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| <div class="doc_title"> |
| CommandLine 2.0 Library Manual |
| </div> |
| |
| <ol> |
| <li><a href="#introduction">Introduction</a></li> |
| |
| <li><a href="#quickstart">Quick Start Guide</a> |
| <ol> |
| <li><a href="#bool">Boolean Arguments</a></li> |
| <li><a href="#alias">Argument Aliases</a></li> |
| <li><a href="#onealternative">Selecting an alternative from a |
| set of possibilities</a></li> |
| <li><a href="#namedalternatives">Named alternatives</a></li> |
| <li><a href="#list">Parsing a list of options</a></li> |
| <li><a href="#description">Adding freeform text to help output</a></li> |
| </ol></li> |
| |
| <li><a href="#referenceguide">Reference Guide</a> |
| <ol> |
| <li><a href="#positional">Positional Arguments</a> |
| <ul> |
| <li><a href="#--">Specifying positional options with hyphens</a></li> |
| <li><a href="#getPosition">Determining absolute position with |
| getPosition</a></li> |
| <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> |
| modifier</a></li> |
| </ul></li> |
| |
| <li><a href="#storage">Internal vs External Storage</a></li> |
| |
| <li><a href="#attributes">Option Attributes</a></li> |
| |
| <li><a href="#modifiers">Option Modifiers</a> |
| <ul> |
| <li><a href="#hiding">Hiding an option from <tt>--help</tt> |
| output</a></li> |
| <li><a href="#numoccurrences">Controlling the number of occurrences |
| required and allowed</a></li> |
| <li><a href="#valrequired">Controlling whether or not a value must be |
| specified</a></li> |
| <li><a href="#formatting">Controlling other formatting options</a></li> |
| <li><a href="#misc">Miscellaneous option modifiers</a></li> |
| </ul></li> |
| |
| <li><a href="#toplevel">Top-Level Classes and Functions</a> |
| <ul> |
| <li><a href="#cl::ParseCommandLineOptions">The |
| <tt>cl::ParseCommandLineOptions</tt> function</a></li> |
| <li><a href="#cl::ParseEnvironmentOptions">The |
| <tt>cl::ParseEnvironmentOptions</tt> function</a></li> |
| <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li> |
| <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li> |
| <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li> |
| <li><a href="#cl::extrahelp">The <tt>cl::extrahelp</tt> class</a></li> |
| </ul></li> |
| |
| <li><a href="#builtinparsers">Builtin parsers</a> |
| <ul> |
| <li><a href="#genericparser">The Generic <tt>parser<t></tt> |
| parser</a></li> |
| <li><a href="#boolparser">The <tt>parser<bool></tt> |
| specialization</a></li> |
| <li><a href="#stringparser">The <tt>parser<string></tt> |
| specialization</a></li> |
| <li><a href="#intparser">The <tt>parser<int></tt> |
| specialization</a></li> |
| <li><a href="#doubleparser">The <tt>parser<double></tt> and |
| <tt>parser<float></tt> specializations</a></li> |
| </ul></li> |
| </ol></li> |
| <li><a href="#extensionguide">Extension Guide</a> |
| <ol> |
| <li><a href="#customparser">Writing a custom parser</a></li> |
| <li><a href="#explotingexternal">Exploiting external storage</a></li> |
| <li><a href="#dynamicopts">Dynamically adding command line |
| options</a></li> |
| </ol></li> |
| </ol> |
| |
| <div class="doc_author"> |
| <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p> |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="introduction">Introduction</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>This document describes the CommandLine argument processing library. It will |
| show you how to use it, and what it can do. The CommandLine library uses a |
| declarative approach to specifying the command line options that your program |
| takes. By default, these options declarations implicitly hold the value parsed |
| for the option declared (of course this <a href="#storage">can be |
| changed</a>).</p> |
| |
| <p>Although there are a <b>lot</b> of command line argument parsing libraries |
| out there in many different languages, none of them fit well with what I needed. |
| By looking at the features and problems of other libraries, I designed the |
| CommandLine library to have the following features:</p> |
| |
| <ol> |
| <li>Speed: The CommandLine library is very quick and uses little resources. The |
| parsing time of the library is directly proportional to the number of arguments |
| parsed, not the the number of options recognized. Additionally, command line |
| argument values are captured transparently into user defined global variables, |
| which can be accessed like any other variable (and with the same |
| performance).</li> |
| |
| <li>Type Safe: As a user of CommandLine, you don't have to worry about |
| remembering the type of arguments that you want (is it an int? a string? a |
| bool? an enum?) and keep casting it around. Not only does this help prevent |
| error prone constructs, it also leads to dramatically cleaner source code.</li> |
| |
| <li>No subclasses required: To use CommandLine, you instantiate variables that |
| correspond to the arguments that you would like to capture, you don't subclass a |
| parser. This means that you don't have to write <b>any</b> boilerplate |
| code.</li> |
| |
| <li>Globally accessible: Libraries can specify command line arguments that are |
| automatically enabled in any tool that links to the library. This is possible |
| because the application doesn't have to keep a "list" of arguments to pass to |
| the parser. This also makes supporting <a href="#dynamicopts">dynamically |
| loaded options</a> trivial.</li> |
| |
| <li>Cleaner: CommandLine supports enum and other types directly, meaning that |
| there is less error and more security built into the library. You don't have to |
| worry about whether your integral command line argument accidentally got |
| assigned a value that is not valid for your enum type.</li> |
| |
| <li>Powerful: The CommandLine library supports many different types of |
| arguments, from simple <a href="#boolparser">boolean flags</a> to <a |
| href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a |
| href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a |
| href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of |
| arguments</a>. This is possible because CommandLine is...</li> |
| |
| <li>Extensible: It is very simple to add a new argument type to CommandLine. |
| Simply specify the parser that you want to use with the command line option when |
| you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li> |
| |
| <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work |
| that you, the user, have to do. For example, it automatically provides a |
| <tt>--help</tt> option that shows the available command line options for your |
| tool. Additionally, it does most of the basic correctness checking for |
| you.</li> |
| |
| <li>Capable: The CommandLine library can handle lots of different forms of |
| options often found in real programs. For example, <a |
| href="#positional">positional</a> arguments, <tt>ls</tt> style <a |
| href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls |
| -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a> |
| options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a |
| href="#cl::ConsumeAfter">interpreter style options</a>.</li> |
| |
| </ol> |
| |
| <p>This document will hopefully let you jump in and start using CommandLine in |
| your utility quickly and painlessly. Additionally it should be a simple |
| reference manual to figure out how stuff works. If it is failing in some area |
| (or you want an extension to the library), nag the author, <a |
| href="mailto:sabre@nondot.org">Chris Lattner</a>.</p> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="quickstart">Quick Start Guide</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>This section of the manual runs through a simple CommandLine'ification of a |
| basic compiler tool. This is intended to show you how to jump into using the |
| CommandLine library in your own program, and show you some of the cool things it |
| can do.</p> |
| |
| <p>To start out, you need to include the CommandLine header file into your |
| program:</p> |
| |
| <div class="doc_code"><pre> |
| #include "Support/CommandLine.h" |
| </pre></div> |
| |
| <p>Additionally, you need to add this as the first line of your main |
| program:</p> |
| |
| <div class="doc_code"><pre> |
| int main(int argc, char **argv) { |
| <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv); |
| ... |
| } |
| </pre></div> |
| |
| <p>... which actually parses the arguments and fills in the variable |
| declarations.</p> |
| |
| <p>Now that you are ready to support command line arguments, we need to tell the |
| system which ones we want, and what type of argument they are. The CommandLine |
| library uses a declarative syntax to model command line arguments with the |
| global variable declarations that capture the parsed values. This means that |
| for every command line option that you would like to support, there should be a |
| global variable declaration to capture the result. For example, in a compiler, |
| we would like to support the unix standard '<tt>-o <filename></tt>' option |
| to specify where to put the output. With the CommandLine library, this is |
| represented like this:</p> |
| |
| <a name="value_desc_example"></a> |
| <div class="doc_code"><pre> |
| <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>")); |
| </pre></div> |
| |
| <p>This declares a global variable "<tt>OutputFilename</tt>" that is used to |
| capture the result of the "<tt>o</tt>" argument (first parameter). We specify |
| that this is a simple scalar option by using the "<tt><a |
| href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a |
| href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library |
| that the data type that we are parsing is a string.</p> |
| |
| <p>The second and third parameters (which are optional) are used to specify what |
| to output for the "<tt>--help</tt>" option. In this case, we get a line that |
| looks like this:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: compiler [options] |
| |
| OPTIONS: |
| -help - display available options (--help-hidden for more) |
| <b>-o <filename> - Specify output filename</b> |
| </pre></div> |
| |
| <p>Because we specified that the command line option should parse using the |
| <tt>string</tt> data type, the variable declared is automatically usable as a |
| real string in all contexts that a normal C++ string object may be used. For |
| example:</p> |
| |
| <div class="doc_code"><pre> |
| ... |
| ofstream Output(OutputFilename.c_str()); |
| if (Out.good()) ... |
| ... |
| </pre></div> |
| |
| <p>There are many different options that you can use to customize the command |
| line option handling library, but the above example shows the general interface |
| to these options. The options can be specified in any order, and are specified |
| with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so |
| there are no positional dependencies to remember. The available options are |
| discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p> |
| |
| <p>Continuing the example, we would like to have our compiler take an input |
| filename as well as an output filename, but we do not want the input filename to |
| be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this |
| style of argument, the CommandLine library allows for <a |
| href="#positional">positional</a> arguments to be specified for the program. |
| These positional arguments are filled with command line parameters that are not |
| in option form. We use this feature like this:</p> |
| |
| <div class="doc_code"><pre> |
| <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>")); |
| </pre></div> |
| |
| <p>This declaration indicates that the first positional argument should be |
| treated as the input filename. Here we use the <tt><a |
| href="#cl::init">cl::init</a></tt> option to specify an initial value for the |
| command line option, which is used if the option is not specified (if you do not |
| specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then |
| the default constructor for the data type is used to initialize the value). |
| Command line options default to being optional, so if we would like to require |
| that the user always specify an input filename, we would add the <tt><a |
| href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the |
| <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p> |
| |
| <div class="doc_code"><pre> |
| <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>); |
| </pre></div> |
| |
| <p>Again, the CommandLine library does not require the options to be specified |
| in any particular order, so the above declaration is equivalent to:</p> |
| |
| <div class="doc_code"><pre> |
| <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>")); |
| </pre></div> |
| |
| <p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag, |
| the CommandLine library will automatically issue an error if the argument is not |
| specified, which shifts all of the command line option verification code out of |
| your application into the library. This is just one example of how using flags |
| can alter the default behaviour of the library, on a per-option basis. By |
| adding one of the declarations above, the <tt>--help</tt> option synopsis is now |
| extended to:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: compiler [options] <b><input file></b> |
| |
| OPTIONS: |
| -help - display available options (--help-hidden for more) |
| -o <filename> - Specify output filename |
| </pre></div> |
| |
| <p>... indicating that an input filename is expected.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="bool">Boolean Arguments</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>In addition to input and output filenames, we would like the compiler example |
| to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output |
| file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards |
| compatibility with some of our users. We can support these by declaring options |
| of boolean type like this:</p> |
| |
| <div class="doc_code"><pre> |
| <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>")); |
| <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>")); |
| <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>); |
| </pre></div> |
| |
| <p>This does what you would expect: it declares three boolean variables |
| ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these |
| options. Note that the "<tt>-q</tt>" option is specified with the "<a |
| href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it |
| from being shown by the standard "<tt>--help</tt>" output (note that it is still |
| shown in the "<tt>--help-hidden</tt>" output).</p> |
| |
| <p>The CommandLine library uses a <a href="#builtinparsers">different parser</a> |
| for different data types. For example, in the string case, the argument passed |
| to the option is copied literally into the content of the string variable... we |
| obviously cannot do that in the boolean case, however, so we must use a smarter |
| parser. In the case of the boolean parser, it allows no options (in which case |
| it assigns the value of true to the variable), or it allows the values |
| "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the |
| following inputs:</p> |
| |
| <div class="doc_code"><pre> |
| compiler -f # No value, 'Force' == true |
| compiler -f=true # Value specified, 'Force' == true |
| compiler -f=TRUE # Value specified, 'Force' == true |
| compiler -f=FALSE # Value specified, 'Force' == false |
| </pre></div> |
| |
| <p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns |
| the string values into boolean values, and rejects things like '<tt>compiler |
| -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a |
| href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work |
| like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C |
| library calls to parse the string value into the specified data type.</p> |
| |
| <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| <b>-f - Overwrite output files</b> |
| -o - Override output filename |
| <b>-quiet - Don't print informational messages</b> |
| -help - display available options (--help-hidden for more) |
| </pre></div> |
| |
| <p>and "<tt>opt --help-hidden</tt>" prints this:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| -f - Overwrite output files |
| -o - Override output filename |
| <b>-q - Don't print informational messages</b> |
| -quiet - Don't print informational messages |
| -help - display available options (--help-hidden for more) |
| </pre></div> |
| |
| <p>This brief example has shown you how to use the '<tt><a |
| href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line |
| arguments. In addition to simple scalar arguments, the CommandLine library also |
| provides primitives to support CommandLine option <a href="#alias">aliases</a>, |
| and <a href="#list">lists</a> of options.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="alias">Argument Aliases</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>So far, the example works well, except for the fact that we need to check the |
| quiet condition like this now:</p> |
| |
| <div class="doc_code"><pre> |
| ... |
| if (!Quiet && !Quiet2) printInformationalMessage(...); |
| ... |
| </pre></div> |
| |
| <p>... which is a real pain! Instead of defining two values for the same |
| condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>" |
| option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing |
| a value itself:</p> |
| |
| <div class="doc_code"><pre> |
| <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>")); |
| <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>")); |
| <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)); |
| </pre></div> |
| |
| <p>The third line (which is the only one we modified from above) defines a |
| "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by |
| the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is |
| specified. Because aliases do not hold state, the only thing the program has to |
| query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is |
| that they automatically hide themselves from the <tt>-help</tt> output |
| (although, again, they are still visible in the <tt>--help-hidden |
| output</tt>).</p> |
| |
| <p>Now the application code can simply use:</p> |
| |
| <div class="doc_code"><pre> |
| ... |
| if (!Quiet) printInformationalMessage(...); |
| ... |
| </pre></div> |
| |
| <p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>" |
| can be used to specify an alternative name for any variable type, and has many |
| uses.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="onealternative">Selecting an alternative from a set of |
| possibilities</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>So far, we have seen how the CommandLine library handles builtin types like |
| <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle |
| things it doesn't know about, like enums or '<tt>int*</tt>'s?</p> |
| |
| <p>The answer is that it uses a table driven generic parser (unless you specify |
| your own parser, as described in the <a href="#extensionguide">Extension |
| Guide</a>). This parser maps literal strings to whatever type is required, and |
| requires you to tell it what this mapping should be.</p> |
| |
| <p>Lets say that we would like to add four optimization levels to our |
| optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>", |
| "<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean |
| options like above, but there are several problems with this strategy:</p> |
| |
| <ol> |
| <li>A user could specify more than one of the options at a time, for example, |
| "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this |
| erroneous input for us.</li> |
| |
| <li>We would have to test 4 different variables to see which ones are set.</li> |
| |
| <li>This doesn't map to the numeric levels that we want... so we cannot easily |
| see if some level >= "<tt>-O1</tt>" is enabled.</li> |
| |
| </ol> |
| |
| <p>To cope with these problems, we can use an enum value, and have the |
| CommandLine library fill it in with the appropriate level directly, which is |
| used like this:</p> |
| |
| <div class="doc_code"><pre> |
| enum OptLevel { |
| g, O1, O2, O3 |
| }; |
| |
| <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"), |
| <a href="#cl::values">cl::values</a>( |
| clEnumVal(g , "<i>No optimizations, enable debugging</i>"), |
| clEnumVal(O1, "<i>Enable trivial optimizations</i>"), |
| clEnumVal(O2, "<i>Enable default optimizations</i>"), |
| clEnumVal(O3, "<i>Enable expensive optimizations</i>"), |
| clEnumValEnd)); |
| |
| ... |
| if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); |
| ... |
| </pre></div> |
| |
| <p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the |
| "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values |
| that are listed in the declaration (Note that the declaration list must be |
| terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine |
| library enforces |
| that the user can only specify one of the options, and it ensure that only valid |
| enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the |
| command line arguments matched the enum values. With this option added, our |
| help output now is:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| <b>Choose optimization level: |
| -g - No optimizations, enable debugging |
| -O1 - Enable trivial optimizations |
| -O2 - Enable default optimizations |
| -O3 - Enable expensive optimizations</b> |
| -f - Overwrite output files |
| -help - display available options (--help-hidden for more) |
| -o <filename> - Specify output filename |
| -quiet - Don't print informational messages |
| </pre></div> |
| |
| <p>In this case, it is sort of awkward that flag names correspond directly to |
| enum names, because we probably don't want a enum definition named "<tt>g</tt>" |
| in our program. Because of this, we can alternatively write this example like |
| this:</p> |
| |
| <div class="doc_code"><pre> |
| enum OptLevel { |
| Debug, O1, O2, O3 |
| }; |
| |
| <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"), |
| <a href="#cl::values">cl::values</a>( |
| clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"), |
| clEnumVal(O1 , "<i>Enable trivial optimizations</i>"), |
| clEnumVal(O2 , "<i>Enable default optimizations</i>"), |
| clEnumVal(O3 , "<i>Enable expensive optimizations</i>"), |
| clEnumValEnd)); |
| |
| ... |
| if (OptimizationLevel == Debug) outputDebugInfo(...); |
| ... |
| </pre></div> |
| |
| <p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we |
| can directly specify the name that the flag should get. In general a direct |
| mapping is nice, but sometimes you can't or don't want to preserve the mapping, |
| which is when you would use it.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="namedalternatives">Named Alternatives</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Another useful argument form is a named alternative style. We shall use this |
| style in our compiler to specify different debug levels that can be used. |
| Instead of each debug level being its own switch, we want to support the |
| following options, of which only one can be specified at a time: |
| "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>", |
| "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as |
| our optimization level flags, but we also specify an option name. For this |
| case, the code looks like this:</p> |
| |
| <div class="doc_code"><pre> |
| enum DebugLev { |
| nodebuginfo, quick, detailed |
| }; |
| |
| // Enable Debug Options to be specified on the command line |
| <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>"), |
| <a href="#cl::values">cl::values</a>( |
| clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"), |
| clEnumVal(quick, "<i>enable quick debug information</i>"), |
| clEnumVal(detailed, "<i>enable detailed debug information</i>"), |
| clEnumValEnd)); |
| </pre></div> |
| |
| <p>This definition defines an enumerated command line variable of type "<tt>enum |
| DebugLev</tt>", which works exactly the same way as before. The difference here |
| is just the interface exposed to the user of your program and the help output by |
| the "<tt>--help</tt>" option:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| Choose optimization level: |
| -g - No optimizations, enable debugging |
| -O1 - Enable trivial optimizations |
| -O2 - Enable default optimizations |
| -O3 - Enable expensive optimizations |
| <b>-debug_level - Set the debugging level: |
| =none - disable debug information |
| =quick - enable quick debug information |
| =detailed - enable detailed debug information</b> |
| -f - Overwrite output files |
| -help - display available options (--help-hidden for more) |
| -o <filename> - Specify output filename |
| -quiet - Don't print informational messages |
| </pre></div> |
| |
| <p>Again, the only structural difference between the debug level declaration and |
| the optimization level declaration is that the debug level declaration includes |
| an option name (<tt>"debug_level"</tt>), which automatically changes how the |
| library processes the argument. The CommandLine library supports both forms so |
| that you can choose the form most appropriate for your application.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="list">Parsing a list of options</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Now that we have the standard run of the mill argument types out of the way, |
| lets get a little wild and crazy. Lets say that we want our optimizer to accept |
| a <b>list</b> of optimizations to perform, allowing duplicates. For example, we |
| might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In |
| this case, the order of the arguments and the number of appearances is very |
| important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>" |
| template is for. First, start by defining an enum of the optimizations that you |
| would like to perform:</p> |
| |
| <div class="doc_code"><pre> |
| enum Opts { |
| // 'inline' is a C++ keyword, so name it 'inlining' |
| dce, constprop, inlining, strip |
| }; |
| </pre></div> |
| |
| <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p> |
| |
| <div class="doc_code"><pre> |
| <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"), |
| <a href="#cl::values">cl::values</a>( |
| clEnumVal(dce , "<i>Dead Code Elimination</i>"), |
| clEnumVal(constprop , "<i>Constant Propagation</i>"), |
| clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"), |
| clEnumVal(strip , "<i>Strip Symbols</i>"), |
| clEnumValEnd)); |
| </pre></div> |
| |
| <p>This defines a variable that is conceptually of the type |
| "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard |
| vector methods:</p> |
| |
| <div class="doc_code"><pre> |
| for (unsigned i = 0; i != OptimizationList.size(); ++i) |
| switch (OptimizationList[i]) |
| ... |
| </pre></div> |
| |
| <p>... to iterate through the list of options specified.</p> |
| |
| <p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is |
| completely general and may be used with any data types or other arguments that |
| you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One |
| especially useful way to use a list is to capture all of the positional |
| arguments together if there may be more than one specified. In the case of a |
| linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to |
| capture them into a list. This is naturally specified as:</p> |
| |
| <div class="doc_code"><pre> |
| ... |
| <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>); |
| ... |
| </pre></div> |
| |
| <p>This variable works just like a "<tt>vector<string></tt>" object. As |
| such, accessing the list is simple, just like above. In this example, we used |
| the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the |
| CommandLine library that it is an error if the user does not specify any |
| <tt>.o</tt> files on our command line. Again, this just reduces the amount of |
| checking we have to do.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="description">Adding freeform text to help output</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>As our program grows and becomes more mature, we may decide to put summary |
| information about what it does into the help output. The help output is styled |
| to look similar to a Unix <tt>man</tt> page, providing concise information about |
| a program. Unix <tt>man</tt> pages, however often have a description about what |
| the program does. To add this to your CommandLine program, simply pass a third |
| argument to the <a |
| href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> |
| call in main. This additional argument is then printed as the overview |
| information for your program, allowing you to include any additional information |
| that you want. For example:</p> |
| |
| <div class="doc_code"><pre> |
| int main(int argc, char **argv) { |
| <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n" |
| " This program blah blah blah...\n"); |
| ... |
| } |
| </pre></div> |
| |
| <p>would yield the help output:</p> |
| |
| <div class="doc_code"><pre> |
| <b>OVERVIEW: CommandLine compiler example |
| |
| This program blah blah blah...</b> |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| ... |
| -help - display available options (--help-hidden for more) |
| -o <filename> - Specify output filename |
| </pre></div> |
| |
| </div> |
| |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="referenceguide">Reference Guide</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>Now that you know the basics of how to use the CommandLine library, this |
| section will give you the detailed information you need to tune how command line |
| options work, as well as information on more "advanced" command line option |
| processing capabilities.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="positional">Positional Arguments</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Positional arguments are those arguments that are not named, and are not |
| specified with a hyphen. Positional arguments should be used when an option is |
| specified by its position alone. For example, the standard Unix <tt>grep</tt> |
| tool takes a regular expression argument, and an optional filename to search |
| through (which defaults to standard input if a filename is not specified). |
| Using the CommandLine library, this would be specified as:</p> |
| |
| <div class="doc_code"><pre> |
| <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>); |
| <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>")); |
| </pre></div> |
| |
| <p>Given these two option declarations, the <tt>--help</tt> output for our grep |
| replacement would look like this:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: spiffygrep [options] <b><regular expression> <input file></b> |
| |
| OPTIONS: |
| -help - display available options (--help-hidden for more) |
| </pre></div> |
| |
| <p>... and the resultant program could be used just like the standard |
| <tt>grep</tt> tool.</p> |
| |
| <p>Positional arguments are sorted by their order of construction. This means |
| that command line options will be ordered according to how they are listed in a |
| .cpp file, but will not have an ordering defined if the positional arguments |
| are defined in multiple .cpp files. The fix for this problem is simply to |
| define all of your positional arguments in one .cpp file.</p> |
| |
| </div> |
| |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="--">Specifying positional options with hyphens</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Sometimes you may want to specify a value to your positional argument that |
| starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At |
| first, you will have trouble doing this, because it will try to find an argument |
| named '<tt>-foo</tt>', and will fail (and single quotes will not save you). |
| Note that the system <tt>grep</tt> has the same problem:</p> |
| |
| <div class="doc_code"><pre> |
| $ spiffygrep '-foo' test.txt |
| Unknown command line argument '-foo'. Try: spiffygrep --help' |
| |
| $ grep '-foo' test.txt |
| grep: illegal option -- f |
| grep: illegal option -- o |
| grep: illegal option -- o |
| Usage: grep -hblcnsviw pattern file . . . |
| </pre></div> |
| |
| <p>The solution for this problem is the same for both your tool and the system |
| version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on |
| the command line, it is telling the program that all options after the |
| '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we |
| can use it like this:</p> |
| |
| <div class="doc_code"><pre> |
| $ spiffygrep -- -foo test.txt |
| ...output... |
| </pre></div> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="getPosition">Determining absolute position with getPosition()</a> |
| </div> |
| <div class="doc_text"> |
| <p>Sometimes an option can affect or modify the meaning of another option. For |
| example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells |
| <tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force |
| the file to be interpreted as if it contained source code in language |
| <tt>LANG</tt>. In order to handle this properly , you need to know the |
| absolute position of each argument, especially those in lists, so their |
| interaction(s) can be applied correctly. This is also useful for options like |
| <tt>-llibname</tt> which is actually a positional argument that starts with |
| a dash.</p> |
| <p>So, generally, the problem is that you have two <tt>cl::list</tt> variables |
| that interact in some way. To ensure the correct interaction, you can use the |
| <tt>cl::list::getPosition(optnum)</tt> method. This method returns the |
| absolute position (as found on the command line) of the <tt>optnum</tt> |
| item in the <tt>cl::list</tt>.</p> |
| <p>The idiom for usage is like this:</p> |
| |
| <div class="doc_code"><pre> |
| static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); |
| static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore); |
| |
| int main(int argc, char**argv) { |
| // ... |
| std::vector<std::string>::iterator fileIt = Files.begin(); |
| std::vector<std::string>::iterator libIt = Libraries.begin(); |
| unsigned libPos = 0, filePos = 0; |
| while ( 1 ) { |
| if ( libIt != Libraries.end() ) |
| libPos = Libraries.getPosition( libIt - Libraries.begin() ); |
| else |
| libPos = 0; |
| if ( fileIt != Files.end() ) |
| filePos = Files.getPosition( fileIt - Files.begin() ); |
| else |
| filePos = 0; |
| |
| if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) { |
| // Source File Is next |
| ++fileIt; |
| } |
| else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) { |
| // Library is next |
| ++libIt; |
| } |
| else |
| break; // we're done with the list |
| } |
| }</pre></div> |
| |
| <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an |
| <tt>unsigned getPosition()</tt> option that will provide the absolute position |
| of that option. You can apply the same approach as above with a |
| <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p> |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is |
| used to construct programs that use "interpreter style" option processing. With |
| this style of option processing, all arguments specified after the last |
| positional argument are treated as special interpreter arguments that are not |
| interpreted by the command line argument.</p> |
| |
| <p>As a concrete example, lets say we are developing a replacement for the |
| standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first |
| you specify options to the shell itself (like <tt>-x</tt> which turns on trace |
| output), then you specify the name of the script to run, then you specify |
| arguments to the script. These arguments to the script are parsed by the bourne |
| shell command line option processor, but are not interpreted as options to the |
| shell itself. Using the CommandLine library, we would specify this as:</p> |
| |
| <div class="doc_code"><pre> |
| <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>("-")); |
| <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>")); |
| <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>")); |
| </pre></div> |
| |
| <p>which automatically provides the help output:</p> |
| |
| <div class="doc_code"><pre> |
| USAGE: spiffysh [options] <b><input script> <program arguments>...</b> |
| |
| OPTIONS: |
| -help - display available options (--help-hidden for more) |
| <b>-x - Enable trace output</b> |
| </pre></div> |
| |
| <p>At runtime, if we run our new shell replacement as `<tt>spiffysh -x test.sh |
| -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the |
| <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the |
| <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they |
| were specified after the last positional argument (which is the script |
| name).</p> |
| |
| <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can |
| be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified |
| per program, there must be at least one <a href="#positional">positional |
| argument</a> specified, there must not be any <a href="#cl::list">cl::list</a> |
| positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a |
| href="#cl::list">cl::list</a> option.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="storage">Internal vs External Storage</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>By default, all command line options automatically hold the value that they |
| parse from the command line. This is very convenient in the common case, |
| especially when combined with the ability to define command line options in the |
| files that use them. This is called the internal storage model.</p> |
| |
| <p>Sometimes, however, it is nice to separate the command line option processing |
| code from the storage of the value parsed. For example, lets say that we have a |
| '<tt>-debug</tt>' option that we would like to use to enable debug information |
| across the entire body of our program. In this case, the boolean value |
| controlling the debug code should be globally accessable (in a header file, for |
| example) yet the command line option processing code should not be exposed to |
| all of these clients (requiring lots of .cpp files to #include |
| <tt>CommandLine.h</tt>).</p> |
| |
| <p>To do this, set up your .h file with your option, like this for example:</p> |
| |
| <div class="doc_code"> |
| <pre> |
| <i>// DebugFlag.h - Get access to the '-debug' command line option |
| // |
| |
| // DebugFlag - This boolean is set to true if the '-debug' command line option |
| // is specified. This should probably not be referenced directly, instead, use |
| // the DEBUG macro below. |
| //</i> |
| extern bool DebugFlag; |
| |
| <i>// DEBUG macro - This macro should be used by code to emit debug information. |
| // In the '-debug' option is specified on the command line, and if this is a |
| // debug build, then the code specified as the option to the macro will be |
| // executed. Otherwise it will not be. Example: |
| // |
| // DEBUG(std::cerr << "Bitset contains: " << Bitset << "\n"); |
| //</i> |
| <span class="doc_hilite">#ifdef NDEBUG |
| #define DEBUG(X) |
| #else |
| #define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0) |
| <span class="doc_hilite">#endif</span> |
| </pre> |
| </div> |
| |
| <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the |
| <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to |
| set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass |
| an additial argument to our command line argument processor, and we specify |
| where to fill in with the <a href="#cl::location">cl::location</a> |
| attribute:</p> |
| |
| <div class="doc_code"> |
| <pre> |
| bool DebugFlag; <i>// the actual value</i> |
| static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i> |
| 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)); |
| </pre> |
| </div> |
| |
| <p>In the above example, we specify "<tt>true</tt>" as the second argument to |
| the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the |
| template should not maintain a copy of the value itself. In addition to this, |
| we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so |
| that <tt>DebugFlag</tt> is automatically set.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="attributes">Option Attributes</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>This section describes the basic attributes that you can specify on |
| options.</p> |
| |
| <ul> |
| |
| <li>The option name attribute (which is required for all options, except <a |
| href="#positional">positional options</a>) specifies what the option name is. |
| This option is specified in simple double quotes: |
| |
| <pre> |
| <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>"); |
| </pre> |
| |
| </li> |
| |
| <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a |
| description for the option to be shown in the <tt>--help</tt> output for the |
| program.</li> |
| |
| <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute |
| specifies a string that can be used to fine tune the <tt>--help</tt> output for |
| a command line option. Look <a href="#value_desc_example">here</a> for an |
| example.</li> |
| |
| <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an |
| inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is |
| not specified then the command line option value defaults to the value created |
| by the default constructor for the type. <b>Warning</b>: If you specify both |
| <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option, |
| you must specify <b><tt>cl::location</tt></b> first, so that when the |
| command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the |
| initial value. (You will get an error at runtime if you don't put them in |
| the right order.)</li> |
| |
| <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to |
| store the value for a parsed command line option if using external storage. See |
| the section on <a href="#storage">Internal vs External Storage</a> for more |
| information.</li> |
| |
| <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute |
| specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is |
| an alias for.</li> |
| |
| <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies |
| the string-to-value mapping to be used by the generic parser. It takes a |
| <b>clEnumValEnd terminated</b> list of (option, value, description) triplets |
| that |
| specify the option name, the value mapped to, and the description shown in the |
| <tt>--help</tt> for the tool. Because the generic parser is used most |
| frequently with enum values, two macros are often useful: |
| |
| <ol> |
| |
| <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a |
| nice simple way to specify a triplet for an enum. This macro automatically |
| makes the option name be the same as the enum name. The first option to the |
| macro is the enum, the second is the description for the command line |
| option.</li> |
| |
| <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to |
| specify macro options where the option name doesn't equal the enum name. For |
| this macro, the first argument is the enum value, the second is the flag name, |
| and the second is the description.</li> |
| |
| </ol> |
| |
| You will get a compile time error if you try to use cl::values with a parser |
| that does not support it.</li> |
| |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="modifiers">Option Modifiers</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Option modifiers are the flags and expressions that you pass into the |
| constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a |
| href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to |
| tweak how options are parsed and how <tt>--help</tt> output is generated to fit |
| your application well.</p> |
| |
| <p>These options fall into five main catagories:</p> |
| |
| <ol> |
| <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li> |
| <li><a href="#numoccurrences">Controlling the number of occurrences |
| required and allowed</a></li> |
| <li><a href="#valrequired">Controlling whether or not a value must be |
| specified</a></li> |
| <li><a href="#formatting">Controlling other formatting options</a></li> |
| <li><a href="#misc">Miscellaneous option modifiers</a></li> |
| </ol> |
| |
| <p>It is not possible to specify two options from the same catagory (you'll get |
| a runtime error) to a single option, except for options in the miscellaneous |
| catagory. The CommandLine library specifies defaults for all of these settings |
| that are the most useful in practice and the most common, which mean that you |
| usually shouldn't have to worry about these.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="hiding">Hiding an option from <tt>--help</tt> output</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and |
| <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option |
| appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the |
| compiled program:</p> |
| |
| <ul> |
| |
| <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier |
| (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a |
| href="#cl::list">cl::list</a></tt> options), indicates the option is to appear |
| in both help listings.</li> |
| |
| <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the |
| default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that |
| the option should not appear in the <tt>--help</tt> output, but should appear in |
| the <tt>--help-hidden</tt> output.</li> |
| |
| <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier, |
| indicates that the option should not appear in any help output.</li> |
| |
| </ul> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="numoccurrences">Controlling the number of occurrences required and |
| allowed</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>This group of options is used to control how many time an option is allowed |
| (or required) to be specified on the command line of your program. Specifying a |
| value for this setting allows the CommandLine library to do error checking for |
| you.</p> |
| |
| <p>The allowed values for this option group are:</p> |
| |
| <ul> |
| |
| <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which |
| is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a |
| href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will |
| allow either zero or one occurrence of the option to be specified.</li> |
| |
| <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier |
| (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class) |
| indicates that your program will allow the option to be specified zero or more |
| times.</li> |
| |
| <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier |
| indicates that the specified option must be specified exactly one time.</li> |
| |
| <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier |
| indicates that the option must be specified at least one time.</li> |
| |
| <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a |
| href="#positional">Positional arguments section</a></li> |
| |
| </ul> |
| |
| <p>If an option is not specified, then the value of the option is equal to the |
| value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If |
| the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the |
| option value is initialized with the default constructor for the data type.</p> |
| |
| <p>If an option is specified multiple times for an option of the <tt><a |
| href="#cl::opt">cl::opt</a></tt> class, only the last value will be |
| retained.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="valrequired">Controlling whether or not a value must be specified</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>This group of options is used to control whether or not the option allows a |
| value to be present. In the case of the CommandLine library, a value is either |
| specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing |
| string (e.g. '<tt>-o a.out</tt>').</p> |
| |
| <p>The allowed values for this option group are:</p> |
| |
| <ul> |
| |
| <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier |
| (which is the default for <tt>bool</tt> typed options) specifies that it is |
| acceptable to have a value, or not. A boolean argument can be enabled just by |
| appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'. |
| If an option is specified with this mode, it is illegal for the value to be |
| provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To |
| get this behavior, you must use the <a |
| href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li> |
| |
| <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier |
| (which is the default for all other types except for <a |
| href="#onealternative">unnamed alternatives using the generic parser</a>) |
| specifies that a value must be provided. This mode informs the command line |
| library that if an option is not provides with an equal sign, that the next |
| argument provided must be the value. This allows things like '<tt>-o |
| a.out</tt>' to work.</li> |
| |
| <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a> |
| modifier (which is the default for <a href="#onealternative">unnamed |
| alternatives using the generic parser</a>) indicates that it is a runtime error |
| for the user to specify a value. This can be provided to disallow users from |
| providing options to boolean options (like '<tt>-foo=true</tt>').</li> |
| |
| </ul> |
| |
| <p>In general, the default values for this option group work just like you would |
| want them to. As mentioned above, you can specify the <a |
| href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean |
| argument to restrict your command line parser. These options are mostly useful |
| when <a href="#extensionguide">extending the library</a>.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="formatting">Controlling other formatting options</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The formatting option group is used to specify that the command line option |
| has special abilities and is otherwise different from other command line |
| arguments. As usual, you can only specify at most one of these arguments.</p> |
| |
| <ul> |
| |
| <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a> |
| modifier (which is the default all options) specifies that this option is |
| "normal".</li> |
| |
| <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier |
| specifies that this is a positional argument, that does not have a command line |
| option associated with it. See the <a href="#positional">Positional |
| Arguments</a> section for more information.</li> |
| |
| <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier |
| specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li> |
| |
| <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies |
| that this option prefixes its value. With 'Prefix' options, the equal sign does |
| not separate the value from the option name specified. Instead, the value is |
| everything after the prefix, including any equal sign if present. This is useful |
| for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a |
| linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the |
| '<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list) |
| options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to |
| allow the CommandLine library to recognize them. Note that |
| <a href="#cl::Prefix">cl::Prefix</a> options must not have the <a |
| href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li> |
| |
| <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used |
| to implement unix style tools (like <tt>ls</tt>) that have lots of single letter |
| arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>' |
| command actually enables four different options, all of which are single |
| letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have |
| values.</li> |
| |
| </ul> |
| |
| <p>The CommandLine library does not restrict how you use the <a |
| href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a> |
| modifiers, but it is possible to specify ambiguous argument settings. Thus, it |
| is possible to have multiple letter options that are prefix or grouping options, |
| and they will still work as designed.</p> |
| |
| <p>To do this, the CommandLine library uses a greedy algorithm to parse the |
| input option into (potentially multiple) prefix and grouping options. The |
| strategy basically looks like this:</p> |
| |
| <div class="doc_code"><tt>parse(string OrigInput) {</tt> |
| |
| <ol> |
| <li><tt>string input = OrigInput;</tt> |
| <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i> |
| <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i> |
| <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i> |
| <li><tt>if (getOption(input).isPrefix())<br> |
| return getOption(input).parse(input);</tt> |
| <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br> |
| getOption(input).parse();<br> |
| OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br> |
| input = OrigInput;<br> |
| while (!isOption(input) && !input.empty()) input.pop_back();<br> |
| }</tt> |
| <li><tt>if (!OrigInput.empty()) error();</tt></li> |
| </ol> |
| |
| <p><tt>}</tt></p> |
| </div> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="misc">Miscellaneous option modifiers</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The miscellaneous option modifiers are the only flags where you can specify |
| more than one flag from the set: they are not mutually exclusive. These flags |
| specify boolean properties that modify the option.</p> |
| |
| <ul> |
| |
| <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier |
| indicates that any commas specified for an option's value should be used to |
| split the value up into multiple values for the option. For example, these two |
| options are equivalent when <tt>cl::CommaSeparated</tt> is specified: |
| "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only |
| makes sense to be used in a case where the option is allowed to accept one or |
| more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li> |
| |
| <li><a name="cl::PositionalEatsArgs">The |
| <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to |
| positional arguments, and only makes sense for lists) indicates that positional |
| argument should consume any strings after it (including strings that start with |
| a "-") up until another recognized positional argument. For example, if you |
| have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the |
| string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar |
| -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the |
| "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li> |
| |
| </ul> |
| |
| <p>So far, these are the only two miscellaneous option modifiers.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="toplevel">Top-Level Classes and Functions</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Despite all of the built-in flexibility, the CommandLine option library |
| really only consists of one function (<a |
| href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>) |
| and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a |
| href="#cl::list"><tt>cl::list</tt></a>, and <a |
| href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three |
| classes in detail.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt> |
| function</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called |
| directly from <tt>main</tt>, and is used to fill in the values of all of the |
| command line option variables once <tt>argc</tt> and <tt>argv</tt> are |
| available.</p> |
| |
| <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters |
| (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter |
| which holds <a href="#description">additional extra text</a> to emit when the |
| <tt>--help</tt> option is invoked.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt> |
| function</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects |
| as <a |
| href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>, |
| except that it is designed to take values for options from an environment |
| variable, for those cases in which reading the command line is not convenient or |
| not desired. It fills in the values of all the command line option variables |
| just like <a |
| href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> |
| does.</p> |
| |
| <p>It takes three parameters: first, the name of the program (since |
| <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>), |
| second, the name of the environment variable to examine, and third, the optional |
| <a href="#description">additional extra text</a> to emit when the |
| <tt>--help</tt> option is invoked.</p> |
| |
| <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment |
| variable's value up into words and then process them using |
| <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>. |
| <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support |
| quoting, so an environment variable containing <tt>-option "foo bar"</tt> will |
| be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>, |
| which is different from what you would get from the shell with the same |
| input.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::opt">The <tt>cl::opt</tt> class</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line |
| options, and is the one used most of the time. It is a templated class which |
| can take up to three arguments (all except for the first have default values |
| though):</p> |
| |
| <div class="doc_code"><pre> |
| <b>namespace</b> cl { |
| <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>, |
| <b>class</b> ParserClass = parser<DataType> > |
| <b>class</b> opt; |
| } |
| </pre></div> |
| |
| <p>The first template argument specifies what underlying data type the command |
| line argument is, and is used to select a default parser implementation. The |
| second template argument is used to specify whether the option should contain |
| the storage for the option (the default) or whether external storage should be |
| used to contain the value parsed for the option (see <a href="#storage">Internal |
| vs External Storage</a> for more information).</p> |
| |
| <p>The third template argument specifies which parser to use. The default value |
| selects an instantiation of the <tt>parser</tt> class based on the underlying |
| data type of the option. In general, this default works well for most |
| applications, so this option is only used when using a <a |
| href="#customparser">custom parser</a>.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::list">The <tt>cl::list</tt> class</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::list</tt> class is the class used to represent a list of command |
| line options. It too is a templated class which can take up to three |
| arguments:</p> |
| |
| <div class="doc_code"><pre> |
| <b>namespace</b> cl { |
| <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, |
| <b>class</b> ParserClass = parser<DataType> > |
| <b>class</b> list; |
| } |
| </pre></div> |
| |
| <p>This class works the exact same as the <a |
| href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is |
| the <b>type</b> of the external storage, not a boolean value. For this class, |
| the marker type '<tt>bool</tt>' is used to indicate that internal storage should |
| be used.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::alias">The <tt>cl::alias</tt> class</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form |
| aliases for other arguments.</p> |
| |
| <div class="doc_code"><pre> |
| <b>namespace</b> cl { |
| <b>class</b> alias; |
| } |
| </pre></div> |
| |
| <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be |
| used to specify which option this is an alias for. Alias arguments default to |
| being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do |
| the conversion from string to data.</p> |
| |
| </div> |
| |
| <!-- _______________________________________________________________________ --> |
| <div class="doc_subsubsection"> |
| <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra |
| help text to be printed out for the <tt>--help</tt> option.</p> |
| |
| <div class="doc_code"><pre> |
| <b>namespace</b> cl { |
| <b>struct</b> extrahelp; |
| } |
| </pre></div> |
| |
| <p>To use the extrahelp, simply construct one with a <tt>const char*</tt> |
| parameter to the constructor. The text passed to the constructor will be printed |
| at the bottom of the help message, verbatim. Note that multiple |
| <tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If |
| your tool needs to print additional help information, put all that help into a |
| single <tt>cl::extrahelp</tt> instance.</p> |
| <p>For example:</p> |
| <div class="doc_code"><pre> |
| cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); |
| </pre></div> |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="builtinparsers">Builtin parsers</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>Parsers control how the string value taken from the command line is |
| translated into a typed value, suitable for use in a C++ program. By default, |
| the CommandLine library uses an instance of <tt>parser<type></tt> if the |
| command line option specifies that it uses values of type '<tt>type</tt>'. |
| Because of this, custom option processing is specified with specializations of |
| the '<tt>parser</tt>' class.</p> |
| |
| <p>The CommandLine library provides the following builtin parser |
| specializations, which are sufficient for most applications. It can, however, |
| also be extended to work with new data types and new ways of interpreting the |
| same data. See the <a href="#customparser">Writing a Custom Parser</a> for more |
| details on this type of library extension.</p> |
| |
| <ul> |
| |
| <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a> |
| can be used to map strings values to any data type, through the use of the <a |
| href="#cl::values">cl::values</a> property, which specifies the mapping |
| information. The most common use of this parser is for parsing enum values, |
| which allows you to use the CommandLine library for all of the error checking to |
| make sure that only valid enum values are specified (as opposed to accepting |
| arbitrary strings). Despite this, however, the generic parser class can be used |
| for any data type.</li> |
| |
| <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a> |
| is used to convert boolean strings to a boolean value. Currently accepted |
| strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>", |
| "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li> |
| |
| <li><a name="stringparser">The <b><tt>parser<string></tt> |
| specialization</b></a> simply stores the parsed string into the string value |
| specified. No conversion or modification of the data is performed.</li> |
| |
| <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a> |
| uses the C <tt>strtol</tt> function to parse the string input. As such, it will |
| accept a decimal number (with an optional '+' or '-' prefix) which must start |
| with a non-zero digit. It accepts octal numbers, which are identified with a |
| '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of |
| '<tt>0x</tt>' or '<tt>0X</tt>'.</li> |
| |
| <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and |
| <b><tt>parser<float></tt> specializations</b> use the standard C |
| <tt>strtod</tt> function to convert floating point strings into floating point |
| values. As such, a broad range of string formats is supported, including |
| exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales. |
| </li> |
| |
| </ul> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="extensionguide">Extension Guide</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>Although the CommandLine library has a lot of functionality built into it |
| already (as discussed previously), one of its true strengths lie in its |
| extensibility. This section discusses how the CommandLine library works under |
| the covers and illustrates how to do some simple, common, extensions.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="customparser">Writing a custom parser</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>One of the simplest and most common extensions is the use of a custom parser. |
| As <a href="#builtinparsers">discussed previously</a>, parsers are the portion |
| of the CommandLine library that turns string input from the user into a |
| particular parsed data type, validating the input in the process.</p> |
| |
| <p>There are two ways to use a new parser:</p> |
| |
| <ol> |
| |
| <li> |
| |
| <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for |
| your custom data type.<p> |
| |
| <p>This approach has the advantage that users of your custom data type will |
| automatically use your custom parser whenever they define an option with a value |
| type of your data type. The disadvantage of this approach is that it doesn't |
| work if your fundemental data type is something that is already supported.</p> |
| |
| </li> |
| |
| <li> |
| |
| <p>Write an independent class, using it explicitly from options that need |
| it.</p> |
| |
| <p>This approach works well in situations where you would line to parse an |
| option using special syntax for a not-very-special data-type. The drawback of |
| this approach is that users of your parser have to be aware that they are using |
| your parser, instead of the builtin ones.</p> |
| |
| </li> |
| |
| </ol> |
| |
| <p>To guide the discussion, we will discuss a custom parser that accepts file |
| sizes, specified with an optional unit after the numeric size. For example, we |
| would like to parse "102kb", "41M", "1G" into the appropriate integer value. In |
| this case, the underlying data type we want to parse into is |
| '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make |
| this the default for all <tt>unsigned</tt> options.</p> |
| |
| <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p> |
| |
| <div class="doc_code"><pre> |
| <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> { |
| <i>// parse - Return true on error.</i> |
| <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue, |
| <b>unsigned</b> &Val); |
| }; |
| </pre></div> |
| |
| <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to |
| fill in the default, boiler plate, code for us. We give it the data type that |
| we parse into (the last argument to the <tt>parse</tt> method so that clients of |
| our custom parser know what object type to pass in to the parse method (here we |
| declare that we parse into '<tt>unsigned</tt>' variables.</p> |
| |
| <p>For most purposes, the only method that must be implemented in a custom |
| parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called |
| whenever the option is invoked, passing in the option itself, the option name, |
| the string to parse, and a reference to a return value. If the string to parse |
| is not well formed, the parser should output an error message and return true. |
| Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In |
| our example, we implement <tt>parse</tt> as:</p> |
| |
| <div class="doc_code"><pre> |
| <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName, |
| <b>const</b> std::string &Arg, <b>unsigned</b> &Val) { |
| <b>const char</b> *ArgStart = Arg.c_str(); |
| <b>char</b> *End; |
| |
| <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i> |
| Val = (unsigned)strtol(ArgStart, &End, 0); |
| |
| <b>while</b> (1) { |
| <b>switch</b> (*End++) { |
| <b>case</b> 0: <b>return</b> false; <i>// No error</i> |
| <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i> |
| <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i> |
| <b>break</b>; |
| |
| <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>; |
| <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>; |
| <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>; |
| |
| default: |
| <i>// Print an error message if unrecognized character!</i> |
| <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!"); |
| } |
| } |
| } |
| </pre></div> |
| |
| <p>This function implements a very simple parser for the kinds of strings we are |
| interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for |
| example), it is good enough for this example. Note that we use the option |
| itself to print out the error message (the <tt>error</tt> method always returns |
| true) in order to get a nice error message (shown below). Now that we have our |
| parser class, we can use it like this:</p> |
| |
| <div class="doc_code"><pre> |
| <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser> |
| MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>), |
| <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>")); |
| </pre></div> |
| |
| <p>Which adds this to the output of our program:</p> |
| |
| <div class="doc_code"><pre> |
| OPTIONS: |
| -help - display available options (--help-hidden for more) |
| ... |
| <b>-max-file-size=<size> - Maximum file size to accept</b> |
| </pre></div> |
| |
| <p>And we can test that our parse works correctly now (the test program just |
| prints out the max-file-size argument value):</p> |
| |
| <div class="doc_code"><pre> |
| $ ./test |
| MFS: 0 |
| $ ./test -max-file-size=123MB |
| MFS: 128974848 |
| $ ./test -max-file-size=3G |
| MFS: 3221225472 |
| $ ./test -max-file-size=dog |
| -max-file-size option: 'dog' value invalid for file size argument! |
| </pre></div> |
| |
| <p>It looks like it works. The error message that we get is nice and helpful, |
| and we seem to accept reasonable file sizes. This wraps up the "custom parser" |
| tutorial.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="explotingexternal">Exploiting external storage</a> |
| </div> |
| |
| <div class="doc_text"> |
| <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that |
| will automatically be included in any program that links with that library. |
| This is a feature. However, sometimes it is necessary to know the value of the |
| command line option outside of the library. In these cases the library does or |
| should provide an external storage location that is accessible to users of the |
| library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the |
| <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt> |
| flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p> |
| |
| <p>TODO: complete this section</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="dynamicopts">Dynamically adding command line options</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <p>TODO: fill in this section</p> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| |
| <hr> |
| <address> |
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| |
| <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> |
| <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br> |
| Last modified: $Date$ |
| </address> |
| |
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