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12 CommandLine 2.0 Library Manual
16 <li><a href="#introduction">Introduction</a></li>
18 <li><a href="#quickstart">Quick Start Guide</a>
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>
30 <li><a href="#referenceguide">Reference Guide</a>
32 <li><a href="#positional">Positional Arguments</a>
34 <li><a href="#--">Specifying positional options with hyphens</a></li>
35 <li><a href="#getPosition">Determining absolute position with
37 <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
41 <li><a href="#storage">Internal vs External Storage</a></li>
43 <li><a href="#attributes">Option Attributes</a></li>
45 <li><a href="#modifiers">Option Modifiers</a>
47 <li><a href="#hiding">Hiding an option from <tt>--help</tt>
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
53 <li><a href="#formatting">Controlling other formatting options</a></li>
54 <li><a href="#misc">Miscellaneous option modifiers</a></li>
57 <li><a href="#toplevel">Top-Level Classes and Functions</a>
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::opt">The <tt>cl::opt</tt> class</a></li>
64 <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li>
65 <li><a href="#cl::bits">The <tt>cl::bits</tt> class</a></li>
66 <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li>
67 <li><a href="#cl::extrahelp">The <tt>cl::extrahelp</tt> class</a></li>
70 <li><a href="#builtinparsers">Builtin parsers</a>
72 <li><a href="#genericparser">The Generic <tt>parser<t></tt>
74 <li><a href="#boolparser">The <tt>parser<bool></tt>
75 specialization</a></li>
76 <li><a href="#stringparser">The <tt>parser<string></tt>
77 specialization</a></li>
78 <li><a href="#intparser">The <tt>parser<int></tt>
79 specialization</a></li>
80 <li><a href="#doubleparser">The <tt>parser<double></tt> and
81 <tt>parser<float></tt> specializations</a></li>
84 <li><a href="#extensionguide">Extension Guide</a>
86 <li><a href="#customparser">Writing a custom parser</a></li>
87 <li><a href="#explotingexternal">Exploiting external storage</a></li>
88 <li><a href="#dynamicopts">Dynamically adding command line
93 <div class="doc_author">
94 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
97 <!-- *********************************************************************** -->
98 <div class="doc_section">
99 <a name="introduction">Introduction</a>
101 <!-- *********************************************************************** -->
103 <div class="doc_text">
105 <p>This document describes the CommandLine argument processing library. It will
106 show you how to use it, and what it can do. The CommandLine library uses a
107 declarative approach to specifying the command line options that your program
108 takes. By default, these options declarations implicitly hold the value parsed
109 for the option declared (of course this <a href="#storage">can be
112 <p>Although there are a <b>lot</b> of command line argument parsing libraries
113 out there in many different languages, none of them fit well with what I needed.
114 By looking at the features and problems of other libraries, I designed the
115 CommandLine library to have the following features:</p>
118 <li>Speed: The CommandLine library is very quick and uses little resources. The
119 parsing time of the library is directly proportional to the number of arguments
120 parsed, not the the number of options recognized. Additionally, command line
121 argument values are captured transparently into user defined global variables,
122 which can be accessed like any other variable (and with the same
125 <li>Type Safe: As a user of CommandLine, you don't have to worry about
126 remembering the type of arguments that you want (is it an int? a string? a
127 bool? an enum?) and keep casting it around. Not only does this help prevent
128 error prone constructs, it also leads to dramatically cleaner source code.</li>
130 <li>No subclasses required: To use CommandLine, you instantiate variables that
131 correspond to the arguments that you would like to capture, you don't subclass a
132 parser. This means that you don't have to write <b>any</b> boilerplate
135 <li>Globally accessible: Libraries can specify command line arguments that are
136 automatically enabled in any tool that links to the library. This is possible
137 because the application doesn't have to keep a "list" of arguments to pass to
138 the parser. This also makes supporting <a href="#dynamicopts">dynamically
139 loaded options</a> trivial.</li>
141 <li>Cleaner: CommandLine supports enum and other types directly, meaning that
142 there is less error and more security built into the library. You don't have to
143 worry about whether your integral command line argument accidentally got
144 assigned a value that is not valid for your enum type.</li>
146 <li>Powerful: The CommandLine library supports many different types of
147 arguments, from simple <a href="#boolparser">boolean flags</a> to <a
148 href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
149 href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
150 href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
151 arguments</a>. This is possible because CommandLine is...</li>
153 <li>Extensible: It is very simple to add a new argument type to CommandLine.
154 Simply specify the parser that you want to use with the command line option when
155 you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li>
157 <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
158 that you, the user, have to do. For example, it automatically provides a
159 <tt>--help</tt> option that shows the available command line options for your
160 tool. Additionally, it does most of the basic correctness checking for
163 <li>Capable: The CommandLine library can handle lots of different forms of
164 options often found in real programs. For example, <a
165 href="#positional">positional</a> arguments, <tt>ls</tt> style <a
166 href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
167 -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
168 options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
169 href="#cl::ConsumeAfter">interpreter style options</a>.</li>
173 <p>This document will hopefully let you jump in and start using CommandLine in
174 your utility quickly and painlessly. Additionally it should be a simple
175 reference manual to figure out how stuff works. If it is failing in some area
176 (or you want an extension to the library), nag the author, <a
177 href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
181 <!-- *********************************************************************** -->
182 <div class="doc_section">
183 <a name="quickstart">Quick Start Guide</a>
185 <!-- *********************************************************************** -->
187 <div class="doc_text">
189 <p>This section of the manual runs through a simple CommandLine'ification of a
190 basic compiler tool. This is intended to show you how to jump into using the
191 CommandLine library in your own program, and show you some of the cool things it
194 <p>To start out, you need to include the CommandLine header file into your
197 <div class="doc_code"><pre>
198 #include "llvm/Support/CommandLine.h"
201 <p>Additionally, you need to add this as the first line of your main
204 <div class="doc_code"><pre>
205 int main(int argc, char **argv) {
206 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
211 <p>... which actually parses the arguments and fills in the variable
214 <p>Now that you are ready to support command line arguments, we need to tell the
215 system which ones we want, and what type of argument they are. The CommandLine
216 library uses a declarative syntax to model command line arguments with the
217 global variable declarations that capture the parsed values. This means that
218 for every command line option that you would like to support, there should be a
219 global variable declaration to capture the result. For example, in a compiler,
220 we would like to support the unix standard '<tt>-o <filename></tt>' option
221 to specify where to put the output. With the CommandLine library, this is
222 represented like this:</p>
224 <a name="value_desc_example"></a>
225 <div class="doc_code"><pre>
226 <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>"));
229 <p>This declares a global variable "<tt>OutputFilename</tt>" that is used to
230 capture the result of the "<tt>o</tt>" argument (first parameter). We specify
231 that this is a simple scalar option by using the "<tt><a
232 href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a
233 href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library
234 that the data type that we are parsing is a string.</p>
236 <p>The second and third parameters (which are optional) are used to specify what
237 to output for the "<tt>--help</tt>" option. In this case, we get a line that
240 <div class="doc_code"><pre>
241 USAGE: compiler [options]
244 -help - display available options (--help-hidden for more)
245 <b>-o <filename> - Specify output filename</b>
248 <p>Because we specified that the command line option should parse using the
249 <tt>string</tt> data type, the variable declared is automatically usable as a
250 real string in all contexts that a normal C++ string object may be used. For
253 <div class="doc_code"><pre>
255 ofstream Output(OutputFilename.c_str());
260 <p>There are many different options that you can use to customize the command
261 line option handling library, but the above example shows the general interface
262 to these options. The options can be specified in any order, and are specified
263 with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
264 there are no positional dependencies to remember. The available options are
265 discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p>
267 <p>Continuing the example, we would like to have our compiler take an input
268 filename as well as an output filename, but we do not want the input filename to
269 be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
270 style of argument, the CommandLine library allows for <a
271 href="#positional">positional</a> arguments to be specified for the program.
272 These positional arguments are filled with command line parameters that are not
273 in option form. We use this feature like this:</p>
275 <div class="doc_code"><pre>
276 <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>"));
279 <p>This declaration indicates that the first positional argument should be
280 treated as the input filename. Here we use the <tt><a
281 href="#cl::init">cl::init</a></tt> option to specify an initial value for the
282 command line option, which is used if the option is not specified (if you do not
283 specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
284 the default constructor for the data type is used to initialize the value).
285 Command line options default to being optional, so if we would like to require
286 that the user always specify an input filename, we would add the <tt><a
287 href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
288 <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p>
290 <div class="doc_code"><pre>
291 <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>);
294 <p>Again, the CommandLine library does not require the options to be specified
295 in any particular order, so the above declaration is equivalent to:</p>
297 <div class="doc_code"><pre>
298 <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>"));
301 <p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag,
302 the CommandLine library will automatically issue an error if the argument is not
303 specified, which shifts all of the command line option verification code out of
304 your application into the library. This is just one example of how using flags
305 can alter the default behaviour of the library, on a per-option basis. By
306 adding one of the declarations above, the <tt>--help</tt> option synopsis is now
309 <div class="doc_code"><pre>
310 USAGE: compiler [options] <b><input file></b>
313 -help - display available options (--help-hidden for more)
314 -o <filename> - Specify output filename
317 <p>... indicating that an input filename is expected.</p>
321 <!-- ======================================================================= -->
322 <div class="doc_subsection">
323 <a name="bool">Boolean Arguments</a>
326 <div class="doc_text">
328 <p>In addition to input and output filenames, we would like the compiler example
329 to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
330 file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
331 compatibility with some of our users. We can support these by declaring options
332 of boolean type like this:</p>
334 <div class="doc_code"><pre>
335 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
336 <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>"));
337 <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>);
340 <p>This does what you would expect: it declares three boolean variables
341 ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
342 options. Note that the "<tt>-q</tt>" option is specified with the "<a
343 href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
344 from being shown by the standard "<tt>--help</tt>" output (note that it is still
345 shown in the "<tt>--help-hidden</tt>" output).</p>
347 <p>The CommandLine library uses a <a href="#builtinparsers">different parser</a>
348 for different data types. For example, in the string case, the argument passed
349 to the option is copied literally into the content of the string variable... we
350 obviously cannot do that in the boolean case, however, so we must use a smarter
351 parser. In the case of the boolean parser, it allows no options (in which case
352 it assigns the value of true to the variable), or it allows the values
353 "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
354 following inputs:</p>
356 <div class="doc_code"><pre>
357 compiler -f # No value, 'Force' == true
358 compiler -f=true # Value specified, 'Force' == true
359 compiler -f=TRUE # Value specified, 'Force' == true
360 compiler -f=FALSE # Value specified, 'Force' == false
363 <p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns
364 the string values into boolean values, and rejects things like '<tt>compiler
365 -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
366 href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
367 like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
368 library calls to parse the string value into the specified data type.</p>
370 <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
372 <div class="doc_code"><pre>
373 USAGE: compiler [options] <input file>
376 <b>-f - Overwrite output files</b>
377 -o - Override output filename
378 <b>-quiet - Don't print informational messages</b>
379 -help - display available options (--help-hidden for more)
382 <p>and "<tt>opt --help-hidden</tt>" prints this:</p>
384 <div class="doc_code"><pre>
385 USAGE: compiler [options] <input file>
388 -f - Overwrite output files
389 -o - Override output filename
390 <b>-q - Don't print informational messages</b>
391 -quiet - Don't print informational messages
392 -help - display available options (--help-hidden for more)
395 <p>This brief example has shown you how to use the '<tt><a
396 href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
397 arguments. In addition to simple scalar arguments, the CommandLine library also
398 provides primitives to support CommandLine option <a href="#alias">aliases</a>,
399 and <a href="#list">lists</a> of options.</p>
403 <!-- ======================================================================= -->
404 <div class="doc_subsection">
405 <a name="alias">Argument Aliases</a>
408 <div class="doc_text">
410 <p>So far, the example works well, except for the fact that we need to check the
411 quiet condition like this now:</p>
413 <div class="doc_code"><pre>
415 if (!Quiet && !Quiet2) printInformationalMessage(...);
419 <p>... which is a real pain! Instead of defining two values for the same
420 condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
421 option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
424 <div class="doc_code"><pre>
425 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
426 <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>"));
427 <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));
430 <p>The third line (which is the only one we modified from above) defines a
431 "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by
432 the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
433 specified. Because aliases do not hold state, the only thing the program has to
434 query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
435 that they automatically hide themselves from the <tt>-help</tt> output
436 (although, again, they are still visible in the <tt>--help-hidden
439 <p>Now the application code can simply use:</p>
441 <div class="doc_code"><pre>
443 if (!Quiet) printInformationalMessage(...);
447 <p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>"
448 can be used to specify an alternative name for any variable type, and has many
453 <!-- ======================================================================= -->
454 <div class="doc_subsection">
455 <a name="onealternative">Selecting an alternative from a set of
459 <div class="doc_text">
461 <p>So far, we have seen how the CommandLine library handles builtin types like
462 <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
463 things it doesn't know about, like enums or '<tt>int*</tt>'s?</p>
465 <p>The answer is that it uses a table driven generic parser (unless you specify
466 your own parser, as described in the <a href="#extensionguide">Extension
467 Guide</a>). This parser maps literal strings to whatever type is required, and
468 requires you to tell it what this mapping should be.</p>
470 <p>Lets say that we would like to add four optimization levels to our
471 optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>",
472 "<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean
473 options like above, but there are several problems with this strategy:</p>
476 <li>A user could specify more than one of the options at a time, for example,
477 "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this
478 erroneous input for us.</li>
480 <li>We would have to test 4 different variables to see which ones are set.</li>
482 <li>This doesn't map to the numeric levels that we want... so we cannot easily
483 see if some level >= "<tt>-O1</tt>" is enabled.</li>
487 <p>To cope with these problems, we can use an enum value, and have the
488 CommandLine library fill it in with the appropriate level directly, which is
491 <div class="doc_code"><pre>
496 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
497 <a href="#cl::values">cl::values</a>(
498 clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
499 clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
500 clEnumVal(O2, "<i>Enable default optimizations</i>"),
501 clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
505 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
509 <p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
510 "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
511 that are listed in the declaration (Note that the declaration list must be
512 terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine
514 that the user can only specify one of the options, and it ensure that only valid
515 enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
516 command line arguments matched the enum values. With this option added, our
517 help output now is:</p>
519 <div class="doc_code"><pre>
520 USAGE: compiler [options] <input file>
523 <b>Choose optimization level:
524 -g - No optimizations, enable debugging
525 -O1 - Enable trivial optimizations
526 -O2 - Enable default optimizations
527 -O3 - Enable expensive optimizations</b>
528 -f - Overwrite output files
529 -help - display available options (--help-hidden for more)
530 -o <filename> - Specify output filename
531 -quiet - Don't print informational messages
534 <p>In this case, it is sort of awkward that flag names correspond directly to
535 enum names, because we probably don't want a enum definition named "<tt>g</tt>"
536 in our program. Because of this, we can alternatively write this example like
539 <div class="doc_code"><pre>
544 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
545 <a href="#cl::values">cl::values</a>(
546 clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
547 clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
548 clEnumVal(O2 , "<i>Enable default optimizations</i>"),
549 clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
553 if (OptimizationLevel == Debug) outputDebugInfo(...);
557 <p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we
558 can directly specify the name that the flag should get. In general a direct
559 mapping is nice, but sometimes you can't or don't want to preserve the mapping,
560 which is when you would use it.</p>
564 <!-- ======================================================================= -->
565 <div class="doc_subsection">
566 <a name="namedalternatives">Named Alternatives</a>
569 <div class="doc_text">
571 <p>Another useful argument form is a named alternative style. We shall use this
572 style in our compiler to specify different debug levels that can be used.
573 Instead of each debug level being its own switch, we want to support the
574 following options, of which only one can be specified at a time:
575 "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
576 "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
577 our optimization level flags, but we also specify an option name. For this
578 case, the code looks like this:</p>
580 <div class="doc_code"><pre>
582 nodebuginfo, quick, detailed
585 // Enable Debug Options to be specified on the command line
586 <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>"),
587 <a href="#cl::values">cl::values</a>(
588 clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
589 clEnumVal(quick, "<i>enable quick debug information</i>"),
590 clEnumVal(detailed, "<i>enable detailed debug information</i>"),
594 <p>This definition defines an enumerated command line variable of type "<tt>enum
595 DebugLev</tt>", which works exactly the same way as before. The difference here
596 is just the interface exposed to the user of your program and the help output by
597 the "<tt>--help</tt>" option:</p>
599 <div class="doc_code"><pre>
600 USAGE: compiler [options] <input file>
603 Choose optimization level:
604 -g - No optimizations, enable debugging
605 -O1 - Enable trivial optimizations
606 -O2 - Enable default optimizations
607 -O3 - Enable expensive optimizations
608 <b>-debug_level - Set the debugging level:
609 =none - disable debug information
610 =quick - enable quick debug information
611 =detailed - enable detailed debug information</b>
612 -f - Overwrite output files
613 -help - display available options (--help-hidden for more)
614 -o <filename> - Specify output filename
615 -quiet - Don't print informational messages
618 <p>Again, the only structural difference between the debug level declaration and
619 the optimization level declaration is that the debug level declaration includes
620 an option name (<tt>"debug_level"</tt>), which automatically changes how the
621 library processes the argument. The CommandLine library supports both forms so
622 that you can choose the form most appropriate for your application.</p>
626 <!-- ======================================================================= -->
627 <div class="doc_subsection">
628 <a name="list">Parsing a list of options</a>
631 <div class="doc_text">
633 <p>Now that we have the standard run of the mill argument types out of the way,
634 lets get a little wild and crazy. Lets say that we want our optimizer to accept
635 a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
636 might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
637 this case, the order of the arguments and the number of appearances is very
638 important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
639 template is for. First, start by defining an enum of the optimizations that you
640 would like to perform:</p>
642 <div class="doc_code"><pre>
644 // 'inline' is a C++ keyword, so name it 'inlining'
645 dce, constprop, inlining, strip
649 <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
651 <div class="doc_code"><pre>
652 <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
653 <a href="#cl::values">cl::values</a>(
654 clEnumVal(dce , "<i>Dead Code Elimination</i>"),
655 clEnumVal(constprop , "<i>Constant Propagation</i>"),
656 clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
657 clEnumVal(strip , "<i>Strip Symbols</i>"),
661 <p>This defines a variable that is conceptually of the type
662 "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
665 <div class="doc_code"><pre>
666 for (unsigned i = 0; i != OptimizationList.size(); ++i)
667 switch (OptimizationList[i])
671 <p>... to iterate through the list of options specified.</p>
673 <p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is
674 completely general and may be used with any data types or other arguments that
675 you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One
676 especially useful way to use a list is to capture all of the positional
677 arguments together if there may be more than one specified. In the case of a
678 linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to
679 capture them into a list. This is naturally specified as:</p>
681 <div class="doc_code"><pre>
683 <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>);
687 <p>This variable works just like a "<tt>vector<string></tt>" object. As
688 such, accessing the list is simple, just like above. In this example, we used
689 the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
690 CommandLine library that it is an error if the user does not specify any
691 <tt>.o</tt> files on our command line. Again, this just reduces the amount of
692 checking we have to do.</p>
696 <!-- ======================================================================= -->
697 <div class="doc_subsection">
698 <a name="bits">Collecting options as a set of flags</a>
701 <div class="doc_text">
703 <p>Instead of collecting sets of options in a list, it is also possible to
704 gather information for enum values in a <b>bit vector</b>. The represention used by
705 the <a href="#bits"><tt>cl::bits</tt></a> class is an <tt>unsigned</tt>
706 integer. An enum value is represented by a 0/1 in the enum's ordinal value bit
707 position. 1 indicating that the enum was specified, 0 otherwise. As each
708 specified value is parsed, the resulting enum's bit is set in the option's bit
711 <div class="doc_code"><pre>
712 <i>bits</i> |= 1 << (unsigned)<i>enum</i>;
715 <p>Options that are specified multiple times are redundant. Any instances after
716 the first are discarded.</p>
718 <p>Reworking the above list example, we could replace <a href="#list">
719 <tt>cl::list</tt></a> with <a href="#bits"><tt>cl::bits</tt></a>:</p>
721 <div class="doc_code"><pre>
722 <a href="#cl::bits">cl::bits</a><Opts> OptimizationBits(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
723 <a href="#cl::values">cl::values</a>(
724 clEnumVal(dce , "<i>Dead Code Elimination</i>"),
725 clEnumVal(constprop , "<i>Constant Propagation</i>"),
726 clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
727 clEnumVal(strip , "<i>Strip Symbols</i>"),
731 <p>To test to see if <tt>constprop</tt> was specified, we can use the
732 <tt>cl:bits::isSet</tt> function:</p>
734 <div class="doc_code"><pre>
735 if (OptimizationBits.isSet(constprop)) {
740 <p>It's also possible to get the raw bit vector using the
741 <tt>cl::bits::getBits</tt> function:</p>
743 <div class="doc_code"><pre>
744 unsigned bits = OptimizationBits.getBits();
747 <p>Finally, if external storage is used, then the location specified must be of
748 <b>type</b> <tt>unsigned</tt>. In all other ways a <a
749 href="#bits"><tt>cl::bits</tt></a> option is morally equivalent to a <a
750 href="#list"> <tt>cl::list</tt></a> option.</p>
755 <!-- ======================================================================= -->
756 <div class="doc_subsection">
757 <a name="description">Adding freeform text to help output</a>
760 <div class="doc_text">
762 <p>As our program grows and becomes more mature, we may decide to put summary
763 information about what it does into the help output. The help output is styled
764 to look similar to a Unix <tt>man</tt> page, providing concise information about
765 a program. Unix <tt>man</tt> pages, however often have a description about what
766 the program does. To add this to your CommandLine program, simply pass a third
768 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
769 call in main. This additional argument is then printed as the overview
770 information for your program, allowing you to include any additional information
771 that you want. For example:</p>
773 <div class="doc_code"><pre>
774 int main(int argc, char **argv) {
775 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
776 " This program blah blah blah...\n");
781 <p>would yield the help output:</p>
783 <div class="doc_code"><pre>
784 <b>OVERVIEW: CommandLine compiler example
786 This program blah blah blah...</b>
788 USAGE: compiler [options] <input file>
792 -help - display available options (--help-hidden for more)
793 -o <filename> - Specify output filename
799 <!-- *********************************************************************** -->
800 <div class="doc_section">
801 <a name="referenceguide">Reference Guide</a>
803 <!-- *********************************************************************** -->
805 <div class="doc_text">
807 <p>Now that you know the basics of how to use the CommandLine library, this
808 section will give you the detailed information you need to tune how command line
809 options work, as well as information on more "advanced" command line option
810 processing capabilities.</p>
814 <!-- ======================================================================= -->
815 <div class="doc_subsection">
816 <a name="positional">Positional Arguments</a>
819 <div class="doc_text">
821 <p>Positional arguments are those arguments that are not named, and are not
822 specified with a hyphen. Positional arguments should be used when an option is
823 specified by its position alone. For example, the standard Unix <tt>grep</tt>
824 tool takes a regular expression argument, and an optional filename to search
825 through (which defaults to standard input if a filename is not specified).
826 Using the CommandLine library, this would be specified as:</p>
828 <div class="doc_code"><pre>
829 <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>);
830 <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>"));
833 <p>Given these two option declarations, the <tt>--help</tt> output for our grep
834 replacement would look like this:</p>
836 <div class="doc_code"><pre>
837 USAGE: spiffygrep [options] <b><regular expression> <input file></b>
840 -help - display available options (--help-hidden for more)
843 <p>... and the resultant program could be used just like the standard
844 <tt>grep</tt> tool.</p>
846 <p>Positional arguments are sorted by their order of construction. This means
847 that command line options will be ordered according to how they are listed in a
848 .cpp file, but will not have an ordering defined if the positional arguments
849 are defined in multiple .cpp files. The fix for this problem is simply to
850 define all of your positional arguments in one .cpp file.</p>
855 <!-- _______________________________________________________________________ -->
856 <div class="doc_subsubsection">
857 <a name="--">Specifying positional options with hyphens</a>
860 <div class="doc_text">
862 <p>Sometimes you may want to specify a value to your positional argument that
863 starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
864 first, you will have trouble doing this, because it will try to find an argument
865 named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
866 Note that the system <tt>grep</tt> has the same problem:</p>
868 <div class="doc_code"><pre>
869 $ spiffygrep '-foo' test.txt
870 Unknown command line argument '-foo'. Try: spiffygrep --help'
872 $ grep '-foo' test.txt
873 grep: illegal option -- f
874 grep: illegal option -- o
875 grep: illegal option -- o
876 Usage: grep -hblcnsviw pattern file . . .
879 <p>The solution for this problem is the same for both your tool and the system
880 version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
881 the command line, it is telling the program that all options after the
882 '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
883 can use it like this:</p>
885 <div class="doc_code"><pre>
886 $ spiffygrep -- -foo test.txt
892 <!-- _______________________________________________________________________ -->
893 <div class="doc_subsubsection">
894 <a name="getPosition">Determining absolute position with getPosition()</a>
896 <div class="doc_text">
897 <p>Sometimes an option can affect or modify the meaning of another option. For
898 example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells
899 <tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force
900 the file to be interpreted as if it contained source code in language
901 <tt>LANG</tt>. In order to handle this properly , you need to know the
902 absolute position of each argument, especially those in lists, so their
903 interaction(s) can be applied correctly. This is also useful for options like
904 <tt>-llibname</tt> which is actually a positional argument that starts with
906 <p>So, generally, the problem is that you have two <tt>cl::list</tt> variables
907 that interact in some way. To ensure the correct interaction, you can use the
908 <tt>cl::list::getPosition(optnum)</tt> method. This method returns the
909 absolute position (as found on the command line) of the <tt>optnum</tt>
910 item in the <tt>cl::list</tt>.</p>
911 <p>The idiom for usage is like this:</p>
913 <div class="doc_code"><pre>
914 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
915 static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore);
917 int main(int argc, char**argv) {
919 std::vector<std::string>::iterator fileIt = Files.begin();
920 std::vector<std::string>::iterator libIt = Libraries.begin();
921 unsigned libPos = 0, filePos = 0;
923 if ( libIt != Libraries.end() )
924 libPos = Libraries.getPosition( libIt - Libraries.begin() );
927 if ( fileIt != Files.end() )
928 filePos = Files.getPosition( fileIt - Files.begin() );
932 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
933 // Source File Is next
936 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
941 break; // we're done with the list
945 <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an
946 <tt>unsigned getPosition()</tt> option that will provide the absolute position
947 of that option. You can apply the same approach as above with a
948 <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p>
951 <!-- _______________________________________________________________________ -->
952 <div class="doc_subsubsection">
953 <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
956 <div class="doc_text">
958 <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
959 used to construct programs that use "interpreter style" option processing. With
960 this style of option processing, all arguments specified after the last
961 positional argument are treated as special interpreter arguments that are not
962 interpreted by the command line argument.</p>
964 <p>As a concrete example, lets say we are developing a replacement for the
965 standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
966 you specify options to the shell itself (like <tt>-x</tt> which turns on trace
967 output), then you specify the name of the script to run, then you specify
968 arguments to the script. These arguments to the script are parsed by the bourne
969 shell command line option processor, but are not interpreted as options to the
970 shell itself. Using the CommandLine library, we would specify this as:</p>
972 <div class="doc_code"><pre>
973 <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>("-"));
974 <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>"));
975 <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
978 <p>which automatically provides the help output:</p>
980 <div class="doc_code"><pre>
981 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
984 -help - display available options (--help-hidden for more)
985 <b>-x - Enable trace output</b>
988 <p>At runtime, if we run our new shell replacement as `<tt>spiffysh -x test.sh
989 -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
990 <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
991 <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
992 were specified after the last positional argument (which is the script
995 <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
996 be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
997 per program, there must be at least one <a href="#positional">positional
998 argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
999 positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
1000 href="#cl::list">cl::list</a> option.</p>
1004 <!-- ======================================================================= -->
1005 <div class="doc_subsection">
1006 <a name="storage">Internal vs External Storage</a>
1009 <div class="doc_text">
1011 <p>By default, all command line options automatically hold the value that they
1012 parse from the command line. This is very convenient in the common case,
1013 especially when combined with the ability to define command line options in the
1014 files that use them. This is called the internal storage model.</p>
1016 <p>Sometimes, however, it is nice to separate the command line option processing
1017 code from the storage of the value parsed. For example, lets say that we have a
1018 '<tt>-debug</tt>' option that we would like to use to enable debug information
1019 across the entire body of our program. In this case, the boolean value
1020 controlling the debug code should be globally accessable (in a header file, for
1021 example) yet the command line option processing code should not be exposed to
1022 all of these clients (requiring lots of .cpp files to #include
1023 <tt>CommandLine.h</tt>).</p>
1025 <p>To do this, set up your .h file with your option, like this for example:</p>
1027 <div class="doc_code">
1029 <i>// DebugFlag.h - Get access to the '-debug' command line option
1032 // DebugFlag - This boolean is set to true if the '-debug' command line option
1033 // is specified. This should probably not be referenced directly, instead, use
1034 // the DEBUG macro below.
1036 extern bool DebugFlag;
1038 <i>// DEBUG macro - This macro should be used by code to emit debug information.
1039 // In the '-debug' option is specified on the command line, and if this is a
1040 // debug build, then the code specified as the option to the macro will be
1041 // executed. Otherwise it will not be. Example:
1043 // DEBUG(std::cerr << "Bitset contains: " << Bitset << "\n");
1045 <span class="doc_hilite">#ifdef NDEBUG
1048 #define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0)
1049 <span class="doc_hilite">#endif</span>
1053 <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
1054 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
1055 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
1056 an additial argument to our command line argument processor, and we specify
1057 where to fill in with the <a href="#cl::location">cl::location</a>
1060 <div class="doc_code">
1062 bool DebugFlag; <i>// the actual value</i>
1063 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
1064 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));
1068 <p>In the above example, we specify "<tt>true</tt>" as the second argument to
1069 the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the
1070 template should not maintain a copy of the value itself. In addition to this,
1071 we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so
1072 that <tt>DebugFlag</tt> is automatically set.</p>
1076 <!-- ======================================================================= -->
1077 <div class="doc_subsection">
1078 <a name="attributes">Option Attributes</a>
1081 <div class="doc_text">
1083 <p>This section describes the basic attributes that you can specify on
1088 <li>The option name attribute (which is required for all options, except <a
1089 href="#positional">positional options</a>) specifies what the option name is.
1090 This option is specified in simple double quotes:
1093 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
1098 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
1099 description for the option to be shown in the <tt>--help</tt> output for the
1102 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
1103 specifies a string that can be used to fine tune the <tt>--help</tt> output for
1104 a command line option. Look <a href="#value_desc_example">here</a> for an
1107 <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
1108 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
1109 not specified then the command line option value defaults to the value created
1110 by the default constructor for the type. <b>Warning</b>: If you specify both
1111 <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
1112 you must specify <b><tt>cl::location</tt></b> first, so that when the
1113 command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
1114 initial value. (You will get an error at runtime if you don't put them in
1115 the right order.)</li>
1117 <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
1118 store the value for a parsed command line option if using external storage. See
1119 the section on <a href="#storage">Internal vs External Storage</a> for more
1122 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
1123 specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is
1126 <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
1127 the string-to-value mapping to be used by the generic parser. It takes a
1128 <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
1130 specify the option name, the value mapped to, and the description shown in the
1131 <tt>--help</tt> for the tool. Because the generic parser is used most
1132 frequently with enum values, two macros are often useful:
1136 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
1137 nice simple way to specify a triplet for an enum. This macro automatically
1138 makes the option name be the same as the enum name. The first option to the
1139 macro is the enum, the second is the description for the command line
1142 <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
1143 specify macro options where the option name doesn't equal the enum name. For
1144 this macro, the first argument is the enum value, the second is the flag name,
1145 and the second is the description.</li>
1149 You will get a compile time error if you try to use cl::values with a parser
1150 that does not support it.</li>
1156 <!-- ======================================================================= -->
1157 <div class="doc_subsection">
1158 <a name="modifiers">Option Modifiers</a>
1161 <div class="doc_text">
1163 <p>Option modifiers are the flags and expressions that you pass into the
1164 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1165 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
1166 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
1167 your application well.</p>
1169 <p>These options fall into five main catagories:</p>
1172 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
1173 <li><a href="#numoccurrences">Controlling the number of occurrences
1174 required and allowed</a></li>
1175 <li><a href="#valrequired">Controlling whether or not a value must be
1177 <li><a href="#formatting">Controlling other formatting options</a></li>
1178 <li><a href="#misc">Miscellaneous option modifiers</a></li>
1181 <p>It is not possible to specify two options from the same catagory (you'll get
1182 a runtime error) to a single option, except for options in the miscellaneous
1183 catagory. The CommandLine library specifies defaults for all of these settings
1184 that are the most useful in practice and the most common, which mean that you
1185 usually shouldn't have to worry about these.</p>
1189 <!-- _______________________________________________________________________ -->
1190 <div class="doc_subsubsection">
1191 <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
1194 <div class="doc_text">
1196 <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
1197 <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
1198 appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
1199 compiled program:</p>
1203 <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
1204 (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1205 href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
1206 in both help listings.</li>
1208 <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
1209 default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
1210 the option should not appear in the <tt>--help</tt> output, but should appear in
1211 the <tt>--help-hidden</tt> output.</li>
1213 <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
1214 indicates that the option should not appear in any help output.</li>
1220 <!-- _______________________________________________________________________ -->
1221 <div class="doc_subsubsection">
1222 <a name="numoccurrences">Controlling the number of occurrences required and
1226 <div class="doc_text">
1228 <p>This group of options is used to control how many time an option is allowed
1229 (or required) to be specified on the command line of your program. Specifying a
1230 value for this setting allows the CommandLine library to do error checking for
1233 <p>The allowed values for this option group are:</p>
1237 <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
1238 is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1239 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1240 allow either zero or one occurrence of the option to be specified.</li>
1242 <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
1243 (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
1244 indicates that your program will allow the option to be specified zero or more
1247 <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
1248 indicates that the specified option must be specified exactly one time.</li>
1250 <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
1251 indicates that the option must be specified at least one time.</li>
1253 <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1254 href="#positional">Positional arguments section</a></li>
1258 <p>If an option is not specified, then the value of the option is equal to the
1259 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1260 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1261 option value is initialized with the default constructor for the data type.</p>
1263 <p>If an option is specified multiple times for an option of the <tt><a
1264 href="#cl::opt">cl::opt</a></tt> class, only the last value will be
1269 <!-- _______________________________________________________________________ -->
1270 <div class="doc_subsubsection">
1271 <a name="valrequired">Controlling whether or not a value must be specified</a>
1274 <div class="doc_text">
1276 <p>This group of options is used to control whether or not the option allows a
1277 value to be present. In the case of the CommandLine library, a value is either
1278 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1279 string (e.g. '<tt>-o a.out</tt>').</p>
1281 <p>The allowed values for this option group are:</p>
1285 <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
1286 (which is the default for <tt>bool</tt> typed options) specifies that it is
1287 acceptable to have a value, or not. A boolean argument can be enabled just by
1288 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1289 If an option is specified with this mode, it is illegal for the value to be
1290 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1291 get this behavior, you must use the <a
1292 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
1294 <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
1295 (which is the default for all other types except for <a
1296 href="#onealternative">unnamed alternatives using the generic parser</a>)
1297 specifies that a value must be provided. This mode informs the command line
1298 library that if an option is not provides with an equal sign, that the next
1299 argument provided must be the value. This allows things like '<tt>-o
1300 a.out</tt>' to work.</li>
1302 <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
1303 modifier (which is the default for <a href="#onealternative">unnamed
1304 alternatives using the generic parser</a>) indicates that it is a runtime error
1305 for the user to specify a value. This can be provided to disallow users from
1306 providing options to boolean options (like '<tt>-foo=true</tt>').</li>
1310 <p>In general, the default values for this option group work just like you would
1311 want them to. As mentioned above, you can specify the <a
1312 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1313 argument to restrict your command line parser. These options are mostly useful
1314 when <a href="#extensionguide">extending the library</a>.</p>
1318 <!-- _______________________________________________________________________ -->
1319 <div class="doc_subsubsection">
1320 <a name="formatting">Controlling other formatting options</a>
1323 <div class="doc_text">
1325 <p>The formatting option group is used to specify that the command line option
1326 has special abilities and is otherwise different from other command line
1327 arguments. As usual, you can only specify at most one of these arguments.</p>
1331 <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
1332 modifier (which is the default all options) specifies that this option is
1335 <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
1336 specifies that this is a positional argument, that does not have a command line
1337 option associated with it. See the <a href="#positional">Positional
1338 Arguments</a> section for more information.</li>
1340 <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1341 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
1343 <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
1344 that this option prefixes its value. With 'Prefix' options, the equal sign does
1345 not separate the value from the option name specified. Instead, the value is
1346 everything after the prefix, including any equal sign if present. This is useful
1347 for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a
1348 linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the
1349 '<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list)
1350 options, that have the <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b>
1351 modifier added to allow the CommandLine library to recognize them. Note that
1352 <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> options must not have the
1353 <b><tt><a href="#cl::ValueDisallowed">cl::ValueDisallowed</a></tt></b> modifier
1356 <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
1357 to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
1358 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1359 command actually enables four different options, all of which are single
1360 letters. Note that <b><tt><a href="#cl::Grouping">cl::Grouping</a></tt></b>
1361 options cannot have values.</li>
1365 <p>The CommandLine library does not restrict how you use the <b><tt><a
1366 href="#cl::Prefix">cl::Prefix</a></tt></b> or <b><tt><a
1367 href="#cl::Grouping">cl::Grouping</a></tt></b> modifiers, but it is possible to
1368 specify ambiguous argument settings. Thus, it is possible to have multiple
1369 letter options that are prefix or grouping options, and they will still work as
1372 <p>To do this, the CommandLine library uses a greedy algorithm to parse the
1373 input option into (potentially multiple) prefix and grouping options. The
1374 strategy basically looks like this:</p>
1376 <div class="doc_code"><tt>parse(string OrigInput) {</tt>
1379 <li><tt>string input = OrigInput;</tt>
1380 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1381 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1382 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1383 <li><tt>if (getOption(input).isPrefix())<br>
1384 return getOption(input).parse(input);</tt>
1385 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1386 getOption(input).parse();<br>
1387 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1388 input = OrigInput;<br>
1389 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1391 <li><tt>if (!OrigInput.empty()) error();</tt></li>
1399 <!-- _______________________________________________________________________ -->
1400 <div class="doc_subsubsection">
1401 <a name="misc">Miscellaneous option modifiers</a>
1404 <div class="doc_text">
1406 <p>The miscellaneous option modifiers are the only flags where you can specify
1407 more than one flag from the set: they are not mutually exclusive. These flags
1408 specify boolean properties that modify the option.</p>
1412 <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
1413 indicates that any commas specified for an option's value should be used to
1414 split the value up into multiple values for the option. For example, these two
1415 options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
1416 "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
1417 makes sense to be used in a case where the option is allowed to accept one or
1418 more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
1420 <li><a name="cl::PositionalEatsArgs">The
1421 <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
1422 positional arguments, and only makes sense for lists) indicates that positional
1423 argument should consume any strings after it (including strings that start with
1424 a "-") up until another recognized positional argument. For example, if you
1425 have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the
1426 string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
1427 -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
1428 "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
1432 <p>So far, these are the only two miscellaneous option modifiers.</p>
1436 <!-- ======================================================================= -->
1437 <div class="doc_subsection">
1438 <a name="toplevel">Top-Level Classes and Functions</a>
1441 <div class="doc_text">
1443 <p>Despite all of the built-in flexibility, the CommandLine option library
1444 really only consists of one function (<a
1445 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1446 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1447 href="#cl::list"><tt>cl::list</tt></a>, and <a
1448 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1449 classes in detail.</p>
1453 <!-- _______________________________________________________________________ -->
1454 <div class="doc_subsubsection">
1455 <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
1459 <div class="doc_text">
1461 <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1462 directly from <tt>main</tt>, and is used to fill in the values of all of the
1463 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1466 <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1467 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1468 which holds <a href="#description">additional extra text</a> to emit when the
1469 <tt>--help</tt> option is invoked.</p>
1473 <!-- _______________________________________________________________________ -->
1474 <div class="doc_subsubsection">
1475 <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
1479 <div class="doc_text">
1481 <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
1483 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
1484 except that it is designed to take values for options from an environment
1485 variable, for those cases in which reading the command line is not convenient or
1486 not desired. It fills in the values of all the command line option variables
1488 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
1491 <p>It takes three parameters: first, the name of the program (since
1492 <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
1493 second, the name of the environment variable to examine, and third, the optional
1494 <a href="#description">additional extra text</a> to emit when the
1495 <tt>--help</tt> option is invoked.</p>
1497 <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
1498 variable's value up into words and then process them using
1499 <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
1500 <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
1501 quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
1502 be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
1503 which is different from what you would get from the shell with the same
1508 <!-- _______________________________________________________________________ -->
1509 <div class="doc_subsubsection">
1510 <a name="cl::opt">The <tt>cl::opt</tt> class</a>
1513 <div class="doc_text">
1515 <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
1516 options, and is the one used most of the time. It is a templated class which
1517 can take up to three arguments (all except for the first have default values
1520 <div class="doc_code"><pre>
1521 <b>namespace</b> cl {
1522 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1523 <b>class</b> ParserClass = parser<DataType> >
1528 <p>The first template argument specifies what underlying data type the command
1529 line argument is, and is used to select a default parser implementation. The
1530 second template argument is used to specify whether the option should contain
1531 the storage for the option (the default) or whether external storage should be
1532 used to contain the value parsed for the option (see <a href="#storage">Internal
1533 vs External Storage</a> for more information).</p>
1535 <p>The third template argument specifies which parser to use. The default value
1536 selects an instantiation of the <tt>parser</tt> class based on the underlying
1537 data type of the option. In general, this default works well for most
1538 applications, so this option is only used when using a <a
1539 href="#customparser">custom parser</a>.</p>
1543 <!-- _______________________________________________________________________ -->
1544 <div class="doc_subsubsection">
1545 <a name="cl::list">The <tt>cl::list</tt> class</a>
1548 <div class="doc_text">
1550 <p>The <tt>cl::list</tt> class is the class used to represent a list of command
1551 line options. It too is a templated class which can take up to three
1554 <div class="doc_code"><pre>
1555 <b>namespace</b> cl {
1556 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1557 <b>class</b> ParserClass = parser<DataType> >
1562 <p>This class works the exact same as the <a
1563 href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
1564 the <b>type</b> of the external storage, not a boolean value. For this class,
1565 the marker type '<tt>bool</tt>' is used to indicate that internal storage should
1570 <!-- _______________________________________________________________________ -->
1571 <div class="doc_subsubsection">
1572 <a name="cl::bits">The <tt>cl::bits</tt> class</a>
1575 <div class="doc_text">
1577 <p>The <tt>cl::bits</tt> class is the class used to represent a list of command
1578 line options in the form of a bit vector. It is also a templated class which
1579 can take up to three arguments:</p>
1581 <div class="doc_code"><pre>
1582 <b>namespace</b> cl {
1583 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1584 <b>class</b> ParserClass = parser<DataType> >
1589 <p>This class works the exact same as the <a
1590 href="#cl::opt"><tt>cl::lists</tt></a> class, except that the second argument
1591 must be of <b>type</b> <tt>unsigned</tt> if external storage is used.</p>
1595 <!-- _______________________________________________________________________ -->
1596 <div class="doc_subsubsection">
1597 <a name="cl::alias">The <tt>cl::alias</tt> class</a>
1600 <div class="doc_text">
1602 <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1603 aliases for other arguments.</p>
1605 <div class="doc_code"><pre>
1606 <b>namespace</b> cl {
1611 <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
1612 used to specify which option this is an alias for. Alias arguments default to
1613 being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
1614 the conversion from string to data.</p>
1618 <!-- _______________________________________________________________________ -->
1619 <div class="doc_subsubsection">
1620 <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a>
1623 <div class="doc_text">
1625 <p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra
1626 help text to be printed out for the <tt>--help</tt> option.</p>
1628 <div class="doc_code"><pre>
1629 <b>namespace</b> cl {
1630 <b>struct</b> extrahelp;
1634 <p>To use the extrahelp, simply construct one with a <tt>const char*</tt>
1635 parameter to the constructor. The text passed to the constructor will be printed
1636 at the bottom of the help message, verbatim. Note that multiple
1637 <tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If
1638 your tool needs to print additional help information, put all that help into a
1639 single <tt>cl::extrahelp</tt> instance.</p>
1641 <div class="doc_code"><pre>
1642 cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
1646 <!-- ======================================================================= -->
1647 <div class="doc_subsection">
1648 <a name="builtinparsers">Builtin parsers</a>
1651 <div class="doc_text">
1653 <p>Parsers control how the string value taken from the command line is
1654 translated into a typed value, suitable for use in a C++ program. By default,
1655 the CommandLine library uses an instance of <tt>parser<type></tt> if the
1656 command line option specifies that it uses values of type '<tt>type</tt>'.
1657 Because of this, custom option processing is specified with specializations of
1658 the '<tt>parser</tt>' class.</p>
1660 <p>The CommandLine library provides the following builtin parser
1661 specializations, which are sufficient for most applications. It can, however,
1662 also be extended to work with new data types and new ways of interpreting the
1663 same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
1664 details on this type of library extension.</p>
1668 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
1669 can be used to map strings values to any data type, through the use of the <a
1670 href="#cl::values">cl::values</a> property, which specifies the mapping
1671 information. The most common use of this parser is for parsing enum values,
1672 which allows you to use the CommandLine library for all of the error checking to
1673 make sure that only valid enum values are specified (as opposed to accepting
1674 arbitrary strings). Despite this, however, the generic parser class can be used
1675 for any data type.</li>
1677 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
1678 is used to convert boolean strings to a boolean value. Currently accepted
1679 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1680 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
1682 <li><a name="stringparser">The <b><tt>parser<string></tt>
1683 specialization</b></a> simply stores the parsed string into the string value
1684 specified. No conversion or modification of the data is performed.</li>
1686 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
1687 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1688 accept a decimal number (with an optional '+' or '-' prefix) which must start
1689 with a non-zero digit. It accepts octal numbers, which are identified with a
1690 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1691 '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
1693 <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
1694 <b><tt>parser<float></tt> specializations</b> use the standard C
1695 <tt>strtod</tt> function to convert floating point strings into floating point
1696 values. As such, a broad range of string formats is supported, including
1697 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1704 <!-- *********************************************************************** -->
1705 <div class="doc_section">
1706 <a name="extensionguide">Extension Guide</a>
1708 <!-- *********************************************************************** -->
1710 <div class="doc_text">
1712 <p>Although the CommandLine library has a lot of functionality built into it
1713 already (as discussed previously), one of its true strengths lie in its
1714 extensibility. This section discusses how the CommandLine library works under
1715 the covers and illustrates how to do some simple, common, extensions.</p>
1719 <!-- ======================================================================= -->
1720 <div class="doc_subsection">
1721 <a name="customparser">Writing a custom parser</a>
1724 <div class="doc_text">
1726 <p>One of the simplest and most common extensions is the use of a custom parser.
1727 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1728 of the CommandLine library that turns string input from the user into a
1729 particular parsed data type, validating the input in the process.</p>
1731 <p>There are two ways to use a new parser:</p>
1737 <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1738 your custom data type.<p>
1740 <p>This approach has the advantage that users of your custom data type will
1741 automatically use your custom parser whenever they define an option with a value
1742 type of your data type. The disadvantage of this approach is that it doesn't
1743 work if your fundemental data type is something that is already supported.</p>
1749 <p>Write an independent class, using it explicitly from options that need
1752 <p>This approach works well in situations where you would line to parse an
1753 option using special syntax for a not-very-special data-type. The drawback of
1754 this approach is that users of your parser have to be aware that they are using
1755 your parser, instead of the builtin ones.</p>
1761 <p>To guide the discussion, we will discuss a custom parser that accepts file
1762 sizes, specified with an optional unit after the numeric size. For example, we
1763 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1764 this case, the underlying data type we want to parse into is
1765 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1766 this the default for all <tt>unsigned</tt> options.</p>
1768 <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
1770 <div class="doc_code"><pre>
1771 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1772 <i>// parse - Return true on error.</i>
1773 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1774 <b>unsigned</b> &Val);
1778 <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
1779 fill in the default, boiler plate, code for us. We give it the data type that
1780 we parse into (the last argument to the <tt>parse</tt> method so that clients of
1781 our custom parser know what object type to pass in to the parse method (here we
1782 declare that we parse into '<tt>unsigned</tt>' variables.</p>
1784 <p>For most purposes, the only method that must be implemented in a custom
1785 parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
1786 whenever the option is invoked, passing in the option itself, the option name,
1787 the string to parse, and a reference to a return value. If the string to parse
1788 is not well formed, the parser should output an error message and return true.
1789 Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
1790 our example, we implement <tt>parse</tt> as:</p>
1792 <div class="doc_code"><pre>
1793 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1794 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1795 <b>const char</b> *ArgStart = Arg.c_str();
1798 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1799 Val = (unsigned)strtol(ArgStart, &End, 0);
1802 <b>switch</b> (*End++) {
1803 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1804 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1805 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1808 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1809 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1810 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1813 <i>// Print an error message if unrecognized character!</i>
1814 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1820 <p>This function implements a very simple parser for the kinds of strings we are
1821 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1822 example), it is good enough for this example. Note that we use the option
1823 itself to print out the error message (the <tt>error</tt> method always returns
1824 true) in order to get a nice error message (shown below). Now that we have our
1825 parser class, we can use it like this:</p>
1827 <div class="doc_code"><pre>
1828 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1829 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1830 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1833 <p>Which adds this to the output of our program:</p>
1835 <div class="doc_code"><pre>
1837 -help - display available options (--help-hidden for more)
1839 <b>-max-file-size=<size> - Maximum file size to accept</b>
1842 <p>And we can test that our parse works correctly now (the test program just
1843 prints out the max-file-size argument value):</p>
1845 <div class="doc_code"><pre>
1848 $ ./test -max-file-size=123MB
1850 $ ./test -max-file-size=3G
1852 $ ./test -max-file-size=dog
1853 -max-file-size option: 'dog' value invalid for file size argument!
1856 <p>It looks like it works. The error message that we get is nice and helpful,
1857 and we seem to accept reasonable file sizes. This wraps up the "custom parser"
1862 <!-- ======================================================================= -->
1863 <div class="doc_subsection">
1864 <a name="explotingexternal">Exploiting external storage</a>
1867 <div class="doc_text">
1868 <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that
1869 will automatically be included in any program that links with that library.
1870 This is a feature. However, sometimes it is necessary to know the value of the
1871 command line option outside of the library. In these cases the library does or
1872 should provide an external storage location that is accessible to users of the
1873 library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the
1874 <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt>
1875 flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p>
1877 <p>TODO: complete this section</p>
1881 <!-- ======================================================================= -->
1882 <div class="doc_subsection">
1883 <a name="dynamicopts">Dynamically adding command line options</a>
1886 <div class="doc_text">
1888 <p>TODO: fill in this section</p>
1892 <!-- *********************************************************************** -->
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1901 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1902 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
1903 Last modified: $Date$