| Dan Gohman | f17a25c | 2007-07-18 16:29:46 +0000 | [diff] [blame^] | 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" |
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| 6 | <title>CommandLine 2.0 Library Manual</title> |
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| 8 | </head> |
| 9 | <body> |
| 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> |
| 47 | <li><a href="#hiding">Hiding an option from <tt>--help</tt> |
| 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> |
| 59 | <li><a href="#cl::ParseCommandLineOptions">The |
| 60 | <tt>cl::ParseCommandLineOptions</tt> function</a></li> |
| 61 | <li><a href="#cl::ParseEnvironmentOptions">The |
| 62 | <tt>cl::ParseEnvironmentOptions</tt> function</a></li> |
| 63 | <li><a href="#cl::SetVersionPrinter">The cl::SetVersionPrinter |
| 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> |
| 92 | <li><a href="#dynamicopts">Dynamically adding command line |
| 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 |
| 141 | because the application doesn't have to keep a "list" of arguments to pass to |
| 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 |
| 219 | system which ones we want, and what type of argument they are. The CommandLine |
| 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, |
| 224 | we would like to support the unix standard '<tt>-o <filename></tt>' option |
| 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 | ... |
| 259 | ofstream Output(OutputFilename.c_str()); |
| 260 | if (Out.good()) ... |
| 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 | |
| 386 | <p>and "<tt>opt --help-hidden</tt>" prints this:</p> |
| 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 |
| 435 | "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by |
| 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 | |
| 465 | <p>So far, we have seen how the CommandLine library handles builtin types like |
| 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 | |
| 469 | <p>The answer is that it uses a table driven generic parser (unless you specify |
| 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 | |
| 474 | <p>Lets say that we would like to add four optimization levels to our |
| 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, |
| 481 | "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this |
| 482 | erroneous input for us.</li> |
| 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 |
| 516 | terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine |
| 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 | |
| 637 | <p>Now that we have the standard run of the mill argument types out of the way, |
| 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 |
| 753 | href="#bits"><tt>cl::bits</tt></a> option is morally equivalent to a <a |
| 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 |
| 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 |
| 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> |
| 916 | |
| 917 | <div class="doc_code"><pre> |
| 918 | static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); |
| 919 | static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore); |
| 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 |
| 951 | of that option. You can apply the same approach as above with a |
| 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 |
| 972 | arguments to the script. These arguments to the script are parsed by the bourne |
| 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 |
| 1045 | // executed. Otherwise it will not be. Example: |
| 1046 | // |
| 1047 | // DOUT << "Bitset contains: " << Bitset << "\n"; |
| 1048 | //</i> |
| 1049 | <span class="doc_hilite">#ifdef NDEBUG |
| 1050 | #define DEBUG(X) |
| 1051 | #else |
| 1052 | #define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0) |
| 1053 | <span class="doc_hilite">#endif</span> |
| 1054 | </pre> |
| 1055 | </div> |
| 1056 | |
| 1057 | <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the |
| 1058 | <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to |
| 1059 | set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass |
| 1060 | an additial argument to our command line argument processor, and we specify |
| 1061 | where to fill in with the <a href="#cl::location">cl::location</a> |
| 1062 | attribute:</p> |
| 1063 | |
| 1064 | <div class="doc_code"> |
| 1065 | <pre> |
| 1066 | bool DebugFlag; <i>// the actual value</i> |
| 1067 | static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i> |
| 1068 | 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)); |
| 1069 | </pre> |
| 1070 | </div> |
| 1071 | |
| 1072 | <p>In the above example, we specify "<tt>true</tt>" as the second argument to |
| 1073 | the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the |
| 1074 | template should not maintain a copy of the value itself. In addition to this, |
| 1075 | we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so |
| 1076 | that <tt>DebugFlag</tt> is automatically set.</p> |
| 1077 | |
| 1078 | </div> |
| 1079 | |
| 1080 | <!-- ======================================================================= --> |
| 1081 | <div class="doc_subsection"> |
| 1082 | <a name="attributes">Option Attributes</a> |
| 1083 | </div> |
| 1084 | |
| 1085 | <div class="doc_text"> |
| 1086 | |
| 1087 | <p>This section describes the basic attributes that you can specify on |
| 1088 | options.</p> |
| 1089 | |
| 1090 | <ul> |
| 1091 | |
| 1092 | <li>The option name attribute (which is required for all options, except <a |
| 1093 | href="#positional">positional options</a>) specifies what the option name is. |
| 1094 | This option is specified in simple double quotes: |
| 1095 | |
| 1096 | <pre> |
| 1097 | <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>"); |
| 1098 | </pre> |
| 1099 | |
| 1100 | </li> |
| 1101 | |
| 1102 | <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a |
| 1103 | description for the option to be shown in the <tt>--help</tt> output for the |
| 1104 | program.</li> |
| 1105 | |
| 1106 | <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute |
| 1107 | specifies a string that can be used to fine tune the <tt>--help</tt> output for |
| 1108 | a command line option. Look <a href="#value_desc_example">here</a> for an |
| 1109 | example.</li> |
| 1110 | |
| 1111 | <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an |
| 1112 | inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is |
| 1113 | not specified then the command line option value defaults to the value created |
| 1114 | by the default constructor for the type. <b>Warning</b>: If you specify both |
| 1115 | <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option, |
| 1116 | you must specify <b><tt>cl::location</tt></b> first, so that when the |
| 1117 | command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the |
| 1118 | initial value. (You will get an error at runtime if you don't put them in |
| 1119 | the right order.)</li> |
| 1120 | |
| 1121 | <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to |
| 1122 | store the value for a parsed command line option if using external storage. See |
| 1123 | the section on <a href="#storage">Internal vs External Storage</a> for more |
| 1124 | information.</li> |
| 1125 | |
| 1126 | <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute |
| 1127 | specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is |
| 1128 | an alias for.</li> |
| 1129 | |
| 1130 | <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies |
| 1131 | the string-to-value mapping to be used by the generic parser. It takes a |
| 1132 | <b>clEnumValEnd terminated</b> list of (option, value, description) triplets |
| 1133 | that |
| 1134 | specify the option name, the value mapped to, and the description shown in the |
| 1135 | <tt>--help</tt> for the tool. Because the generic parser is used most |
| 1136 | frequently with enum values, two macros are often useful: |
| 1137 | |
| 1138 | <ol> |
| 1139 | |
| 1140 | <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a |
| 1141 | nice simple way to specify a triplet for an enum. This macro automatically |
| 1142 | makes the option name be the same as the enum name. The first option to the |
| 1143 | macro is the enum, the second is the description for the command line |
| 1144 | option.</li> |
| 1145 | |
| 1146 | <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to |
| 1147 | specify macro options where the option name doesn't equal the enum name. For |
| 1148 | this macro, the first argument is the enum value, the second is the flag name, |
| 1149 | and the second is the description.</li> |
| 1150 | |
| 1151 | </ol> |
| 1152 | |
| 1153 | You will get a compile time error if you try to use cl::values with a parser |
| 1154 | that does not support it.</li> |
| 1155 | |
| 1156 | </ul> |
| 1157 | |
| 1158 | </div> |
| 1159 | |
| 1160 | <!-- ======================================================================= --> |
| 1161 | <div class="doc_subsection"> |
| 1162 | <a name="modifiers">Option Modifiers</a> |
| 1163 | </div> |
| 1164 | |
| 1165 | <div class="doc_text"> |
| 1166 | |
| 1167 | <p>Option modifiers are the flags and expressions that you pass into the |
| 1168 | constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a |
| 1169 | href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to |
| 1170 | tweak how options are parsed and how <tt>--help</tt> output is generated to fit |
| 1171 | your application well.</p> |
| 1172 | |
| 1173 | <p>These options fall into five main catagories:</p> |
| 1174 | |
| 1175 | <ol> |
| 1176 | <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li> |
| 1177 | <li><a href="#numoccurrences">Controlling the number of occurrences |
| 1178 | required and allowed</a></li> |
| 1179 | <li><a href="#valrequired">Controlling whether or not a value must be |
| 1180 | specified</a></li> |
| 1181 | <li><a href="#formatting">Controlling other formatting options</a></li> |
| 1182 | <li><a href="#misc">Miscellaneous option modifiers</a></li> |
| 1183 | </ol> |
| 1184 | |
| 1185 | <p>It is not possible to specify two options from the same catagory (you'll get |
| 1186 | a runtime error) to a single option, except for options in the miscellaneous |
| 1187 | catagory. The CommandLine library specifies defaults for all of these settings |
| 1188 | that are the most useful in practice and the most common, which mean that you |
| 1189 | usually shouldn't have to worry about these.</p> |
| 1190 | |
| 1191 | </div> |
| 1192 | |
| 1193 | <!-- _______________________________________________________________________ --> |
| 1194 | <div class="doc_subsubsection"> |
| 1195 | <a name="hiding">Hiding an option from <tt>--help</tt> output</a> |
| 1196 | </div> |
| 1197 | |
| 1198 | <div class="doc_text"> |
| 1199 | |
| 1200 | <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and |
| 1201 | <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option |
| 1202 | appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the |
| 1203 | compiled program:</p> |
| 1204 | |
| 1205 | <ul> |
| 1206 | |
| 1207 | <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier |
| 1208 | (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a |
| 1209 | href="#cl::list">cl::list</a></tt> options), indicates the option is to appear |
| 1210 | in both help listings.</li> |
| 1211 | |
| 1212 | <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the |
| 1213 | default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that |
| 1214 | the option should not appear in the <tt>--help</tt> output, but should appear in |
| 1215 | the <tt>--help-hidden</tt> output.</li> |
| 1216 | |
| 1217 | <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier, |
| 1218 | indicates that the option should not appear in any help output.</li> |
| 1219 | |
| 1220 | </ul> |
| 1221 | |
| 1222 | </div> |
| 1223 | |
| 1224 | <!-- _______________________________________________________________________ --> |
| 1225 | <div class="doc_subsubsection"> |
| 1226 | <a name="numoccurrences">Controlling the number of occurrences required and |
| 1227 | allowed</a> |
| 1228 | </div> |
| 1229 | |
| 1230 | <div class="doc_text"> |
| 1231 | |
| 1232 | <p>This group of options is used to control how many time an option is allowed |
| 1233 | (or required) to be specified on the command line of your program. Specifying a |
| 1234 | value for this setting allows the CommandLine library to do error checking for |
| 1235 | you.</p> |
| 1236 | |
| 1237 | <p>The allowed values for this option group are:</p> |
| 1238 | |
| 1239 | <ul> |
| 1240 | |
| 1241 | <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which |
| 1242 | is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a |
| 1243 | href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will |
| 1244 | allow either zero or one occurrence of the option to be specified.</li> |
| 1245 | |
| 1246 | <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier |
| 1247 | (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class) |
| 1248 | indicates that your program will allow the option to be specified zero or more |
| 1249 | times.</li> |
| 1250 | |
| 1251 | <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier |
| 1252 | indicates that the specified option must be specified exactly one time.</li> |
| 1253 | |
| 1254 | <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier |
| 1255 | indicates that the option must be specified at least one time.</li> |
| 1256 | |
| 1257 | <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a |
| 1258 | href="#positional">Positional arguments section</a></li> |
| 1259 | |
| 1260 | </ul> |
| 1261 | |
| 1262 | <p>If an option is not specified, then the value of the option is equal to the |
| 1263 | value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If |
| 1264 | the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the |
| 1265 | option value is initialized with the default constructor for the data type.</p> |
| 1266 | |
| 1267 | <p>If an option is specified multiple times for an option of the <tt><a |
| 1268 | href="#cl::opt">cl::opt</a></tt> class, only the last value will be |
| 1269 | retained.</p> |
| 1270 | |
| 1271 | </div> |
| 1272 | |
| 1273 | <!-- _______________________________________________________________________ --> |
| 1274 | <div class="doc_subsubsection"> |
| 1275 | <a name="valrequired">Controlling whether or not a value must be specified</a> |
| 1276 | </div> |
| 1277 | |
| 1278 | <div class="doc_text"> |
| 1279 | |
| 1280 | <p>This group of options is used to control whether or not the option allows a |
| 1281 | value to be present. In the case of the CommandLine library, a value is either |
| 1282 | specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing |
| 1283 | string (e.g. '<tt>-o a.out</tt>').</p> |
| 1284 | |
| 1285 | <p>The allowed values for this option group are:</p> |
| 1286 | |
| 1287 | <ul> |
| 1288 | |
| 1289 | <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier |
| 1290 | (which is the default for <tt>bool</tt> typed options) specifies that it is |
| 1291 | acceptable to have a value, or not. A boolean argument can be enabled just by |
| 1292 | appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'. |
| 1293 | If an option is specified with this mode, it is illegal for the value to be |
| 1294 | provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To |
| 1295 | get this behavior, you must use the <a |
| 1296 | href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li> |
| 1297 | |
| 1298 | <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier |
| 1299 | (which is the default for all other types except for <a |
| 1300 | href="#onealternative">unnamed alternatives using the generic parser</a>) |
| 1301 | specifies that a value must be provided. This mode informs the command line |
| 1302 | library that if an option is not provides with an equal sign, that the next |
| 1303 | argument provided must be the value. This allows things like '<tt>-o |
| 1304 | a.out</tt>' to work.</li> |
| 1305 | |
| 1306 | <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a> |
| 1307 | modifier (which is the default for <a href="#onealternative">unnamed |
| 1308 | alternatives using the generic parser</a>) indicates that it is a runtime error |
| 1309 | for the user to specify a value. This can be provided to disallow users from |
| 1310 | providing options to boolean options (like '<tt>-foo=true</tt>').</li> |
| 1311 | |
| 1312 | </ul> |
| 1313 | |
| 1314 | <p>In general, the default values for this option group work just like you would |
| 1315 | want them to. As mentioned above, you can specify the <a |
| 1316 | href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean |
| 1317 | argument to restrict your command line parser. These options are mostly useful |
| 1318 | when <a href="#extensionguide">extending the library</a>.</p> |
| 1319 | |
| 1320 | </div> |
| 1321 | |
| 1322 | <!-- _______________________________________________________________________ --> |
| 1323 | <div class="doc_subsubsection"> |
| 1324 | <a name="formatting">Controlling other formatting options</a> |
| 1325 | </div> |
| 1326 | |
| 1327 | <div class="doc_text"> |
| 1328 | |
| 1329 | <p>The formatting option group is used to specify that the command line option |
| 1330 | has special abilities and is otherwise different from other command line |
| 1331 | arguments. As usual, you can only specify at most one of these arguments.</p> |
| 1332 | |
| 1333 | <ul> |
| 1334 | |
| 1335 | <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a> |
| 1336 | modifier (which is the default all options) specifies that this option is |
| 1337 | "normal".</li> |
| 1338 | |
| 1339 | <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier |
| 1340 | specifies that this is a positional argument, that does not have a command line |
| 1341 | option associated with it. See the <a href="#positional">Positional |
| 1342 | Arguments</a> section for more information.</li> |
| 1343 | |
| 1344 | <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier |
| 1345 | specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li> |
| 1346 | |
| 1347 | <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies |
| 1348 | that this option prefixes its value. With 'Prefix' options, the equal sign does |
| 1349 | not separate the value from the option name specified. Instead, the value is |
| 1350 | everything after the prefix, including any equal sign if present. This is useful |
| 1351 | for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a |
| 1352 | linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the |
| 1353 | '<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list) |
| 1354 | options, that have the <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> |
| 1355 | modifier added to allow the CommandLine library to recognize them. Note that |
| 1356 | <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> options must not have the |
| 1357 | <b><tt><a href="#cl::ValueDisallowed">cl::ValueDisallowed</a></tt></b> modifier |
| 1358 | specified.</li> |
| 1359 | |
| 1360 | <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used |
| 1361 | to implement unix style tools (like <tt>ls</tt>) that have lots of single letter |
| 1362 | arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>' |
| 1363 | command actually enables four different options, all of which are single |
| 1364 | letters. Note that <b><tt><a href="#cl::Grouping">cl::Grouping</a></tt></b> |
| 1365 | options cannot have values.</li> |
| 1366 | |
| 1367 | </ul> |
| 1368 | |
| 1369 | <p>The CommandLine library does not restrict how you use the <b><tt><a |
| 1370 | href="#cl::Prefix">cl::Prefix</a></tt></b> or <b><tt><a |
| 1371 | href="#cl::Grouping">cl::Grouping</a></tt></b> modifiers, but it is possible to |
| 1372 | specify ambiguous argument settings. Thus, it is possible to have multiple |
| 1373 | letter options that are prefix or grouping options, and they will still work as |
| 1374 | designed.</p> |
| 1375 | |
| 1376 | <p>To do this, the CommandLine library uses a greedy algorithm to parse the |
| 1377 | input option into (potentially multiple) prefix and grouping options. The |
| 1378 | strategy basically looks like this:</p> |
| 1379 | |
| 1380 | <div class="doc_code"><tt>parse(string OrigInput) {</tt> |
| 1381 | |
| 1382 | <ol> |
| 1383 | <li><tt>string input = OrigInput;</tt> |
| 1384 | <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i> |
| 1385 | <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i> |
| 1386 | <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i> |
| 1387 | <li><tt>if (getOption(input).isPrefix())<br> |
| 1388 | return getOption(input).parse(input);</tt> |
| 1389 | <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br> |
| 1390 | getOption(input).parse();<br> |
| 1391 | OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br> |
| 1392 | input = OrigInput;<br> |
| 1393 | while (!isOption(input) && !input.empty()) input.pop_back();<br> |
| 1394 | }</tt> |
| 1395 | <li><tt>if (!OrigInput.empty()) error();</tt></li> |
| 1396 | </ol> |
| 1397 | |
| 1398 | <p><tt>}</tt></p> |
| 1399 | </div> |
| 1400 | |
| 1401 | </div> |
| 1402 | |
| 1403 | <!-- _______________________________________________________________________ --> |
| 1404 | <div class="doc_subsubsection"> |
| 1405 | <a name="misc">Miscellaneous option modifiers</a> |
| 1406 | </div> |
| 1407 | |
| 1408 | <div class="doc_text"> |
| 1409 | |
| 1410 | <p>The miscellaneous option modifiers are the only flags where you can specify |
| 1411 | more than one flag from the set: they are not mutually exclusive. These flags |
| 1412 | specify boolean properties that modify the option.</p> |
| 1413 | |
| 1414 | <ul> |
| 1415 | |
| 1416 | <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier |
| 1417 | indicates that any commas specified for an option's value should be used to |
| 1418 | split the value up into multiple values for the option. For example, these two |
| 1419 | options are equivalent when <tt>cl::CommaSeparated</tt> is specified: |
| 1420 | "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only |
| 1421 | makes sense to be used in a case where the option is allowed to accept one or |
| 1422 | more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li> |
| 1423 | |
| 1424 | <li><a name="cl::PositionalEatsArgs">The |
| 1425 | <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to |
| 1426 | positional arguments, and only makes sense for lists) indicates that positional |
| 1427 | argument should consume any strings after it (including strings that start with |
| 1428 | a "-") up until another recognized positional argument. For example, if you |
| 1429 | have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the |
| 1430 | string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar |
| 1431 | -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the |
| 1432 | "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li> |
| 1433 | |
| 1434 | </ul> |
| 1435 | |
| 1436 | <p>So far, these are the only two miscellaneous option modifiers.</p> |
| 1437 | |
| 1438 | </div> |
| 1439 | |
| 1440 | <!-- ======================================================================= --> |
| 1441 | <div class="doc_subsection"> |
| 1442 | <a name="toplevel">Top-Level Classes and Functions</a> |
| 1443 | </div> |
| 1444 | |
| 1445 | <div class="doc_text"> |
| 1446 | |
| 1447 | <p>Despite all of the built-in flexibility, the CommandLine option library |
| 1448 | really only consists of one function (<a |
| 1449 | href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>) |
| 1450 | and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a |
| 1451 | href="#cl::list"><tt>cl::list</tt></a>, and <a |
| 1452 | href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three |
| 1453 | classes in detail.</p> |
| 1454 | |
| 1455 | </div> |
| 1456 | |
| 1457 | <!-- _______________________________________________________________________ --> |
| 1458 | <div class="doc_subsubsection"> |
| 1459 | <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt> |
| 1460 | function</a> |
| 1461 | </div> |
| 1462 | |
| 1463 | <div class="doc_text"> |
| 1464 | |
| 1465 | <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called |
| 1466 | directly from <tt>main</tt>, and is used to fill in the values of all of the |
| 1467 | command line option variables once <tt>argc</tt> and <tt>argv</tt> are |
| 1468 | available.</p> |
| 1469 | |
| 1470 | <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters |
| 1471 | (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter |
| 1472 | which holds <a href="#description">additional extra text</a> to emit when the |
| 1473 | <tt>--help</tt> option is invoked.</p> |
| 1474 | |
| 1475 | </div> |
| 1476 | |
| 1477 | <!-- _______________________________________________________________________ --> |
| 1478 | <div class="doc_subsubsection"> |
| 1479 | <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt> |
| 1480 | function</a> |
| 1481 | </div> |
| 1482 | |
| 1483 | <div class="doc_text"> |
| 1484 | |
| 1485 | <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects |
| 1486 | as <a |
| 1487 | href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>, |
| 1488 | except that it is designed to take values for options from an environment |
| 1489 | variable, for those cases in which reading the command line is not convenient or |
| 1490 | not desired. It fills in the values of all the command line option variables |
| 1491 | just like <a |
| 1492 | href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> |
| 1493 | does.</p> |
| 1494 | |
| 1495 | <p>It takes three parameters: first, the name of the program (since |
| 1496 | <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>), |
| 1497 | second, the name of the environment variable to examine, and third, the optional |
| 1498 | <a href="#description">additional extra text</a> to emit when the |
| 1499 | <tt>--help</tt> option is invoked.</p> |
| 1500 | |
| 1501 | <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment |
| 1502 | variable's value up into words and then process them using |
| 1503 | <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>. |
| 1504 | <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support |
| 1505 | quoting, so an environment variable containing <tt>-option "foo bar"</tt> will |
| 1506 | be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>, |
| 1507 | which is different from what you would get from the shell with the same |
| 1508 | input.</p> |
| 1509 | |
| 1510 | </div> |
| 1511 | |
| 1512 | <!-- _______________________________________________________________________ --> |
| 1513 | <div class="doc_subsubsection"> |
| 1514 | <a name="cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt> |
| 1515 | function</a> |
| 1516 | </div> |
| 1517 | |
| 1518 | <div class="doc_text"> |
| 1519 | |
| 1520 | <p>The <tt>cl::SetVersionPrinter</tt> function is designed to be called |
| 1521 | directly from <tt>main</tt>, and <i>before</i> |
| 1522 | <tt>cl::ParseCommandLineOptions</tt>. Its use is optional. It simply arranges |
| 1523 | for a function to be called in response to the <tt>--version</tt> option instead |
| 1524 | of having the <tt>CommandLine</tt> library print out the usual version string |
| 1525 | for LLVM. This is useful for programs that are not part of LLVM but wish to use |
| 1526 | the <tt>CommandLine</tt> facilities. Such programs should just define a small |
| 1527 | function that takes no arguments and returns <tt>void</tt> and that prints out |
| 1528 | whatever version information is appropriate for the program. Pass the address |
| 1529 | of that function to <tt>cl::SetVersionPrinter</tt> to arrange for it to be |
| 1530 | called when the <tt>--version</tt> option is given by the user.</p> |
| 1531 | |
| 1532 | </div> |
| 1533 | <!-- _______________________________________________________________________ --> |
| 1534 | <div class="doc_subsubsection"> |
| 1535 | <a name="cl::opt">The <tt>cl::opt</tt> class</a> |
| 1536 | </div> |
| 1537 | |
| 1538 | <div class="doc_text"> |
| 1539 | |
| 1540 | <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line |
| 1541 | options, and is the one used most of the time. It is a templated class which |
| 1542 | can take up to three arguments (all except for the first have default values |
| 1543 | though):</p> |
| 1544 | |
| 1545 | <div class="doc_code"><pre> |
| 1546 | <b>namespace</b> cl { |
| 1547 | <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>, |
| 1548 | <b>class</b> ParserClass = parser<DataType> > |
| 1549 | <b>class</b> opt; |
| 1550 | } |
| 1551 | </pre></div> |
| 1552 | |
| 1553 | <p>The first template argument specifies what underlying data type the command |
| 1554 | line argument is, and is used to select a default parser implementation. The |
| 1555 | second template argument is used to specify whether the option should contain |
| 1556 | the storage for the option (the default) or whether external storage should be |
| 1557 | used to contain the value parsed for the option (see <a href="#storage">Internal |
| 1558 | vs External Storage</a> for more information).</p> |
| 1559 | |
| 1560 | <p>The third template argument specifies which parser to use. The default value |
| 1561 | selects an instantiation of the <tt>parser</tt> class based on the underlying |
| 1562 | data type of the option. In general, this default works well for most |
| 1563 | applications, so this option is only used when using a <a |
| 1564 | href="#customparser">custom parser</a>.</p> |
| 1565 | |
| 1566 | </div> |
| 1567 | |
| 1568 | <!-- _______________________________________________________________________ --> |
| 1569 | <div class="doc_subsubsection"> |
| 1570 | <a name="cl::list">The <tt>cl::list</tt> class</a> |
| 1571 | </div> |
| 1572 | |
| 1573 | <div class="doc_text"> |
| 1574 | |
| 1575 | <p>The <tt>cl::list</tt> class is the class used to represent a list of command |
| 1576 | line options. It too is a templated class which can take up to three |
| 1577 | arguments:</p> |
| 1578 | |
| 1579 | <div class="doc_code"><pre> |
| 1580 | <b>namespace</b> cl { |
| 1581 | <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, |
| 1582 | <b>class</b> ParserClass = parser<DataType> > |
| 1583 | <b>class</b> list; |
| 1584 | } |
| 1585 | </pre></div> |
| 1586 | |
| 1587 | <p>This class works the exact same as the <a |
| 1588 | href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is |
| 1589 | the <b>type</b> of the external storage, not a boolean value. For this class, |
| 1590 | the marker type '<tt>bool</tt>' is used to indicate that internal storage should |
| 1591 | be used.</p> |
| 1592 | |
| 1593 | </div> |
| 1594 | |
| 1595 | <!-- _______________________________________________________________________ --> |
| 1596 | <div class="doc_subsubsection"> |
| 1597 | <a name="cl::bits">The <tt>cl::bits</tt> class</a> |
| 1598 | </div> |
| 1599 | |
| 1600 | <div class="doc_text"> |
| 1601 | |
| 1602 | <p>The <tt>cl::bits</tt> class is the class used to represent a list of command |
| 1603 | line options in the form of a bit vector. It is also a templated class which |
| 1604 | can take up to three arguments:</p> |
| 1605 | |
| 1606 | <div class="doc_code"><pre> |
| 1607 | <b>namespace</b> cl { |
| 1608 | <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, |
| 1609 | <b>class</b> ParserClass = parser<DataType> > |
| 1610 | <b>class</b> bits; |
| 1611 | } |
| 1612 | </pre></div> |
| 1613 | |
| 1614 | <p>This class works the exact same as the <a |
| 1615 | href="#cl::opt"><tt>cl::lists</tt></a> class, except that the second argument |
| 1616 | must be of <b>type</b> <tt>unsigned</tt> if external storage is used.</p> |
| 1617 | |
| 1618 | </div> |
| 1619 | |
| 1620 | <!-- _______________________________________________________________________ --> |
| 1621 | <div class="doc_subsubsection"> |
| 1622 | <a name="cl::alias">The <tt>cl::alias</tt> class</a> |
| 1623 | </div> |
| 1624 | |
| 1625 | <div class="doc_text"> |
| 1626 | |
| 1627 | <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form |
| 1628 | aliases for other arguments.</p> |
| 1629 | |
| 1630 | <div class="doc_code"><pre> |
| 1631 | <b>namespace</b> cl { |
| 1632 | <b>class</b> alias; |
| 1633 | } |
| 1634 | </pre></div> |
| 1635 | |
| 1636 | <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be |
| 1637 | used to specify which option this is an alias for. Alias arguments default to |
| 1638 | being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do |
| 1639 | the conversion from string to data.</p> |
| 1640 | |
| 1641 | </div> |
| 1642 | |
| 1643 | <!-- _______________________________________________________________________ --> |
| 1644 | <div class="doc_subsubsection"> |
| 1645 | <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a> |
| 1646 | </div> |
| 1647 | |
| 1648 | <div class="doc_text"> |
| 1649 | |
| 1650 | <p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra |
| 1651 | help text to be printed out for the <tt>--help</tt> option.</p> |
| 1652 | |
| 1653 | <div class="doc_code"><pre> |
| 1654 | <b>namespace</b> cl { |
| 1655 | <b>struct</b> extrahelp; |
| 1656 | } |
| 1657 | </pre></div> |
| 1658 | |
| 1659 | <p>To use the extrahelp, simply construct one with a <tt>const char*</tt> |
| 1660 | parameter to the constructor. The text passed to the constructor will be printed |
| 1661 | at the bottom of the help message, verbatim. Note that multiple |
| 1662 | <tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If |
| 1663 | your tool needs to print additional help information, put all that help into a |
| 1664 | single <tt>cl::extrahelp</tt> instance.</p> |
| 1665 | <p>For example:</p> |
| 1666 | <div class="doc_code"><pre> |
| 1667 | cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); |
| 1668 | </pre></div> |
| 1669 | </div> |
| 1670 | |
| 1671 | <!-- ======================================================================= --> |
| 1672 | <div class="doc_subsection"> |
| 1673 | <a name="builtinparsers">Builtin parsers</a> |
| 1674 | </div> |
| 1675 | |
| 1676 | <div class="doc_text"> |
| 1677 | |
| 1678 | <p>Parsers control how the string value taken from the command line is |
| 1679 | translated into a typed value, suitable for use in a C++ program. By default, |
| 1680 | the CommandLine library uses an instance of <tt>parser<type></tt> if the |
| 1681 | command line option specifies that it uses values of type '<tt>type</tt>'. |
| 1682 | Because of this, custom option processing is specified with specializations of |
| 1683 | the '<tt>parser</tt>' class.</p> |
| 1684 | |
| 1685 | <p>The CommandLine library provides the following builtin parser |
| 1686 | specializations, which are sufficient for most applications. It can, however, |
| 1687 | also be extended to work with new data types and new ways of interpreting the |
| 1688 | same data. See the <a href="#customparser">Writing a Custom Parser</a> for more |
| 1689 | details on this type of library extension.</p> |
| 1690 | |
| 1691 | <ul> |
| 1692 | |
| 1693 | <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a> |
| 1694 | can be used to map strings values to any data type, through the use of the <a |
| 1695 | href="#cl::values">cl::values</a> property, which specifies the mapping |
| 1696 | information. The most common use of this parser is for parsing enum values, |
| 1697 | which allows you to use the CommandLine library for all of the error checking to |
| 1698 | make sure that only valid enum values are specified (as opposed to accepting |
| 1699 | arbitrary strings). Despite this, however, the generic parser class can be used |
| 1700 | for any data type.</li> |
| 1701 | |
| 1702 | <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a> |
| 1703 | is used to convert boolean strings to a boolean value. Currently accepted |
| 1704 | strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>", |
| 1705 | "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li> |
| 1706 | |
| 1707 | <li><a name="boolOrDefaultparser">The <b><tt>parser<boolOrDefault></tt> |
| 1708 | specialization</b></a> is used for cases where the value is boolean, |
| 1709 | but we also need to know whether the option was specified at all. boolOrDefault |
| 1710 | is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. This parser accepts |
| 1711 | the same strings as <b><tt>parser<bool></tt></b>.</li> |
| 1712 | |
| 1713 | <li><a name="stringparser">The <b><tt>parser<string></tt> |
| 1714 | specialization</b></a> simply stores the parsed string into the string value |
| 1715 | specified. No conversion or modification of the data is performed.</li> |
| 1716 | |
| 1717 | <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a> |
| 1718 | uses the C <tt>strtol</tt> function to parse the string input. As such, it will |
| 1719 | accept a decimal number (with an optional '+' or '-' prefix) which must start |
| 1720 | with a non-zero digit. It accepts octal numbers, which are identified with a |
| 1721 | '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of |
| 1722 | '<tt>0x</tt>' or '<tt>0X</tt>'.</li> |
| 1723 | |
| 1724 | <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and |
| 1725 | <b><tt>parser<float></tt> specializations</b> use the standard C |
| 1726 | <tt>strtod</tt> function to convert floating point strings into floating point |
| 1727 | values. As such, a broad range of string formats is supported, including |
| 1728 | exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales. |
| 1729 | </li> |
| 1730 | |
| 1731 | </ul> |
| 1732 | |
| 1733 | </div> |
| 1734 | |
| 1735 | <!-- *********************************************************************** --> |
| 1736 | <div class="doc_section"> |
| 1737 | <a name="extensionguide">Extension Guide</a> |
| 1738 | </div> |
| 1739 | <!-- *********************************************************************** --> |
| 1740 | |
| 1741 | <div class="doc_text"> |
| 1742 | |
| 1743 | <p>Although the CommandLine library has a lot of functionality built into it |
| 1744 | already (as discussed previously), one of its true strengths lie in its |
| 1745 | extensibility. This section discusses how the CommandLine library works under |
| 1746 | the covers and illustrates how to do some simple, common, extensions.</p> |
| 1747 | |
| 1748 | </div> |
| 1749 | |
| 1750 | <!-- ======================================================================= --> |
| 1751 | <div class="doc_subsection"> |
| 1752 | <a name="customparser">Writing a custom parser</a> |
| 1753 | </div> |
| 1754 | |
| 1755 | <div class="doc_text"> |
| 1756 | |
| 1757 | <p>One of the simplest and most common extensions is the use of a custom parser. |
| 1758 | As <a href="#builtinparsers">discussed previously</a>, parsers are the portion |
| 1759 | of the CommandLine library that turns string input from the user into a |
| 1760 | particular parsed data type, validating the input in the process.</p> |
| 1761 | |
| 1762 | <p>There are two ways to use a new parser:</p> |
| 1763 | |
| 1764 | <ol> |
| 1765 | |
| 1766 | <li> |
| 1767 | |
| 1768 | <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for |
| 1769 | your custom data type.<p> |
| 1770 | |
| 1771 | <p>This approach has the advantage that users of your custom data type will |
| 1772 | automatically use your custom parser whenever they define an option with a value |
| 1773 | type of your data type. The disadvantage of this approach is that it doesn't |
| 1774 | work if your fundamental data type is something that is already supported.</p> |
| 1775 | |
| 1776 | </li> |
| 1777 | |
| 1778 | <li> |
| 1779 | |
| 1780 | <p>Write an independent class, using it explicitly from options that need |
| 1781 | it.</p> |
| 1782 | |
| 1783 | <p>This approach works well in situations where you would line to parse an |
| 1784 | option using special syntax for a not-very-special data-type. The drawback of |
| 1785 | this approach is that users of your parser have to be aware that they are using |
| 1786 | your parser, instead of the builtin ones.</p> |
| 1787 | |
| 1788 | </li> |
| 1789 | |
| 1790 | </ol> |
| 1791 | |
| 1792 | <p>To guide the discussion, we will discuss a custom parser that accepts file |
| 1793 | sizes, specified with an optional unit after the numeric size. For example, we |
| 1794 | would like to parse "102kb", "41M", "1G" into the appropriate integer value. In |
| 1795 | this case, the underlying data type we want to parse into is |
| 1796 | '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make |
| 1797 | this the default for all <tt>unsigned</tt> options.</p> |
| 1798 | |
| 1799 | <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p> |
| 1800 | |
| 1801 | <div class="doc_code"><pre> |
| 1802 | <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> { |
| 1803 | <i>// parse - Return true on error.</i> |
| 1804 | <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue, |
| 1805 | <b>unsigned</b> &Val); |
| 1806 | }; |
| 1807 | </pre></div> |
| 1808 | |
| 1809 | <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to |
| 1810 | fill in the default, boiler plate, code for us. We give it the data type that |
| 1811 | we parse into (the last argument to the <tt>parse</tt> method so that clients of |
| 1812 | our custom parser know what object type to pass in to the parse method (here we |
| 1813 | declare that we parse into '<tt>unsigned</tt>' variables.</p> |
| 1814 | |
| 1815 | <p>For most purposes, the only method that must be implemented in a custom |
| 1816 | parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called |
| 1817 | whenever the option is invoked, passing in the option itself, the option name, |
| 1818 | the string to parse, and a reference to a return value. If the string to parse |
| 1819 | is not well formed, the parser should output an error message and return true. |
| 1820 | Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In |
| 1821 | our example, we implement <tt>parse</tt> as:</p> |
| 1822 | |
| 1823 | <div class="doc_code"><pre> |
| 1824 | <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName, |
| 1825 | <b>const</b> std::string &Arg, <b>unsigned</b> &Val) { |
| 1826 | <b>const char</b> *ArgStart = Arg.c_str(); |
| 1827 | <b>char</b> *End; |
| 1828 | |
| 1829 | <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i> |
| 1830 | Val = (unsigned)strtol(ArgStart, &End, 0); |
| 1831 | |
| 1832 | <b>while</b> (1) { |
| 1833 | <b>switch</b> (*End++) { |
| 1834 | <b>case</b> 0: <b>return</b> false; <i>// No error</i> |
| 1835 | <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i> |
| 1836 | <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i> |
| 1837 | <b>break</b>; |
| 1838 | |
| 1839 | <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>; |
| 1840 | <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>; |
| 1841 | <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>; |
| 1842 | |
| 1843 | default: |
| 1844 | <i>// Print an error message if unrecognized character!</i> |
| 1845 | <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!"); |
| 1846 | } |
| 1847 | } |
| 1848 | } |
| 1849 | </pre></div> |
| 1850 | |
| 1851 | <p>This function implements a very simple parser for the kinds of strings we are |
| 1852 | interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for |
| 1853 | example), it is good enough for this example. Note that we use the option |
| 1854 | itself to print out the error message (the <tt>error</tt> method always returns |
| 1855 | true) in order to get a nice error message (shown below). Now that we have our |
| 1856 | parser class, we can use it like this:</p> |
| 1857 | |
| 1858 | <div class="doc_code"><pre> |
| 1859 | <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser> |
| 1860 | MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>), |
| 1861 | <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>")); |
| 1862 | </pre></div> |
| 1863 | |
| 1864 | <p>Which adds this to the output of our program:</p> |
| 1865 | |
| 1866 | <div class="doc_code"><pre> |
| 1867 | OPTIONS: |
| 1868 | -help - display available options (--help-hidden for more) |
| 1869 | ... |
| 1870 | <b>-max-file-size=<size> - Maximum file size to accept</b> |
| 1871 | </pre></div> |
| 1872 | |
| 1873 | <p>And we can test that our parse works correctly now (the test program just |
| 1874 | prints out the max-file-size argument value):</p> |
| 1875 | |
| 1876 | <div class="doc_code"><pre> |
| 1877 | $ ./test |
| 1878 | MFS: 0 |
| 1879 | $ ./test -max-file-size=123MB |
| 1880 | MFS: 128974848 |
| 1881 | $ ./test -max-file-size=3G |
| 1882 | MFS: 3221225472 |
| 1883 | $ ./test -max-file-size=dog |
| 1884 | -max-file-size option: 'dog' value invalid for file size argument! |
| 1885 | </pre></div> |
| 1886 | |
| 1887 | <p>It looks like it works. The error message that we get is nice and helpful, |
| 1888 | and we seem to accept reasonable file sizes. This wraps up the "custom parser" |
| 1889 | tutorial.</p> |
| 1890 | |
| 1891 | </div> |
| 1892 | |
| 1893 | <!-- ======================================================================= --> |
| 1894 | <div class="doc_subsection"> |
| 1895 | <a name="explotingexternal">Exploiting external storage</a> |
| 1896 | </div> |
| 1897 | |
| 1898 | <div class="doc_text"> |
| 1899 | <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that |
| 1900 | will automatically be included in any program that links with that library. |
| 1901 | This is a feature. However, sometimes it is necessary to know the value of the |
| 1902 | command line option outside of the library. In these cases the library does or |
| 1903 | should provide an external storage location that is accessible to users of the |
| 1904 | library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the |
| 1905 | <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt> |
| 1906 | flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p> |
| 1907 | |
| 1908 | <p>TODO: complete this section</p> |
| 1909 | |
| 1910 | </div> |
| 1911 | |
| 1912 | <!-- ======================================================================= --> |
| 1913 | <div class="doc_subsection"> |
| 1914 | <a name="dynamicopts">Dynamically adding command line options</a> |
| 1915 | </div> |
| 1916 | |
| 1917 | <div class="doc_text"> |
| 1918 | |
| 1919 | <p>TODO: fill in this section</p> |
| 1920 | |
| 1921 | </div> |
| 1922 | |
| 1923 | <!-- *********************************************************************** --> |
| 1924 | |
| 1925 | <hr> |
| 1926 | <address> |
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| 1931 | |
| 1932 | <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> |
| 1933 | <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br> |
| 1934 | Last modified: $Date$ |
| 1935 | </address> |
| 1936 | |
| 1937 | </body> |
| 1938 | </html> |