				58	<ul>
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	59	<li><a href="#cl::ParseCommandLineOptions">The
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	60	<tt>cl::ParseCommandLineOptions</tt> function</a></li>
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	61	<li><a href="#cl::ParseEnvironmentOptions">The
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	62	<tt>cl::ParseEnvironmentOptions</tt> function</a></li>
Chris Lattner	7b14b98	2007-12-19 19:48:49 +0000	[diff] [blame]	63	<li><a href="#cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	64	function</a></li>
				65	<li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li>
				66	<li><a href="#cl::list">The <tt>cl::list</tt> class</a></li>
				67	<li><a href="#cl::bits">The <tt>cl::bits</tt> class</a></li>
				68	<li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li>
				69	<li><a href="#cl::extrahelp">The <tt>cl::extrahelp</tt> class</a></li>
				70	</ul></li>
				71
				72	<li><a href="#builtinparsers">Builtin parsers</a>
				73	<ul>
				74	<li><a href="#genericparser">The Generic <tt>parser<t></tt>
				75	parser</a></li>
				76	<li><a href="#boolparser">The <tt>parser<bool></tt>
				77	specialization</a></li>
				78	<li><a href="#boolOrDefaultparser">The <tt>parser<boolOrDefault></tt>
				79	specialization</a></li>
				80	<li><a href="#stringparser">The <tt>parser<string></tt>
				81	specialization</a></li>
				82	<li><a href="#intparser">The <tt>parser<int></tt>
				83	specialization</a></li>
				84	<li><a href="#doubleparser">The <tt>parser<double></tt> and
				85	<tt>parser<float></tt> specializations</a></li>
				86	</ul></li>
				87	</ol></li>
				88	<li><a href="#extensionguide">Extension Guide</a>
				89	<ol>
				90	<li><a href="#customparser">Writing a custom parser</a></li>
				91	<li><a href="#explotingexternal">Exploiting external storage</a></li>
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	92	<li><a href="#dynamicopts">Dynamically adding command line
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	93	options</a></li>
				94	</ol></li>
				95	</ol>
				96
				97	<div class="doc_author">
				98	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
				99	</div>
				100
				101	<!-- *********************************************************************** -->
				102	<div class="doc_section">
				103	<a name="introduction">Introduction</a>
				104	</div>
				105	<!-- *********************************************************************** -->
				106
				107	<div class="doc_text">
				108
				109	<p>This document describes the CommandLine argument processing library. It will
				110	show you how to use it, and what it can do. The CommandLine library uses a
				111	declarative approach to specifying the command line options that your program
				112	takes. By default, these options declarations implicitly hold the value parsed
				113	for the option declared (of course this <a href="#storage">can be
				114	changed</a>).</p>
				115
				116	<p>Although there are a <b>lot</b> of command line argument parsing libraries
				117	out there in many different languages, none of them fit well with what I needed.
				118	By looking at the features and problems of other libraries, I designed the
				119	CommandLine library to have the following features:</p>
				120
				121	<ol>
				122	<li>Speed: The CommandLine library is very quick and uses little resources. The
				123	parsing time of the library is directly proportional to the number of arguments
				124	parsed, not the the number of options recognized. Additionally, command line
				125	argument values are captured transparently into user defined global variables,
				126	which can be accessed like any other variable (and with the same
				127	performance).</li>
				128
				129	<li>Type Safe: As a user of CommandLine, you don't have to worry about
				130	remembering the type of arguments that you want (is it an int? a string? a
				131	bool? an enum?) and keep casting it around. Not only does this help prevent
				132	error prone constructs, it also leads to dramatically cleaner source code.</li>
				133
				134	<li>No subclasses required: To use CommandLine, you instantiate variables that
				135	correspond to the arguments that you would like to capture, you don't subclass a
				136	parser. This means that you don't have to write <b>any</b> boilerplate
				137	code.</li>
				138
				139	<li>Globally accessible: Libraries can specify command line arguments that are
				140	automatically enabled in any tool that links to the library. This is possible
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	141	because the application doesn't have to keep a list of arguments to pass to
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	142	the parser. This also makes supporting <a href="#dynamicopts">dynamically
				143	loaded options</a> trivial.</li>
				144
				145	<li>Cleaner: CommandLine supports enum and other types directly, meaning that
				146	there is less error and more security built into the library. You don't have to
				147	worry about whether your integral command line argument accidentally got
				148	assigned a value that is not valid for your enum type.</li>
				149
				150	<li>Powerful: The CommandLine library supports many different types of
				151	arguments, from simple <a href="#boolparser">boolean flags</a> to <a
				152	href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
				153	href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
				154	href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
				155	arguments</a>. This is possible because CommandLine is...</li>
				156
				157	<li>Extensible: It is very simple to add a new argument type to CommandLine.
				158	Simply specify the parser that you want to use with the command line option when
				159	you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li>
				160
				161	<li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
				162	that you, the user, have to do. For example, it automatically provides a
				163	<tt>--help</tt> option that shows the available command line options for your
				164	tool. Additionally, it does most of the basic correctness checking for
				165	you.</li>
				166
				167	<li>Capable: The CommandLine library can handle lots of different forms of
				168	options often found in real programs. For example, <a
				169	href="#positional">positional</a> arguments, <tt>ls</tt> style <a
				170	href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
				171	-lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
				172	options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
				173	href="#cl::ConsumeAfter">interpreter style options</a>.</li>
				174
				175	</ol>
				176
				177	<p>This document will hopefully let you jump in and start using CommandLine in
				178	your utility quickly and painlessly. Additionally it should be a simple
				179	reference manual to figure out how stuff works. If it is failing in some area
				180	(or you want an extension to the library), nag the author, <a
				181	href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
				182
				183	</div>
				184
				185	<!-- *********************************************************************** -->
				186	<div class="doc_section">
				187	<a name="quickstart">Quick Start Guide</a>
				188	</div>
				189	<!-- *********************************************************************** -->
				190
				191	<div class="doc_text">
				192
				193	<p>This section of the manual runs through a simple CommandLine'ification of a
				194	basic compiler tool. This is intended to show you how to jump into using the
				195	CommandLine library in your own program, and show you some of the cool things it
				196	can do.</p>
				197
				198	<p>To start out, you need to include the CommandLine header file into your
				199	program:</p>
				200
				201	<div class="doc_code"><pre>
				202	#include "llvm/Support/CommandLine.h"
				203	</pre></div>
				204
				205	<p>Additionally, you need to add this as the first line of your main
				206	program:</p>
				207
				208	<div class="doc_code"><pre>
				209	int main(int argc, char **argv) {
				210	<a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
				211	...
				212	}
				213	</pre></div>
				214
				215	<p>... which actually parses the arguments and fills in the variable
				216	declarations.</p>
				217
				218	<p>Now that you are ready to support command line arguments, we need to tell the
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	219	system which ones we want, and what type of arguments they are. The CommandLine
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	220	library uses a declarative syntax to model command line arguments with the
				221	global variable declarations that capture the parsed values. This means that
				222	for every command line option that you would like to support, there should be a
				223	global variable declaration to capture the result. For example, in a compiler,
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	224	we would like to support the Unix-standard '<tt>-o <filename></tt>' option
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	225	to specify where to put the output. With the CommandLine library, this is
				226	represented like this:</p>
				227
				228	<a name="value_desc_example"></a>
				229	<div class="doc_code"><pre>
				230	<a href="#cl::opt">cl::opt</a><string> OutputFilename("<i>o</i>", <a href="#cl::desc">cl::desc</a>("<i>Specify output filename</i>"), <a href="#cl::value_desc">cl::value_desc</a>("<i>filename</i>"));
				231	</pre></div>
				232
				233	<p>This declares a global variable "<tt>OutputFilename</tt>" that is used to
				234	capture the result of the "<tt>o</tt>" argument (first parameter). We specify
				235	that this is a simple scalar option by using the "<tt><a
				236	href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a
				237	href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library
				238	that the data type that we are parsing is a string.</p>
				239
				240	<p>The second and third parameters (which are optional) are used to specify what
				241	to output for the "<tt>--help</tt>" option. In this case, we get a line that
				242	looks like this:</p>
				243
				244	<div class="doc_code"><pre>
				245	USAGE: compiler [options]
				246
				247	OPTIONS:
				248	-help - display available options (--help-hidden for more)
				249	<b>-o <filename> - Specify output filename</b>
				250	</pre></div>
				251
				252	<p>Because we specified that the command line option should parse using the
				253	<tt>string</tt> data type, the variable declared is automatically usable as a
				254	real string in all contexts that a normal C++ string object may be used. For
				255	example:</p>
				256
				257	<div class="doc_code"><pre>
				258	...
Chris Lattner	b917bc9	2008-03-30 16:59:21 +0000	[diff] [blame]	259	std::ofstream Output(OutputFilename.c_str());
				260	if (Output.good()) ...
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	261	...
				262	</pre></div>
				263
				264	<p>There are many different options that you can use to customize the command
				265	line option handling library, but the above example shows the general interface
				266	to these options. The options can be specified in any order, and are specified
				267	with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
				268	there are no positional dependencies to remember. The available options are
				269	discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p>
				270
				271	<p>Continuing the example, we would like to have our compiler take an input
				272	filename as well as an output filename, but we do not want the input filename to
				273	be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
				274	style of argument, the CommandLine library allows for <a
				275	href="#positional">positional</a> arguments to be specified for the program.
				276	These positional arguments are filled with command line parameters that are not
				277	in option form. We use this feature like this:</p>
				278
				279	<div class="doc_code"><pre>
				280	<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>"));
				281	</pre></div>
				282
				283	<p>This declaration indicates that the first positional argument should be
				284	treated as the input filename. Here we use the <tt><a
				285	href="#cl::init">cl::init</a></tt> option to specify an initial value for the
				286	command line option, which is used if the option is not specified (if you do not
				287	specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
				288	the default constructor for the data type is used to initialize the value).
				289	Command line options default to being optional, so if we would like to require
				290	that the user always specify an input filename, we would add the <tt><a
				291	href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
				292	<tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p>
				293
				294	<div class="doc_code"><pre>
				295	<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <b><a href="#cl::Required">cl::Required</a></b>);
				296	</pre></div>
				297
				298	<p>Again, the CommandLine library does not require the options to be specified
				299	in any particular order, so the above declaration is equivalent to:</p>
				300
				301	<div class="doc_code"><pre>
				302	<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::Required">cl::Required</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"));
				303	</pre></div>
				304
				305	<p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag,
				306	the CommandLine library will automatically issue an error if the argument is not
				307	specified, which shifts all of the command line option verification code out of
				308	your application into the library. This is just one example of how using flags
				309	can alter the default behaviour of the library, on a per-option basis. By
				310	adding one of the declarations above, the <tt>--help</tt> option synopsis is now
				311	extended to:</p>
				312
				313	<div class="doc_code"><pre>
				314	USAGE: compiler [options] <b><input file></b>
				315
				316	OPTIONS:
				317	-help - display available options (--help-hidden for more)
				318	-o <filename> - Specify output filename
				319	</pre></div>
				320
				321	<p>... indicating that an input filename is expected.</p>
				322
				323	</div>
				324
				325	<!-- ======================================================================= -->
				326	<div class="doc_subsection">
				327	<a name="bool">Boolean Arguments</a>
				328	</div>
				329
				330	<div class="doc_text">
				331
				332	<p>In addition to input and output filenames, we would like the compiler example
				333	to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
				334	file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
				335	compatibility with some of our users. We can support these by declaring options
				336	of boolean type like this:</p>
				337
				338	<div class="doc_code"><pre>
				339	<a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
				340	<a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"));
				341	<a href="#cl::opt">cl::opt</a><bool> Quiet2("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"), <a href="#cl::Hidden">cl::Hidden</a>);
				342	</pre></div>
				343
				344	<p>This does what you would expect: it declares three boolean variables
				345	("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
				346	options. Note that the "<tt>-q</tt>" option is specified with the "<a
				347	href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
				348	from being shown by the standard "<tt>--help</tt>" output (note that it is still
				349	shown in the "<tt>--help-hidden</tt>" output).</p>
				350
				351	<p>The CommandLine library uses a <a href="#builtinparsers">different parser</a>
				352	for different data types. For example, in the string case, the argument passed
				353	to the option is copied literally into the content of the string variable... we
				354	obviously cannot do that in the boolean case, however, so we must use a smarter
				355	parser. In the case of the boolean parser, it allows no options (in which case
				356	it assigns the value of true to the variable), or it allows the values
				357	"<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
				358	following inputs:</p>
				359
				360	<div class="doc_code"><pre>
				361	compiler -f # No value, 'Force' == true
				362	compiler -f=true # Value specified, 'Force' == true
				363	compiler -f=TRUE # Value specified, 'Force' == true
				364	compiler -f=FALSE # Value specified, 'Force' == false
				365	</pre></div>
				366
				367	<p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns
				368	the string values into boolean values, and rejects things like '<tt>compiler
				369	-f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
				370	href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
				371	like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
				372	library calls to parse the string value into the specified data type.</p>
				373
				374	<p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
				375
				376	<div class="doc_code"><pre>
				377	USAGE: compiler [options] <input file>
				378
				379	OPTIONS:
				380	<b>-f - Overwrite output files</b>
				381	-o - Override output filename
				382	<b>-quiet - Don't print informational messages</b>
				383	-help - display available options (--help-hidden for more)
				384	</pre></div>
				385
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	386	<p>and "<tt>compiler --help-hidden</tt>" prints this:</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	387
				388	<div class="doc_code"><pre>
				389	USAGE: compiler [options] <input file>
				390
				391	OPTIONS:
				392	-f - Overwrite output files
				393	-o - Override output filename
				394	<b>-q - Don't print informational messages</b>
				395	-quiet - Don't print informational messages
				396	-help - display available options (--help-hidden for more)
				397	</pre></div>
				398
				399	<p>This brief example has shown you how to use the '<tt><a
				400	href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
				401	arguments. In addition to simple scalar arguments, the CommandLine library also
				402	provides primitives to support CommandLine option <a href="#alias">aliases</a>,
				403	and <a href="#list">lists</a> of options.</p>
				404
				405	</div>
				406
				407	<!-- ======================================================================= -->
				408	<div class="doc_subsection">
				409	<a name="alias">Argument Aliases</a>
				410	</div>
				411
				412	<div class="doc_text">
				413
				414	<p>So far, the example works well, except for the fact that we need to check the
				415	quiet condition like this now:</p>
				416
				417	<div class="doc_code"><pre>
				418	...
				419	if (!Quiet && !Quiet2) printInformationalMessage(...);
				420	...
				421	</pre></div>
				422
				423	<p>... which is a real pain! Instead of defining two values for the same
				424	condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
				425	option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
				426	a value itself:</p>
				427
				428	<div class="doc_code"><pre>
				429	<a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
				430	<a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"));
				431	<a href="#cl::alias">cl::alias</a> QuietA("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Alias for -quiet</i>"), <a href="#cl::aliasopt">cl::aliasopt</a>(Quiet));
				432	</pre></div>
				433
				434	<p>The third line (which is the only one we modified from above) defines a
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	435	"<tt>-q</tt>" alias that updates the "<tt>Quiet</tt>" variable (as specified by
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	436	the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
				437	specified. Because aliases do not hold state, the only thing the program has to
				438	query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
				439	that they automatically hide themselves from the <tt>-help</tt> output
				440	(although, again, they are still visible in the <tt>--help-hidden
				441	output</tt>).</p>
				442
				443	<p>Now the application code can simply use:</p>
				444
				445	<div class="doc_code"><pre>
				446	...
				447	if (!Quiet) printInformationalMessage(...);
				448	...
				449	</pre></div>
				450
				451	<p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>"
				452	can be used to specify an alternative name for any variable type, and has many
				453	uses.</p>
				454
				455	</div>
				456
				457	<!-- ======================================================================= -->
				458	<div class="doc_subsection">
				459	<a name="onealternative">Selecting an alternative from a set of
				460	possibilities</a>
				461	</div>
				462
				463	<div class="doc_text">
				464
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	465	<p>So far we have seen how the CommandLine library handles builtin types like
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	466	<tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
				467	things it doesn't know about, like enums or '<tt>int*</tt>'s?</p>
				468
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	469	<p>The answer is that it uses a table-driven generic parser (unless you specify
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	470	your own parser, as described in the <a href="#extensionguide">Extension
				471	Guide</a>). This parser maps literal strings to whatever type is required, and
				472	requires you to tell it what this mapping should be.</p>
				473
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	474	<p>Let's say that we would like to add four optimization levels to our
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	475	optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>",
				476	"<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean
				477	options like above, but there are several problems with this strategy:</p>
				478
				479	<ol>
				480	<li>A user could specify more than one of the options at a time, for example,
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	481	"<tt>compiler -O3 -O2</tt>". The CommandLine library would not be able to
				482	catch this erroneous input for us.</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	483
				484	<li>We would have to test 4 different variables to see which ones are set.</li>
				485
				486	<li>This doesn't map to the numeric levels that we want... so we cannot easily
				487	see if some level >= "<tt>-O1</tt>" is enabled.</li>
				488
				489	</ol>
				490
				491	<p>To cope with these problems, we can use an enum value, and have the
				492	CommandLine library fill it in with the appropriate level directly, which is
				493	used like this:</p>
				494
				495	<div class="doc_code"><pre>
				496	enum OptLevel {
				497	g, O1, O2, O3
				498	};
				499
				500	<a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
				501	<a href="#cl::values">cl::values</a>(
				502	clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
				503	clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
				504	clEnumVal(O2, "<i>Enable default optimizations</i>"),
				505	clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
				506	clEnumValEnd));
				507
				508	...
				509	if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
				510	...
				511	</pre></div>
				512
				513	<p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
				514	"<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
				515	that are listed in the declaration (Note that the declaration list must be
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	516	terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	517	library enforces
				518	that the user can only specify one of the options, and it ensure that only valid
				519	enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
				520	command line arguments matched the enum values. With this option added, our
				521	help output now is:</p>
				522
				523	<div class="doc_code"><pre>
				524	USAGE: compiler [options] <input file>
				525
				526	OPTIONS:
				527	<b>Choose optimization level:
				528	-g - No optimizations, enable debugging
				529	-O1 - Enable trivial optimizations
				530	-O2 - Enable default optimizations
				531	-O3 - Enable expensive optimizations</b>
				532	-f - Overwrite output files
				533	-help - display available options (--help-hidden for more)
				534	-o <filename> - Specify output filename
				535	-quiet - Don't print informational messages
				536	</pre></div>
				537
				538	<p>In this case, it is sort of awkward that flag names correspond directly to
				539	enum names, because we probably don't want a enum definition named "<tt>g</tt>"
				540	in our program. Because of this, we can alternatively write this example like
				541	this:</p>
				542
				543	<div class="doc_code"><pre>
				544	enum OptLevel {
				545	Debug, O1, O2, O3
				546	};
				547
				548	<a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
				549	<a href="#cl::values">cl::values</a>(
				550	clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
				551	clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
				552	clEnumVal(O2 , "<i>Enable default optimizations</i>"),
				553	clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
				554	clEnumValEnd));
				555
				556	...
				557	if (OptimizationLevel == Debug) outputDebugInfo(...);
				558	...
				559	</pre></div>
				560
				561	<p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we
				562	can directly specify the name that the flag should get. In general a direct
				563	mapping is nice, but sometimes you can't or don't want to preserve the mapping,
				564	which is when you would use it.</p>
				565
				566	</div>
				567
				568	<!-- ======================================================================= -->
				569	<div class="doc_subsection">
				570	<a name="namedalternatives">Named Alternatives</a>
				571	</div>
				572
				573	<div class="doc_text">
				574
				575	<p>Another useful argument form is a named alternative style. We shall use this
				576	style in our compiler to specify different debug levels that can be used.
				577	Instead of each debug level being its own switch, we want to support the
				578	following options, of which only one can be specified at a time:
				579	"<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
				580	"<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
				581	our optimization level flags, but we also specify an option name. For this
				582	case, the code looks like this:</p>
				583
				584	<div class="doc_code"><pre>
				585	enum DebugLev {
				586	nodebuginfo, quick, detailed
				587	};
				588
				589	// Enable Debug Options to be specified on the command line
				590	<a href="#cl::opt">cl::opt</a><DebugLev> DebugLevel("<i>debug_level</i>", <a href="#cl::desc">cl::desc</a>("<i>Set the debugging level:</i>"),
				591	<a href="#cl::values">cl::values</a>(
				592	clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
				593	clEnumVal(quick, "<i>enable quick debug information</i>"),
				594	clEnumVal(detailed, "<i>enable detailed debug information</i>"),
				595	clEnumValEnd));
				596	</pre></div>
				597
				598	<p>This definition defines an enumerated command line variable of type "<tt>enum
				599	DebugLev</tt>", which works exactly the same way as before. The difference here
				600	is just the interface exposed to the user of your program and the help output by
				601	the "<tt>--help</tt>" option:</p>
				602
				603	<div class="doc_code"><pre>
				604	USAGE: compiler [options] <input file>
				605
				606	OPTIONS:
				607	Choose optimization level:
				608	-g - No optimizations, enable debugging
				609	-O1 - Enable trivial optimizations
				610	-O2 - Enable default optimizations
				611	-O3 - Enable expensive optimizations
				612	<b>-debug_level - Set the debugging level:
				613	=none - disable debug information
				614	=quick - enable quick debug information
				615	=detailed - enable detailed debug information</b>
				616	-f - Overwrite output files
				617	-help - display available options (--help-hidden for more)
				618	-o <filename> - Specify output filename
				619	-quiet - Don't print informational messages
				620	</pre></div>
				621
				622	<p>Again, the only structural difference between the debug level declaration and
				623	the optimization level declaration is that the debug level declaration includes
				624	an option name (<tt>"debug_level"</tt>), which automatically changes how the
				625	library processes the argument. The CommandLine library supports both forms so
				626	that you can choose the form most appropriate for your application.</p>
				627
				628	</div>
				629
				630	<!-- ======================================================================= -->
				631	<div class="doc_subsection">
				632	<a name="list">Parsing a list of options</a>
				633	</div>
				634
				635	<div class="doc_text">
				636
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	637	<p>Now that we have the standard run-of-the-mill argument types out of the way,
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	638	lets get a little wild and crazy. Lets say that we want our optimizer to accept
				639	a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
				640	might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
				641	this case, the order of the arguments and the number of appearances is very
				642	important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
				643	template is for. First, start by defining an enum of the optimizations that you
				644	would like to perform:</p>
				645
				646	<div class="doc_code"><pre>
				647	enum Opts {
				648	// 'inline' is a C++ keyword, so name it 'inlining'
				649	dce, constprop, inlining, strip
				650	};
				651	</pre></div>
				652
				653	<p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
				654
				655	<div class="doc_code"><pre>
				656	<a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
				657	<a href="#cl::values">cl::values</a>(
				658	clEnumVal(dce , "<i>Dead Code Elimination</i>"),
				659	clEnumVal(constprop , "<i>Constant Propagation</i>"),
				660	clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
				661	clEnumVal(strip , "<i>Strip Symbols</i>"),
				662	clEnumValEnd));
				663	</pre></div>
				664
				665	<p>This defines a variable that is conceptually of the type
				666	"<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
				667	vector methods:</p>
				668
				669	<div class="doc_code"><pre>
				670	for (unsigned i = 0; i != OptimizationList.size(); ++i)
				671	switch (OptimizationList[i])
				672	...
				673	</pre></div>
				674
				675	<p>... to iterate through the list of options specified.</p>
				676
				677	<p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is
				678	completely general and may be used with any data types or other arguments that
				679	you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One
				680	especially useful way to use a list is to capture all of the positional
				681	arguments together if there may be more than one specified. In the case of a
				682	linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to
				683	capture them into a list. This is naturally specified as:</p>
				684
				685	<div class="doc_code"><pre>
				686	...
				687	<a href="#cl::list">cl::list</a><std::string> InputFilenames(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<Input files>"), <a href="#cl::OneOrMore">cl::OneOrMore</a>);
				688	...
				689	</pre></div>
				690
				691	<p>This variable works just like a "<tt>vector<string></tt>" object. As
				692	such, accessing the list is simple, just like above. In this example, we used
				693	the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
				694	CommandLine library that it is an error if the user does not specify any
				695	<tt>.o</tt> files on our command line. Again, this just reduces the amount of
				696	checking we have to do.</p>
				697
				698	</div>
				699
				700	<!-- ======================================================================= -->
				701	<div class="doc_subsection">
				702	<a name="bits">Collecting options as a set of flags</a>
				703	</div>
				704
				705	<div class="doc_text">
				706
				707	<p>Instead of collecting sets of options in a list, it is also possible to
				708	gather information for enum values in a <b>bit vector</b>. The represention used by
				709	the <a href="#bits"><tt>cl::bits</tt></a> class is an <tt>unsigned</tt>
				710	integer. An enum value is represented by a 0/1 in the enum's ordinal value bit
				711	position. 1 indicating that the enum was specified, 0 otherwise. As each
				712	specified value is parsed, the resulting enum's bit is set in the option's bit
				713	vector:</p>
				714
				715	<div class="doc_code"><pre>
				716	<i>bits</i> \|= 1 << (unsigned)<i>enum</i>;
				717	</pre></div>
				718
				719	<p>Options that are specified multiple times are redundant. Any instances after
				720	the first are discarded.</p>
				721
				722	<p>Reworking the above list example, we could replace <a href="#list">
				723	<tt>cl::list</tt></a> with <a href="#bits"><tt>cl::bits</tt></a>:</p>
				724
				725	<div class="doc_code"><pre>
				726	<a href="#cl::bits">cl::bits</a><Opts> OptimizationBits(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
				727	<a href="#cl::values">cl::values</a>(
				728	clEnumVal(dce , "<i>Dead Code Elimination</i>"),
				729	clEnumVal(constprop , "<i>Constant Propagation</i>"),
				730	clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
				731	clEnumVal(strip , "<i>Strip Symbols</i>"),
				732	clEnumValEnd));
				733	</pre></div>
				734
				735	<p>To test to see if <tt>constprop</tt> was specified, we can use the
				736	<tt>cl:bits::isSet</tt> function:</p>
				737
				738	<div class="doc_code"><pre>
				739	if (OptimizationBits.isSet(constprop)) {
				740	...
				741	}
				742	</pre></div>
				743
				744	<p>It's also possible to get the raw bit vector using the
				745	<tt>cl::bits::getBits</tt> function:</p>
				746
				747	<div class="doc_code"><pre>
				748	unsigned bits = OptimizationBits.getBits();
				749	</pre></div>
				750
				751	<p>Finally, if external storage is used, then the location specified must be of
				752	<b>type</b> <tt>unsigned</tt>. In all other ways a <a
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	753	href="#bits"><tt>cl::bits</tt></a> option is equivalent to a <a
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	754	href="#list"> <tt>cl::list</tt></a> option.</p>
				755
				756	</div>
				757
				758
				759	<!-- ======================================================================= -->
				760	<div class="doc_subsection">
				761	<a name="description">Adding freeform text to help output</a>
				762	</div>
				763
				764	<div class="doc_text">
				765
				766	<p>As our program grows and becomes more mature, we may decide to put summary
				767	information about what it does into the help output. The help output is styled
				768	to look similar to a Unix <tt>man</tt> page, providing concise information about
				769	a program. Unix <tt>man</tt> pages, however often have a description about what
				770	the program does. To add this to your CommandLine program, simply pass a third
				771	argument to the <a
				772	href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
				773	call in main. This additional argument is then printed as the overview
				774	information for your program, allowing you to include any additional information
				775	that you want. For example:</p>
				776
				777	<div class="doc_code"><pre>
				778	int main(int argc, char **argv) {
				779	<a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
				780	" This program blah blah blah...\n");
				781	...
				782	}
				783	</pre></div>
				784
				785	<p>would yield the help output:</p>
				786
				787	<div class="doc_code"><pre>
				788	<b>OVERVIEW: CommandLine compiler example
				789
				790	This program blah blah blah...</b>
				791
				792	USAGE: compiler [options] <input file>
				793
				794	OPTIONS:
				795	...
				796	-help - display available options (--help-hidden for more)
				797	-o <filename> - Specify output filename
				798	</pre></div>
				799
				800	</div>
				801
				802
				803	<!-- *********************************************************************** -->
				804	<div class="doc_section">
				805	<a name="referenceguide">Reference Guide</a>
				806	</div>
				807	<!-- *********************************************************************** -->
				808
				809	<div class="doc_text">
				810
				811	<p>Now that you know the basics of how to use the CommandLine library, this
				812	section will give you the detailed information you need to tune how command line
				813	options work, as well as information on more "advanced" command line option
				814	processing capabilities.</p>
				815
				816	</div>
				817
				818	<!-- ======================================================================= -->
				819	<div class="doc_subsection">
				820	<a name="positional">Positional Arguments</a>
				821	</div>
				822
				823	<div class="doc_text">
				824
				825	<p>Positional arguments are those arguments that are not named, and are not
				826	specified with a hyphen. Positional arguments should be used when an option is
				827	specified by its position alone. For example, the standard Unix <tt>grep</tt>
				828	tool takes a regular expression argument, and an optional filename to search
				829	through (which defaults to standard input if a filename is not specified).
				830	Using the CommandLine library, this would be specified as:</p>
				831
				832	<div class="doc_code"><pre>
				833	<a href="#cl::opt">cl::opt</a><string> Regex (<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><regular expression></i>"), <a href="#cl::Required">cl::Required</a>);
				834	<a href="#cl::opt">cl::opt</a><string> Filename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>"));
				835	</pre></div>
				836
				837	<p>Given these two option declarations, the <tt>--help</tt> output for our grep
				838	replacement would look like this:</p>
				839
				840	<div class="doc_code"><pre>
				841	USAGE: spiffygrep [options] <b><regular expression> <input file></b>
				842
				843	OPTIONS:
				844	-help - display available options (--help-hidden for more)
				845	</pre></div>
				846
				847	<p>... and the resultant program could be used just like the standard
				848	<tt>grep</tt> tool.</p>
				849
				850	<p>Positional arguments are sorted by their order of construction. This means
				851	that command line options will be ordered according to how they are listed in a
				852	.cpp file, but will not have an ordering defined if the positional arguments
				853	are defined in multiple .cpp files. The fix for this problem is simply to
				854	define all of your positional arguments in one .cpp file.</p>
				855
				856	</div>
				857
				858
				859	<!-- _______________________________________________________________________ -->
				860	<div class="doc_subsubsection">
				861	<a name="--">Specifying positional options with hyphens</a>
				862	</div>
				863
				864	<div class="doc_text">
				865
				866	<p>Sometimes you may want to specify a value to your positional argument that
				867	starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
				868	first, you will have trouble doing this, because it will try to find an argument
				869	named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
				870	Note that the system <tt>grep</tt> has the same problem:</p>
				871
				872	<div class="doc_code"><pre>
				873	$ spiffygrep '-foo' test.txt
				874	Unknown command line argument '-foo'. Try: spiffygrep --help'
				875
				876	$ grep '-foo' test.txt
				877	grep: illegal option -- f
				878	grep: illegal option -- o
				879	grep: illegal option -- o
				880	Usage: grep -hblcnsviw pattern file . . .
				881	</pre></div>
				882
				883	<p>The solution for this problem is the same for both your tool and the system
				884	version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
				885	the command line, it is telling the program that all options after the
				886	'<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
				887	can use it like this:</p>
				888
				889	<div class="doc_code"><pre>
				890	$ spiffygrep -- -foo test.txt
				891	...output...
				892	</pre></div>
				893
				894	</div>
				895
				896	<!-- _______________________________________________________________________ -->
				897	<div class="doc_subsubsection">
				898	<a name="getPosition">Determining absolute position with getPosition()</a>
				899	</div>
				900	<div class="doc_text">
				901	<p>Sometimes an option can affect or modify the meaning of another option. For
				902	example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells
				903	<tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force
				904	the file to be interpreted as if it contained source code in language
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	905	<tt>LANG</tt>. In order to handle this properly , you need to know the
				906	absolute position of each argument, especially those in lists, so their
				907	interaction(s) can be applied correctly. This is also useful for options like
				908	<tt>-llibname</tt> which is actually a positional argument that starts with
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	909	a dash.</p>
				910	<p>So, generally, the problem is that you have two <tt>cl::list</tt> variables
				911	that interact in some way. To ensure the correct interaction, you can use the
				912	<tt>cl::list::getPosition(optnum)</tt> method. This method returns the
				913	absolute position (as found on the command line) of the <tt>optnum</tt>
				914	item in the <tt>cl::list</tt>.</p>
				915	<p>The idiom for usage is like this:</p>
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	916
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	917	<div class="doc_code"><pre>
				918	static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	919	static cl::list<std::string> Libraries("l", cl::ZeroOrMore);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	920
				921	int main(int argc, char**argv) {
				922	// ...
				923	std::vector<std::string>::iterator fileIt = Files.begin();
				924	std::vector<std::string>::iterator libIt = Libraries.begin();
				925	unsigned libPos = 0, filePos = 0;
				926	while ( 1 ) {
				927	if ( libIt != Libraries.end() )
				928	libPos = Libraries.getPosition( libIt - Libraries.begin() );
				929	else
				930	libPos = 0;
				931	if ( fileIt != Files.end() )
				932	filePos = Files.getPosition( fileIt - Files.begin() );
				933	else
				934	filePos = 0;
				935
				936	if ( filePos != 0 && (libPos == 0 \|\| filePos < libPos) ) {
				937	// Source File Is next
				938	++fileIt;
				939	}
				940	else if ( libPos != 0 && (filePos == 0 \|\| libPos < filePos) ) {
				941	// Library is next
				942	++libIt;
				943	}
				944	else
				945	break; // we're done with the list
				946	}
				947	}</pre></div>
				948
				949	<p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an
				950	<tt>unsigned getPosition()</tt> option that will provide the absolute position
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	951	of that option. You can apply the same approach as above with a
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	952	<tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p>
				953	</div>
				954
				955	<!-- _______________________________________________________________________ -->
				956	<div class="doc_subsubsection">
				957	<a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
				958	</div>
				959
				960	<div class="doc_text">
				961
				962	<p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
				963	used to construct programs that use "interpreter style" option processing. With
				964	this style of option processing, all arguments specified after the last
				965	positional argument are treated as special interpreter arguments that are not
				966	interpreted by the command line argument.</p>
				967
				968	<p>As a concrete example, lets say we are developing a replacement for the
				969	standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
				970	you specify options to the shell itself (like <tt>-x</tt> which turns on trace
				971	output), then you specify the name of the script to run, then you specify
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	972	arguments to the script. These arguments to the script are parsed by the Bourne
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	973	shell command line option processor, but are not interpreted as options to the
				974	shell itself. Using the CommandLine library, we would specify this as:</p>
				975
				976	<div class="doc_code"><pre>
				977	<a href="#cl::opt">cl::opt</a><string> Script(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input script></i>"), <a href="#cl::init">cl::init</a>("-"));
				978	<a href="#cl::list">cl::list</a><string> Argv(<a href="#cl::ConsumeAfter">cl::ConsumeAfter</a>, <a href="#cl::desc">cl::desc</a>("<i><program arguments>...</i>"));
				979	<a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
				980	</pre></div>
				981
				982	<p>which automatically provides the help output:</p>
				983
				984	<div class="doc_code"><pre>
				985	USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
				986
				987	OPTIONS:
				988	-help - display available options (--help-hidden for more)
				989	<b>-x - Enable trace output</b>
				990	</pre></div>
				991
				992	<p>At runtime, if we run our new shell replacement as `<tt>spiffysh -x test.sh
				993	-a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
				994	<tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
				995	<tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
				996	were specified after the last positional argument (which is the script
				997	name).</p>
				998
				999	<p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
				1000	be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
				1001	per program, there must be at least one <a href="#positional">positional
				1002	argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
				1003	positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
				1004	href="#cl::list">cl::list</a> option.</p>
				1005
				1006	</div>
				1007
				1008	<!-- ======================================================================= -->
				1009	<div class="doc_subsection">
				1010	<a name="storage">Internal vs External Storage</a>
				1011	</div>
				1012
				1013	<div class="doc_text">
				1014
				1015	<p>By default, all command line options automatically hold the value that they
				1016	parse from the command line. This is very convenient in the common case,
				1017	especially when combined with the ability to define command line options in the
				1018	files that use them. This is called the internal storage model.</p>
				1019
				1020	<p>Sometimes, however, it is nice to separate the command line option processing
				1021	code from the storage of the value parsed. For example, lets say that we have a
				1022	'<tt>-debug</tt>' option that we would like to use to enable debug information
				1023	across the entire body of our program. In this case, the boolean value
				1024	controlling the debug code should be globally accessable (in a header file, for
				1025	example) yet the command line option processing code should not be exposed to
				1026	all of these clients (requiring lots of .cpp files to #include
				1027	<tt>CommandLine.h</tt>).</p>
				1028
				1029	<p>To do this, set up your .h file with your option, like this for example:</p>
				1030
				1031	<div class="doc_code">
				1032	<pre>
				1033	<i>// DebugFlag.h - Get access to the '-debug' command line option
				1034	//
				1035
				1036	// DebugFlag - This boolean is set to true if the '-debug' command line option
				1037	// is specified. This should probably not be referenced directly, instead, use
				1038	// the DEBUG macro below.
				1039	//</i>
				1040	extern bool DebugFlag;
				1041
				1042	<i>// DEBUG macro - This macro should be used by code to emit debug information.
				1043	// In the '-debug' option is specified on the command line, and if this is a
				1044	// debug build, then the code specified as the option to the macro will be
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1045	// executed. Otherwise it will not be.</i>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1046	<span class="doc_hilite">#ifdef NDEBUG
				1047	#define DEBUG(X)
				1048	#else
				1049	#define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0)
				1050	<span class="doc_hilite">#endif</span>
				1051	</pre>
				1052	</div>
				1053
				1054	<p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
				1055	<tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
				1056	set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1057	an additional argument to our command line argument processor, and we specify
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1058	where to fill in with the <a href="#cl::location">cl::location</a>
				1059	attribute:</p>
				1060
				1061	<div class="doc_code">
				1062	<pre>
				1063	bool DebugFlag; <i>// the actual value</i>
				1064	static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
				1065	Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>, <a href="#cl::location">cl::location</a>(DebugFlag));
				1066	</pre>
				1067	</div>
				1068
				1069	<p>In the above example, we specify "<tt>true</tt>" as the second argument to
				1070	the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the
				1071	template should not maintain a copy of the value itself. In addition to this,
				1072	we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so
				1073	that <tt>DebugFlag</tt> is automatically set.</p>
				1074
				1075	</div>
				1076
				1077	<!-- ======================================================================= -->
				1078	<div class="doc_subsection">
				1079	<a name="attributes">Option Attributes</a>
				1080	</div>
				1081
				1082	<div class="doc_text">
				1083
				1084	<p>This section describes the basic attributes that you can specify on
				1085	options.</p>
				1086
				1087	<ul>
				1088
				1089	<li>The option name attribute (which is required for all options, except <a
				1090	href="#positional">positional options</a>) specifies what the option name is.
				1091	This option is specified in simple double quotes:
				1092
				1093	<pre>
				1094	<a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
				1095	</pre>
				1096
				1097	</li>
				1098
				1099	<li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
				1100	description for the option to be shown in the <tt>--help</tt> output for the
				1101	program.</li>
				1102
				1103	<li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
				1104	specifies a string that can be used to fine tune the <tt>--help</tt> output for
				1105	a command line option. Look <a href="#value_desc_example">here</a> for an
				1106	example.</li>
				1107
				1108	<li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
				1109	inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
				1110	not specified then the command line option value defaults to the value created
				1111	by the default constructor for the type. <b>Warning</b>: If you specify both
				1112	<b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
				1113	you must specify <b><tt>cl::location</tt></b> first, so that when the
				1114	command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
				1115	initial value. (You will get an error at runtime if you don't put them in
				1116	the right order.)</li>
				1117
				1118	<li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
				1119	store the value for a parsed command line option if using external storage. See
				1120	the section on <a href="#storage">Internal vs External Storage</a> for more
				1121	information.</li>
				1122
				1123	<li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
				1124	specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is
				1125	an alias for.</li>
				1126
				1127	<li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
				1128	the string-to-value mapping to be used by the generic parser. It takes a
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	1129	<b>clEnumValEnd terminated</b> list of (option, value, description) triplets
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1130	that
				1131	specify the option name, the value mapped to, and the description shown in the
				1132	<tt>--help</tt> for the tool. Because the generic parser is used most
				1133	frequently with enum values, two macros are often useful:
				1134
				1135	<ol>
				1136
				1137	<li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
				1138	nice simple way to specify a triplet for an enum. This macro automatically
				1139	makes the option name be the same as the enum name. The first option to the
				1140	macro is the enum, the second is the description for the command line
				1141	option.</li>
				1142
				1143	<li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
				1144	specify macro options where the option name doesn't equal the enum name. For
				1145	this macro, the first argument is the enum value, the second is the flag name,
				1146	and the second is the description.</li>
				1147
				1148	</ol>
				1149
				1150	You will get a compile time error if you try to use cl::values with a parser
				1151	that does not support it.</li>
				1152
				1153	</ul>
				1154
				1155	</div>
				1156
				1157	<!-- ======================================================================= -->
				1158	<div class="doc_subsection">
				1159	<a name="modifiers">Option Modifiers</a>
				1160	</div>
				1161
				1162	<div class="doc_text">
				1163
				1164	<p>Option modifiers are the flags and expressions that you pass into the
				1165	constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
				1166	href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
				1167	tweak how options are parsed and how <tt>--help</tt> output is generated to fit
				1168	your application well.</p>
				1169
				1170	<p>These options fall into five main catagories:</p>
				1171
				1172	<ol>
				1173	<li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
				1174	<li><a href="#numoccurrences">Controlling the number of occurrences
				1175	required and allowed</a></li>
				1176	<li><a href="#valrequired">Controlling whether or not a value must be
				1177	specified</a></li>
				1178	<li><a href="#formatting">Controlling other formatting options</a></li>
				1179	<li><a href="#misc">Miscellaneous option modifiers</a></li>
				1180	</ol>
				1181
				1182	<p>It is not possible to specify two options from the same catagory (you'll get
				1183	a runtime error) to a single option, except for options in the miscellaneous
				1184	catagory. The CommandLine library specifies defaults for all of these settings
				1185	that are the most useful in practice and the most common, which mean that you
				1186	usually shouldn't have to worry about these.</p>
				1187
				1188	</div>
				1189
				1190	<!-- _______________________________________________________________________ -->
				1191	<div class="doc_subsubsection">
				1192	<a name="hiding">Hiding an option from <tt>--help</tt> output</a>
				1193	</div>
				1194
				1195	<div class="doc_text">
				1196
				1197	<p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
				1198	<tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
				1199	appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
				1200	compiled program:</p>
				1201
				1202	<ul>
				1203
				1204	<li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
				1205	(which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1206	href="#cl::list">cl::list</a></tt> options) indicates the option is to appear
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1207	in both help listings.</li>
				1208
				1209	<li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1210	default for <tt><a href="#cl::alias">cl::alias</a></tt> options) indicates that
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1211	the option should not appear in the <tt>--help</tt> output, but should appear in
				1212	the <tt>--help-hidden</tt> output.</li>
				1213
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1214	<li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1215	indicates that the option should not appear in any help output.</li>
				1216
				1217	</ul>
				1218
				1219	</div>
				1220
				1221	<!-- _______________________________________________________________________ -->
				1222	<div class="doc_subsubsection">
				1223	<a name="numoccurrences">Controlling the number of occurrences required and
				1224	allowed</a>
				1225	</div>
				1226
				1227	<div class="doc_text">
				1228
				1229	<p>This group of options is used to control how many time an option is allowed
				1230	(or required) to be specified on the command line of your program. Specifying a
				1231	value for this setting allows the CommandLine library to do error checking for
				1232	you.</p>
				1233
				1234	<p>The allowed values for this option group are:</p>
				1235
				1236	<ul>
				1237
				1238	<li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
				1239	is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
				1240	href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
				1241	allow either zero or one occurrence of the option to be specified.</li>
				1242
				1243	<li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
				1244	(which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
				1245	indicates that your program will allow the option to be specified zero or more
				1246	times.</li>
				1247
				1248	<li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
				1249	indicates that the specified option must be specified exactly one time.</li>
				1250
				1251	<li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
				1252	indicates that the option must be specified at least one time.</li>
				1253
				1254	<li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1255	href="#positional">Positional arguments section</a>.</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1256
				1257	</ul>
				1258
				1259	<p>If an option is not specified, then the value of the option is equal to the
				1260	value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
				1261	the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
				1262	option value is initialized with the default constructor for the data type.</p>
				1263
				1264	<p>If an option is specified multiple times for an option of the <tt><a
				1265	href="#cl::opt">cl::opt</a></tt> class, only the last value will be
				1266	retained.</p>
				1267
				1268	</div>
				1269
				1270	<!-- _______________________________________________________________________ -->
				1271	<div class="doc_subsubsection">
				1272	<a name="valrequired">Controlling whether or not a value must be specified</a>
				1273	</div>
				1274
				1275	<div class="doc_text">
				1276
				1277	<p>This group of options is used to control whether or not the option allows a
				1278	value to be present. In the case of the CommandLine library, a value is either
				1279	specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
				1280	string (e.g. '<tt>-o a.out</tt>').</p>
				1281
				1282	<p>The allowed values for this option group are:</p>
				1283
				1284	<ul>
				1285
				1286	<li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
				1287	(which is the default for <tt>bool</tt> typed options) specifies that it is
				1288	acceptable to have a value, or not. A boolean argument can be enabled just by
				1289	appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
				1290	If an option is specified with this mode, it is illegal for the value to be
				1291	provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
				1292	get this behavior, you must use the <a
				1293	href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
				1294
				1295	<li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
				1296	(which is the default for all other types except for <a
				1297	href="#onealternative">unnamed alternatives using the generic parser</a>)
				1298	specifies that a value must be provided. This mode informs the command line
				1299	library that if an option is not provides with an equal sign, that the next
				1300	argument provided must be the value. This allows things like '<tt>-o
				1301	a.out</tt>' to work.</li>
				1302
				1303	<li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
				1304	modifier (which is the default for <a href="#onealternative">unnamed
				1305	alternatives using the generic parser</a>) indicates that it is a runtime error
				1306	for the user to specify a value. This can be provided to disallow users from
				1307	providing options to boolean options (like '<tt>-foo=true</tt>').</li>
				1308
				1309	</ul>
				1310
				1311	<p>In general, the default values for this option group work just like you would
				1312	want them to. As mentioned above, you can specify the <a
				1313	href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
				1314	argument to restrict your command line parser. These options are mostly useful
				1315	when <a href="#extensionguide">extending the library</a>.</p>
				1316
				1317	</div>
				1318
				1319	<!-- _______________________________________________________________________ -->
				1320	<div class="doc_subsubsection">
				1321	<a name="formatting">Controlling other formatting options</a>
				1322	</div>
				1323
				1324	<div class="doc_text">
				1325
				1326	<p>The formatting option group is used to specify that the command line option
				1327	has special abilities and is otherwise different from other command line
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1328	arguments. As usual, you can only specify one of these arguments at most.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1329
				1330	<ul>
				1331
				1332	<li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
				1333	modifier (which is the default all options) specifies that this option is
				1334	"normal".</li>
				1335
				1336	<li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1337	specifies that this is a positional argument that does not have a command line
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1338	option associated with it. See the <a href="#positional">Positional
				1339	Arguments</a> section for more information.</li>
				1340
				1341	<li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
				1342	specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
				1343
				1344	<li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
				1345	that this option prefixes its value. With 'Prefix' options, the equal sign does
				1346	not separate the value from the option name specified. Instead, the value is
				1347	everything after the prefix, including any equal sign if present. This is useful
				1348	for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a
				1349	linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the
				1350	'<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list)
				1351	options, that have the <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b>
				1352	modifier added to allow the CommandLine library to recognize them. Note that
				1353	<b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> options must not have the
				1354	<b><tt><a href="#cl::ValueDisallowed">cl::ValueDisallowed</a></tt></b> modifier
				1355	specified.</li>
				1356
				1357	<li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1358	to implement Unix-style tools (like <tt>ls</tt>) that have lots of single letter
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1359	arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
				1360	command actually enables four different options, all of which are single
				1361	letters. Note that <b><tt><a href="#cl::Grouping">cl::Grouping</a></tt></b>
				1362	options cannot have values.</li>
				1363
				1364	</ul>
				1365
				1366	<p>The CommandLine library does not restrict how you use the <b><tt><a
				1367	href="#cl::Prefix">cl::Prefix</a></tt></b> or <b><tt><a
				1368	href="#cl::Grouping">cl::Grouping</a></tt></b> modifiers, but it is possible to
				1369	specify ambiguous argument settings. Thus, it is possible to have multiple
				1370	letter options that are prefix or grouping options, and they will still work as
				1371	designed.</p>
				1372
				1373	<p>To do this, the CommandLine library uses a greedy algorithm to parse the
				1374	input option into (potentially multiple) prefix and grouping options. The
				1375	strategy basically looks like this:</p>
				1376
				1377	<div class="doc_code"><tt>parse(string OrigInput) {</tt>
				1378
				1379	<ol>
				1380	<li><tt>string input = OrigInput;</tt>
				1381	<li><tt>if (isOption(input)) return getOption(input).parse();</tt>    <i>// Normal option</i>
				1382	<li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt>    <i>// Remove the last letter</i>
				1383	<li><tt>if (input.empty()) return error();</tt>    <i>// No matching option</i>
				1384	<li><tt>if (getOption(input).isPrefix())<br>
				1385	return getOption(input).parse(input);</tt>
				1386	<li><tt>while (!input.empty()) {    <i>// Must be grouping options</i><br>
				1387	getOption(input).parse();<br>
				1388	OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
				1389	input = OrigInput;<br>
				1390	while (!isOption(input) && !input.empty()) input.pop_back();<br>
				1391	}</tt>
				1392	<li><tt>if (!OrigInput.empty()) error();</tt></li>
				1393	</ol>
				1394
				1395	<p><tt>}</tt></p>
				1396	</div>
				1397
				1398	</div>
				1399
				1400	<!-- _______________________________________________________________________ -->
				1401	<div class="doc_subsubsection">
				1402	<a name="misc">Miscellaneous option modifiers</a>
				1403	</div>
				1404
				1405	<div class="doc_text">
				1406
				1407	<p>The miscellaneous option modifiers are the only flags where you can specify
				1408	more than one flag from the set: they are not mutually exclusive. These flags
				1409	specify boolean properties that modify the option.</p>
				1410
				1411	<ul>
				1412
				1413	<li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
				1414	indicates that any commas specified for an option's value should be used to
				1415	split the value up into multiple values for the option. For example, these two
				1416	options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
				1417	"<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
				1418	makes sense to be used in a case where the option is allowed to accept one or
				1419	more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
				1420
				1421	<li><a name="cl::PositionalEatsArgs">The
				1422	<b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
				1423	positional arguments, and only makes sense for lists) indicates that positional
				1424	argument should consume any strings after it (including strings that start with
				1425	a "-") up until another recognized positional argument. For example, if you
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1426	have two "eating" positional arguments, "<tt>pos1</tt>" and "<tt>pos2</tt>", the
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1427	string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
				1428	-baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
				1429	"<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
				1430
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	1431	<li><a name="cl::Sink">The <b><tt>cl::Sink</tt></b></a> modifier is
				1432	used to handle unknown options. If there is at least one option with
				1433	<b><tt>cl::Sink</tt></b></a> modifier specified, the parser passes
				1434	unrecognized option strings to it as values instead of signaling an
				1435	error. As with <b><tt>cl::CommaSeparated</tt></b></a>, this modifier
				1436	only makes sense with a <a href="#cl::list">cl::list</a> option.</li>
				1437
				1438
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1439	</ul>
				1440
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	1441	<p>So far, these are the only three miscellaneous option modifiers.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1442
				1443	</div>
				1444
				1445	<!-- ======================================================================= -->
				1446	<div class="doc_subsection">
				1447	<a name="toplevel">Top-Level Classes and Functions</a>
				1448	</div>
				1449
				1450	<div class="doc_text">
				1451
				1452	<p>Despite all of the built-in flexibility, the CommandLine option library
				1453	really only consists of one function (<a
				1454	href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
				1455	and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
				1456	href="#cl::list"><tt>cl::list</tt></a>, and <a
				1457	href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
				1458	classes in detail.</p>
				1459
				1460	</div>
				1461
				1462	<!-- _______________________________________________________________________ -->
				1463	<div class="doc_subsubsection">
				1464	<a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
				1465	function</a>
				1466	</div>
				1467
				1468	<div class="doc_text">
				1469
				1470	<p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
				1471	directly from <tt>main</tt>, and is used to fill in the values of all of the
				1472	command line option variables once <tt>argc</tt> and <tt>argv</tt> are
				1473	available.</p>
				1474
				1475	<p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
				1476	(<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
				1477	which holds <a href="#description">additional extra text</a> to emit when the
				1478	<tt>--help</tt> option is invoked.</p>
				1479
				1480	</div>
				1481
				1482	<!-- _______________________________________________________________________ -->
				1483	<div class="doc_subsubsection">
				1484	<a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
				1485	function</a>
				1486	</div>
				1487
				1488	<div class="doc_text">
				1489
				1490	<p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
				1491	as <a
				1492	href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
				1493	except that it is designed to take values for options from an environment
				1494	variable, for those cases in which reading the command line is not convenient or
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1495	desired. It fills in the values of all the command line option variables just
				1496	like <a
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1497	href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
				1498	does.</p>
				1499
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1500	<p>It takes three parameters: the name of the program (since <tt>argv</tt> may
				1501	not be available, it can't just look in <tt>argv[0]</tt>), the name of the
				1502	environment variable to examine, and the optional
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1503	<a href="#description">additional extra text</a> to emit when the
				1504	<tt>--help</tt> option is invoked.</p>
				1505
				1506	<p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
				1507	variable's value up into words and then process them using
				1508	<a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
				1509	<b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
				1510	quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
				1511	be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
				1512	which is different from what you would get from the shell with the same
				1513	input.</p>
				1514
				1515	</div>
				1516
				1517	<!-- _______________________________________________________________________ -->
				1518	<div class="doc_subsubsection">
				1519	<a name="cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt>
				1520	function</a>
				1521	</div>
				1522
				1523	<div class="doc_text">
				1524
				1525	<p>The <tt>cl::SetVersionPrinter</tt> function is designed to be called
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1526	directly from <tt>main</tt> and <i>before</i>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1527	<tt>cl::ParseCommandLineOptions</tt>. Its use is optional. It simply arranges
				1528	for a function to be called in response to the <tt>--version</tt> option instead
				1529	of having the <tt>CommandLine</tt> library print out the usual version string
				1530	for LLVM. This is useful for programs that are not part of LLVM but wish to use
				1531	the <tt>CommandLine</tt> facilities. Such programs should just define a small
				1532	function that takes no arguments and returns <tt>void</tt> and that prints out
				1533	whatever version information is appropriate for the program. Pass the address
				1534	of that function to <tt>cl::SetVersionPrinter</tt> to arrange for it to be
				1535	called when the <tt>--version</tt> option is given by the user.</p>
				1536
				1537	</div>
				1538	<!-- _______________________________________________________________________ -->
				1539	<div class="doc_subsubsection">
				1540	<a name="cl::opt">The <tt>cl::opt</tt> class</a>
				1541	</div>
				1542
				1543	<div class="doc_text">
				1544
				1545	<p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
				1546	options, and is the one used most of the time. It is a templated class which
				1547	can take up to three arguments (all except for the first have default values
				1548	though):</p>
				1549
				1550	<div class="doc_code"><pre>
				1551	<b>namespace</b> cl {
				1552	<b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
				1553	<b>class</b> ParserClass = parser<DataType> >
				1554	<b>class</b> opt;
				1555	}
				1556	</pre></div>
				1557
				1558	<p>The first template argument specifies what underlying data type the command
				1559	line argument is, and is used to select a default parser implementation. The
				1560	second template argument is used to specify whether the option should contain
				1561	the storage for the option (the default) or whether external storage should be
				1562	used to contain the value parsed for the option (see <a href="#storage">Internal
				1563	vs External Storage</a> for more information).</p>
				1564
				1565	<p>The third template argument specifies which parser to use. The default value
				1566	selects an instantiation of the <tt>parser</tt> class based on the underlying
				1567	data type of the option. In general, this default works well for most
				1568	applications, so this option is only used when using a <a
				1569	href="#customparser">custom parser</a>.</p>
				1570
				1571	</div>
				1572
				1573	<!-- _______________________________________________________________________ -->
				1574	<div class="doc_subsubsection">
				1575	<a name="cl::list">The <tt>cl::list</tt> class</a>
				1576	</div>
				1577
				1578	<div class="doc_text">
				1579
				1580	<p>The <tt>cl::list</tt> class is the class used to represent a list of command
				1581	line options. It too is a templated class which can take up to three
				1582	arguments:</p>
				1583
				1584	<div class="doc_code"><pre>
				1585	<b>namespace</b> cl {
				1586	<b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
				1587	<b>class</b> ParserClass = parser<DataType> >
				1588	<b>class</b> list;
				1589	}
				1590	</pre></div>
				1591
				1592	<p>This class works the exact same as the <a
				1593	href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
				1594	the <b>type</b> of the external storage, not a boolean value. For this class,
				1595	the marker type '<tt>bool</tt>' is used to indicate that internal storage should
				1596	be used.</p>
				1597
				1598	</div>
				1599
				1600	<!-- _______________________________________________________________________ -->
				1601	<div class="doc_subsubsection">
				1602	<a name="cl::bits">The <tt>cl::bits</tt> class</a>
				1603	</div>
				1604
				1605	<div class="doc_text">
				1606
				1607	<p>The <tt>cl::bits</tt> class is the class used to represent a list of command
				1608	line options in the form of a bit vector. It is also a templated class which
				1609	can take up to three arguments:</p>
				1610
				1611	<div class="doc_code"><pre>
				1612	<b>namespace</b> cl {
				1613	<b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
				1614	<b>class</b> ParserClass = parser<DataType> >
				1615	<b>class</b> bits;
				1616	}
				1617	</pre></div>
				1618
				1619	<p>This class works the exact same as the <a
				1620	href="#cl::opt"><tt>cl::lists</tt></a> class, except that the second argument
				1621	must be of <b>type</b> <tt>unsigned</tt> if external storage is used.</p>
				1622
				1623	</div>
				1624
				1625	<!-- _______________________________________________________________________ -->
				1626	<div class="doc_subsubsection">
				1627	<a name="cl::alias">The <tt>cl::alias</tt> class</a>
				1628	</div>
				1629
				1630	<div class="doc_text">
				1631
				1632	<p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
				1633	aliases for other arguments.</p>
				1634
				1635	<div class="doc_code"><pre>
				1636	<b>namespace</b> cl {
				1637	<b>class</b> alias;
				1638	}
				1639	</pre></div>
				1640
				1641	<p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
				1642	used to specify which option this is an alias for. Alias arguments default to
				1643	being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
				1644	the conversion from string to data.</p>
				1645
				1646	</div>
				1647
				1648	<!-- _______________________________________________________________________ -->
				1649	<div class="doc_subsubsection">
				1650	<a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a>
				1651	</div>
				1652
				1653	<div class="doc_text">
				1654
				1655	<p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra
				1656	help text to be printed out for the <tt>--help</tt> option.</p>
				1657
				1658	<div class="doc_code"><pre>
				1659	<b>namespace</b> cl {
				1660	<b>struct</b> extrahelp;
				1661	}
				1662	</pre></div>
				1663
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	1664	<p>To use the extrahelp, simply construct one with a <tt>const char*</tt>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1665	parameter to the constructor. The text passed to the constructor will be printed
				1666	at the bottom of the help message, verbatim. Note that multiple
				1667	<tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If
				1668	your tool needs to print additional help information, put all that help into a
				1669	single <tt>cl::extrahelp</tt> instance.</p>
				1670	<p>For example:</p>
				1671	<div class="doc_code"><pre>
				1672	cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
				1673	</pre></div>
				1674	</div>
				1675
				1676	<!-- ======================================================================= -->
				1677	<div class="doc_subsection">
				1678	<a name="builtinparsers">Builtin parsers</a>
				1679	</div>
				1680
				1681	<div class="doc_text">
				1682
				1683	<p>Parsers control how the string value taken from the command line is
				1684	translated into a typed value, suitable for use in a C++ program. By default,
				1685	the CommandLine library uses an instance of <tt>parser<type></tt> if the
				1686	command line option specifies that it uses values of type '<tt>type</tt>'.
				1687	Because of this, custom option processing is specified with specializations of
				1688	the '<tt>parser</tt>' class.</p>
				1689
				1690	<p>The CommandLine library provides the following builtin parser
				1691	specializations, which are sufficient for most applications. It can, however,
				1692	also be extended to work with new data types and new ways of interpreting the
				1693	same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
				1694	details on this type of library extension.</p>
				1695
				1696	<ul>
				1697
				1698	<li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
				1699	can be used to map strings values to any data type, through the use of the <a
				1700	href="#cl::values">cl::values</a> property, which specifies the mapping
				1701	information. The most common use of this parser is for parsing enum values,
				1702	which allows you to use the CommandLine library for all of the error checking to
				1703	make sure that only valid enum values are specified (as opposed to accepting
				1704	arbitrary strings). Despite this, however, the generic parser class can be used
				1705	for any data type.</li>
				1706
				1707	<li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
				1708	is used to convert boolean strings to a boolean value. Currently accepted
				1709	strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
				1710	"<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
				1711
				1712	<li><a name="boolOrDefaultparser">The <b><tt>parser<boolOrDefault></tt>
				1713	specialization</b></a> is used for cases where the value is boolean,
				1714	but we also need to know whether the option was specified at all. boolOrDefault
				1715	is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. This parser accepts
				1716	the same strings as <b><tt>parser<bool></tt></b>.</li>
				1717
				1718	<li><a name="stringparser">The <b><tt>parser<string></tt>
				1719	specialization</b></a> simply stores the parsed string into the string value
				1720	specified. No conversion or modification of the data is performed.</li>
				1721
				1722	<li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
				1723	uses the C <tt>strtol</tt> function to parse the string input. As such, it will
				1724	accept a decimal number (with an optional '+' or '-' prefix) which must start
				1725	with a non-zero digit. It accepts octal numbers, which are identified with a
				1726	'<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
				1727	'<tt>0x</tt>' or '<tt>0X</tt>'.</li>
				1728
				1729	<li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
				1730	<b><tt>parser<float></tt> specializations</b> use the standard C
				1731	<tt>strtod</tt> function to convert floating point strings into floating point
				1732	values. As such, a broad range of string formats is supported, including
				1733	exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
				1734	</li>
				1735
				1736	</ul>
				1737
				1738	</div>
				1739
				1740	<!-- *********************************************************************** -->
				1741	<div class="doc_section">
				1742	<a name="extensionguide">Extension Guide</a>
				1743	</div>
				1744	<!-- *********************************************************************** -->
				1745
				1746	<div class="doc_text">
				1747
				1748	<p>Although the CommandLine library has a lot of functionality built into it
				1749	already (as discussed previously), one of its true strengths lie in its
				1750	extensibility. This section discusses how the CommandLine library works under
				1751	the covers and illustrates how to do some simple, common, extensions.</p>
				1752
				1753	</div>
				1754
				1755	<!-- ======================================================================= -->
				1756	<div class="doc_subsection">
				1757	<a name="customparser">Writing a custom parser</a>
				1758	</div>
				1759
				1760	<div class="doc_text">
				1761
				1762	<p>One of the simplest and most common extensions is the use of a custom parser.
				1763	As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
				1764	of the CommandLine library that turns string input from the user into a
				1765	particular parsed data type, validating the input in the process.</p>
				1766
				1767	<p>There are two ways to use a new parser:</p>
				1768
				1769	<ol>
				1770
				1771	<li>
				1772
				1773	<p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
				1774	your custom data type.<p>
				1775
				1776	<p>This approach has the advantage that users of your custom data type will
				1777	automatically use your custom parser whenever they define an option with a value
				1778	type of your data type. The disadvantage of this approach is that it doesn't
				1779	work if your fundamental data type is something that is already supported.</p>
				1780
				1781	</li>
				1782
				1783	<li>
				1784
				1785	<p>Write an independent class, using it explicitly from options that need
				1786	it.</p>
				1787
				1788	<p>This approach works well in situations where you would line to parse an
				1789	option using special syntax for a not-very-special data-type. The drawback of
				1790	this approach is that users of your parser have to be aware that they are using
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1791	your parser instead of the builtin ones.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1792
				1793	</li>
				1794
				1795	</ol>
				1796
				1797	<p>To guide the discussion, we will discuss a custom parser that accepts file
				1798	sizes, specified with an optional unit after the numeric size. For example, we
				1799	would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
				1800	this case, the underlying data type we want to parse into is
				1801	'<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
				1802	this the default for all <tt>unsigned</tt> options.</p>
				1803
				1804	<p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
				1805
				1806	<div class="doc_code"><pre>
				1807	<b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
				1808	<i>// parse - Return true on error.</i>
				1809	<b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
				1810	<b>unsigned</b> &Val);
				1811	};
				1812	</pre></div>
				1813
				1814	<p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1815	fill in the default, boiler plate code for us. We give it the data type that
				1816	we parse into, the last argument to the <tt>parse</tt> method, so that clients of
				1817	our custom parser know what object type to pass in to the parse method. (Here we
				1818	declare that we parse into '<tt>unsigned</tt>' variables.)</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1819
				1820	<p>For most purposes, the only method that must be implemented in a custom
				1821	parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
				1822	whenever the option is invoked, passing in the option itself, the option name,
				1823	the string to parse, and a reference to a return value. If the string to parse
Chris Lattner	00e02f6	2008-01-09 19:28:50 +0000	[diff] [blame]	1824	is not well-formed, the parser should output an error message and return true.
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1825	Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
				1826	our example, we implement <tt>parse</tt> as:</p>
				1827
				1828	<div class="doc_code"><pre>
				1829	<b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
				1830	<b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
				1831	<b>const char</b> *ArgStart = Arg.c_str();
				1832	<b>char</b> *End;
Anton Korobeynikov	1c1e900	2008-02-20 12:38:31 +0000	[diff] [blame]	1833
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1834	<i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
				1835	Val = (unsigned)strtol(ArgStart, &End, 0);
				1836
				1837	<b>while</b> (1) {
				1838	<b>switch</b> (*End++) {
				1839	<b>case</b> 0: <b>return</b> false; <i>// No error</i>
				1840	<b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
				1841	<b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
				1842	<b>break</b>;
				1843
				1844	<b>case</b> 'g': <b>case</b> 'G': Val = 10241024*1024; <b>break</b>;
				1845	<b>case</b> 'm': <b>case</b> 'M': Val = 10241024; <b>break</b>;
				1846	<b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
				1847
				1848	default:
				1849	<i>// Print an error message if unrecognized character!</i>
				1850	<b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
				1851	}
				1852	}
				1853	}
				1854	</pre></div>
				1855
				1856	<p>This function implements a very simple parser for the kinds of strings we are
				1857	interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
				1858	example), it is good enough for this example. Note that we use the option
				1859	itself to print out the error message (the <tt>error</tt> method always returns
				1860	true) in order to get a nice error message (shown below). Now that we have our
				1861	parser class, we can use it like this:</p>
				1862
				1863	<div class="doc_code"><pre>
				1864	<b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
				1865	MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
				1866	<a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
				1867	</pre></div>
				1868
				1869	<p>Which adds this to the output of our program:</p>
				1870
				1871	<div class="doc_code"><pre>
				1872	OPTIONS:
				1873	-help - display available options (--help-hidden for more)
				1874	...
				1875	<b>-max-file-size=<size> - Maximum file size to accept</b>
				1876	</pre></div>
				1877
				1878	<p>And we can test that our parse works correctly now (the test program just
				1879	prints out the max-file-size argument value):</p>
				1880
				1881	<div class="doc_code"><pre>
				1882	$ ./test
				1883	MFS: 0
				1884	$ ./test -max-file-size=123MB
				1885	MFS: 128974848
				1886	$ ./test -max-file-size=3G
				1887	MFS: 3221225472
				1888	$ ./test -max-file-size=dog
				1889	-max-file-size option: 'dog' value invalid for file size argument!
				1890	</pre></div>
				1891
				1892	<p>It looks like it works. The error message that we get is nice and helpful,
				1893	and we seem to accept reasonable file sizes. This wraps up the "custom parser"
				1894	tutorial.</p>
				1895
				1896	</div>
				1897
				1898	<!-- ======================================================================= -->
				1899	<div class="doc_subsection">
				1900	<a name="explotingexternal">Exploiting external storage</a>
				1901	</div>
				1902
				1903	<div class="doc_text">
				1904	<p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that
				1905	will automatically be included in any program that links with that library.
				1906	This is a feature. However, sometimes it is necessary to know the value of the
				1907	command line option outside of the library. In these cases the library does or
				1908	should provide an external storage location that is accessible to users of the
				1909	library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the
				1910	<tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt>
				1911	flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p>
				1912
				1913	<p>TODO: complete this section</p>
				1914
				1915	</div>
				1916
				1917	<!-- ======================================================================= -->
				1918	<div class="doc_subsection">
				1919	<a name="dynamicopts">Dynamically adding command line options</a>
				1920	</div>
				1921
				1922	<div class="doc_text">
				1923
				1924	<p>TODO: fill in this section</p>
				1925
				1926	</div>
				1927
				1928	<!-- *********************************************************************** -->
				1929
				1930	<hr>
				1931	<address>
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				1936
				1937	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				1938	<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
				1939	Last modified: $Date$
				1940	</address>
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