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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::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt>
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>
72 <li><a href="#builtinparsers">Builtin parsers</a>
74 <li><a href="#genericparser">The Generic <tt>parser<t></tt>
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>
88 <li><a href="#extensionguide">Extension Guide</a>
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
97 <div class="doc_author">
98 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
101 <!-- *********************************************************************** -->
102 <div class="doc_section">
103 <a name="introduction">Introduction</a>
105 <!-- *********************************************************************** -->
107 <div class="doc_text">
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
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>
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
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>
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
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>
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>
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>
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>
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
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>
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>
185 <!-- *********************************************************************** -->
186 <div class="doc_section">
187 <a name="quickstart">Quick Start Guide</a>
189 <!-- *********************************************************************** -->
191 <div class="doc_text">
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
198 <p>To start out, you need to include the CommandLine header file into your
201 <div class="doc_code"><pre>
202 #include "llvm/Support/CommandLine.h"
205 <p>Additionally, you need to add this as the first line of your main
208 <div class="doc_code"><pre>
209 int main(int argc, char **argv) {
210 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
215 <p>... which actually parses the arguments and fills in the variable
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 arguments 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>
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>"));
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>
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
244 <div class="doc_code"><pre>
245 USAGE: compiler [options]
248 -help - display available options (--help-hidden for more)
249 <b>-o <filename> - Specify output filename</b>
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
257 <div class="doc_code"><pre>
259 ofstream Output(OutputFilename.c_str());
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>
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>
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>"));
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>
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>);
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>
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>"));
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
313 <div class="doc_code"><pre>
314 USAGE: compiler [options] <b><input file></b>
317 -help - display available options (--help-hidden for more)
318 -o <filename> - Specify output filename
321 <p>... indicating that an input filename is expected.</p>
325 <!-- ======================================================================= -->
326 <div class="doc_subsection">
327 <a name="bool">Boolean Arguments</a>
330 <div class="doc_text">
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>
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>);
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>
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>
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
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>
374 <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
376 <div class="doc_code"><pre>
377 USAGE: compiler [options] <input file>
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)
386 <p>and "<tt>compiler --help-hidden</tt>" prints this:</p>
388 <div class="doc_code"><pre>
389 USAGE: compiler [options] <input file>
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)
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>
407 <!-- ======================================================================= -->
408 <div class="doc_subsection">
409 <a name="alias">Argument Aliases</a>
412 <div class="doc_text">
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>
417 <div class="doc_code"><pre>
419 if (!Quiet && !Quiet2) printInformationalMessage(...);
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
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));
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
443 <p>Now the application code can simply use:</p>
445 <div class="doc_code"><pre>
447 if (!Quiet) printInformationalMessage(...);
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
457 <!-- ======================================================================= -->
458 <div class="doc_subsection">
459 <a name="onealternative">Selecting an alternative from a set of
463 <div class="doc_text">
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>
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>
474 <p>Let's 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>
480 <li>A user could specify more than one of the options at a time, for example,
481 "<tt>compiler -O3 -O2</tt>". The CommandLine library would not be able to
482 catch this erroneous input for us.</li>
484 <li>We would have to test 4 different variables to see which ones are set.</li>
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>
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
495 <div class="doc_code"><pre>
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>"),
509 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
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
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>
523 <div class="doc_code"><pre>
524 USAGE: compiler [options] <input file>
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
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
543 <div class="doc_code"><pre>
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>"),
557 if (OptimizationLevel == Debug) outputDebugInfo(...);
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>
568 <!-- ======================================================================= -->
569 <div class="doc_subsection">
570 <a name="namedalternatives">Named Alternatives</a>
573 <div class="doc_text">
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>
584 <div class="doc_code"><pre>
586 nodebuginfo, quick, detailed
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>"),
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>
603 <div class="doc_code"><pre>
604 USAGE: compiler [options] <input file>
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
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>
630 <!-- ======================================================================= -->
631 <div class="doc_subsection">
632 <a name="list">Parsing a list of options</a>
635 <div class="doc_text">
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>
646 <div class="doc_code"><pre>
648 // 'inline' is a C++ keyword, so name it 'inlining'
649 dce, constprop, inlining, strip
653 <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
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>"),
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
669 <div class="doc_code"><pre>
670 for (unsigned i = 0; i != OptimizationList.size(); ++i)
671 switch (OptimizationList[i])
675 <p>... to iterate through the list of options specified.</p>
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>
685 <div class="doc_code"><pre>
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>);
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>
700 <!-- ======================================================================= -->
701 <div class="doc_subsection">
702 <a name="bits">Collecting options as a set of flags</a>
705 <div class="doc_text">
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
715 <div class="doc_code"><pre>
716 <i>bits</i> |= 1 << (unsigned)<i>enum</i>;
719 <p>Options that are specified multiple times are redundant. Any instances after
720 the first are discarded.</p>
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>
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>"),
735 <p>To test to see if <tt>constprop</tt> was specified, we can use the
736 <tt>cl:bits::isSet</tt> function:</p>
738 <div class="doc_code"><pre>
739 if (OptimizationBits.isSet(constprop)) {
744 <p>It's also possible to get the raw bit vector using the
745 <tt>cl::bits::getBits</tt> function:</p>
747 <div class="doc_code"><pre>
748 unsigned bits = OptimizationBits.getBits();
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 equivalent to a <a
754 href="#list"> <tt>cl::list</tt></a> option.</p>
759 <!-- ======================================================================= -->
760 <div class="doc_subsection">
761 <a name="description">Adding freeform text to help output</a>
764 <div class="doc_text">
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
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>
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");
785 <p>would yield the help output:</p>
787 <div class="doc_code"><pre>
788 <b>OVERVIEW: CommandLine compiler example
790 This program blah blah blah...</b>
792 USAGE: compiler [options] <input file>
796 -help - display available options (--help-hidden for more)
797 -o <filename> - Specify output filename
803 <!-- *********************************************************************** -->
804 <div class="doc_section">
805 <a name="referenceguide">Reference Guide</a>
807 <!-- *********************************************************************** -->
809 <div class="doc_text">
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>
818 <!-- ======================================================================= -->
819 <div class="doc_subsection">
820 <a name="positional">Positional Arguments</a>
823 <div class="doc_text">
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>
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>"));
837 <p>Given these two option declarations, the <tt>--help</tt> output for our grep
838 replacement would look like this:</p>
840 <div class="doc_code"><pre>
841 USAGE: spiffygrep [options] <b><regular expression> <input file></b>
844 -help - display available options (--help-hidden for more)
847 <p>... and the resultant program could be used just like the standard
848 <tt>grep</tt> tool.</p>
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>
859 <!-- _______________________________________________________________________ -->
860 <div class="doc_subsubsection">
861 <a name="--">Specifying positional options with hyphens</a>
864 <div class="doc_text">
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>
872 <div class="doc_code"><pre>
873 $ spiffygrep '-foo' test.txt
874 Unknown command line argument '-foo'. Try: spiffygrep --help'
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 . . .
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>
889 <div class="doc_code"><pre>
890 $ spiffygrep -- -foo test.txt
896 <!-- _______________________________________________________________________ -->
897 <div class="doc_subsubsection">
898 <a name="getPosition">Determining absolute position with getPosition()</a>
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
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>
917 <div class="doc_code"><pre>
918 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
919 static cl::list<std::string> Libraries("l", cl::ZeroOrMore);
921 int main(int argc, char**argv) {
923 std::vector<std::string>::iterator fileIt = Files.begin();
924 std::vector<std::string>::iterator libIt = Libraries.begin();
925 unsigned libPos = 0, filePos = 0;
927 if ( libIt != Libraries.end() )
928 libPos = Libraries.getPosition( libIt - Libraries.begin() );
931 if ( fileIt != Files.end() )
932 filePos = Files.getPosition( fileIt - Files.begin() );
936 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
937 // Source File Is next
940 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
945 break; // we're done with the list
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>
955 <!-- _______________________________________________________________________ -->
956 <div class="doc_subsubsection">
957 <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
960 <div class="doc_text">
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>
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>
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>"));
982 <p>which automatically provides the help output:</p>
984 <div class="doc_code"><pre>
985 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
988 -help - display available options (--help-hidden for more)
989 <b>-x - Enable trace output</b>
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
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>
1008 <!-- ======================================================================= -->
1009 <div class="doc_subsection">
1010 <a name="storage">Internal vs External Storage</a>
1013 <div class="doc_text">
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>
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>
1029 <p>To do this, set up your .h file with your option, like this for example:</p>
1031 <div class="doc_code">
1033 <i>// DebugFlag.h - Get access to the '-debug' command line option
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.
1040 extern bool DebugFlag;
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.</i>
1046 <span class="doc_hilite">#ifdef NDEBUG
1049 #define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0)
1050 <span class="doc_hilite">#endif</span>
1054 <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
1055 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
1056 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
1057 an additional argument to our command line argument processor, and we specify
1058 where to fill in with the <a href="#cl::location">cl::location</a>
1061 <div class="doc_code">
1063 bool DebugFlag; <i>// the actual value</i>
1064 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
1065 Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>, <a href="#cl::location">cl::location</a>(DebugFlag));
1069 <p>In the above example, we specify "<tt>true</tt>" as the second argument to
1070 the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the
1071 template should not maintain a copy of the value itself. In addition to this,
1072 we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so
1073 that <tt>DebugFlag</tt> is automatically set.</p>
1077 <!-- ======================================================================= -->
1078 <div class="doc_subsection">
1079 <a name="attributes">Option Attributes</a>
1082 <div class="doc_text">
1084 <p>This section describes the basic attributes that you can specify on
1089 <li>The option name attribute (which is required for all options, except <a
1090 href="#positional">positional options</a>) specifies what the option name is.
1091 This option is specified in simple double quotes:
1094 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
1099 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
1100 description for the option to be shown in the <tt>--help</tt> output for the
1103 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
1104 specifies a string that can be used to fine tune the <tt>--help</tt> output for
1105 a command line option. Look <a href="#value_desc_example">here</a> for an
1108 <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
1109 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
1110 not specified then the command line option value defaults to the value created
1111 by the default constructor for the type. <b>Warning</b>: If you specify both
1112 <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
1113 you must specify <b><tt>cl::location</tt></b> first, so that when the
1114 command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
1115 initial value. (You will get an error at runtime if you don't put them in
1116 the right order.)</li>
1118 <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
1119 store the value for a parsed command line option if using external storage. See
1120 the section on <a href="#storage">Internal vs External Storage</a> for more
1123 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
1124 specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is
1127 <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
1128 the string-to-value mapping to be used by the generic parser. It takes a
1129 <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
1131 specify the option name, the value mapped to, and the description shown in the
1132 <tt>--help</tt> for the tool. Because the generic parser is used most
1133 frequently with enum values, two macros are often useful:
1137 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
1138 nice simple way to specify a triplet for an enum. This macro automatically
1139 makes the option name be the same as the enum name. The first option to the
1140 macro is the enum, the second is the description for the command line
1143 <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
1144 specify macro options where the option name doesn't equal the enum name. For
1145 this macro, the first argument is the enum value, the second is the flag name,
1146 and the second is the description.</li>
1150 You will get a compile time error if you try to use cl::values with a parser
1151 that does not support it.</li>
1157 <!-- ======================================================================= -->
1158 <div class="doc_subsection">
1159 <a name="modifiers">Option Modifiers</a>
1162 <div class="doc_text">
1164 <p>Option modifiers are the flags and expressions that you pass into the
1165 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1166 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
1167 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
1168 your application well.</p>
1170 <p>These options fall into five main catagories:</p>
1173 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
1174 <li><a href="#numoccurrences">Controlling the number of occurrences
1175 required and allowed</a></li>
1176 <li><a href="#valrequired">Controlling whether or not a value must be
1178 <li><a href="#formatting">Controlling other formatting options</a></li>
1179 <li><a href="#misc">Miscellaneous option modifiers</a></li>
1182 <p>It is not possible to specify two options from the same catagory (you'll get
1183 a runtime error) to a single option, except for options in the miscellaneous
1184 catagory. The CommandLine library specifies defaults for all of these settings
1185 that are the most useful in practice and the most common, which mean that you
1186 usually shouldn't have to worry about these.</p>
1190 <!-- _______________________________________________________________________ -->
1191 <div class="doc_subsubsection">
1192 <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
1195 <div class="doc_text">
1197 <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
1198 <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
1199 appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
1200 compiled program:</p>
1204 <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
1205 (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1206 href="#cl::list">cl::list</a></tt> options) indicates the option is to appear
1207 in both help listings.</li>
1209 <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
1210 default for <tt><a href="#cl::alias">cl::alias</a></tt> options) indicates that
1211 the option should not appear in the <tt>--help</tt> output, but should appear in
1212 the <tt>--help-hidden</tt> output.</li>
1214 <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier
1215 indicates that the option should not appear in any help output.</li>
1221 <!-- _______________________________________________________________________ -->
1222 <div class="doc_subsubsection">
1223 <a name="numoccurrences">Controlling the number of occurrences required and
1227 <div class="doc_text">
1229 <p>This group of options is used to control how many time an option is allowed
1230 (or required) to be specified on the command line of your program. Specifying a
1231 value for this setting allows the CommandLine library to do error checking for
1234 <p>The allowed values for this option group are:</p>
1238 <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
1239 is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1240 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1241 allow either zero or one occurrence of the option to be specified.</li>
1243 <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
1244 (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
1245 indicates that your program will allow the option to be specified zero or more
1248 <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
1249 indicates that the specified option must be specified exactly one time.</li>
1251 <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
1252 indicates that the option must be specified at least one time.</li>
1254 <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1255 href="#positional">Positional arguments section</a>.</li>
1259 <p>If an option is not specified, then the value of the option is equal to the
1260 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1261 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1262 option value is initialized with the default constructor for the data type.</p>
1264 <p>If an option is specified multiple times for an option of the <tt><a
1265 href="#cl::opt">cl::opt</a></tt> class, only the last value will be
1270 <!-- _______________________________________________________________________ -->
1271 <div class="doc_subsubsection">
1272 <a name="valrequired">Controlling whether or not a value must be specified</a>
1275 <div class="doc_text">
1277 <p>This group of options is used to control whether or not the option allows a
1278 value to be present. In the case of the CommandLine library, a value is either
1279 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1280 string (e.g. '<tt>-o a.out</tt>').</p>
1282 <p>The allowed values for this option group are:</p>
1286 <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
1287 (which is the default for <tt>bool</tt> typed options) specifies that it is
1288 acceptable to have a value, or not. A boolean argument can be enabled just by
1289 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1290 If an option is specified with this mode, it is illegal for the value to be
1291 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1292 get this behavior, you must use the <a
1293 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
1295 <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
1296 (which is the default for all other types except for <a
1297 href="#onealternative">unnamed alternatives using the generic parser</a>)
1298 specifies that a value must be provided. This mode informs the command line
1299 library that if an option is not provides with an equal sign, that the next
1300 argument provided must be the value. This allows things like '<tt>-o
1301 a.out</tt>' to work.</li>
1303 <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
1304 modifier (which is the default for <a href="#onealternative">unnamed
1305 alternatives using the generic parser</a>) indicates that it is a runtime error
1306 for the user to specify a value. This can be provided to disallow users from
1307 providing options to boolean options (like '<tt>-foo=true</tt>').</li>
1311 <p>In general, the default values for this option group work just like you would
1312 want them to. As mentioned above, you can specify the <a
1313 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1314 argument to restrict your command line parser. These options are mostly useful
1315 when <a href="#extensionguide">extending the library</a>.</p>
1319 <!-- _______________________________________________________________________ -->
1320 <div class="doc_subsubsection">
1321 <a name="formatting">Controlling other formatting options</a>
1324 <div class="doc_text">
1326 <p>The formatting option group is used to specify that the command line option
1327 has special abilities and is otherwise different from other command line
1328 arguments. As usual, you can only specify one of these arguments at most.</p>
1332 <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
1333 modifier (which is the default all options) specifies that this option is
1336 <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
1337 specifies that this is a positional argument that does not have a command line
1338 option associated with it. See the <a href="#positional">Positional
1339 Arguments</a> section for more information.</li>
1341 <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1342 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
1344 <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
1345 that this option prefixes its value. With 'Prefix' options, the equal sign does
1346 not separate the value from the option name specified. Instead, the value is
1347 everything after the prefix, including any equal sign if present. This is useful
1348 for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a
1349 linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the
1350 '<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list)
1351 options, that have the <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b>
1352 modifier added to allow the CommandLine library to recognize them. Note that
1353 <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> options must not have the
1354 <b><tt><a href="#cl::ValueDisallowed">cl::ValueDisallowed</a></tt></b> modifier
1357 <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
1358 to implement Unix-style tools (like <tt>ls</tt>) that have lots of single letter
1359 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1360 command actually enables four different options, all of which are single
1361 letters. Note that <b><tt><a href="#cl::Grouping">cl::Grouping</a></tt></b>
1362 options cannot have values.</li>
1366 <p>The CommandLine library does not restrict how you use the <b><tt><a
1367 href="#cl::Prefix">cl::Prefix</a></tt></b> or <b><tt><a
1368 href="#cl::Grouping">cl::Grouping</a></tt></b> modifiers, but it is possible to
1369 specify ambiguous argument settings. Thus, it is possible to have multiple
1370 letter options that are prefix or grouping options, and they will still work as
1373 <p>To do this, the CommandLine library uses a greedy algorithm to parse the
1374 input option into (potentially multiple) prefix and grouping options. The
1375 strategy basically looks like this:</p>
1377 <div class="doc_code"><tt>parse(string OrigInput) {</tt>
1380 <li><tt>string input = OrigInput;</tt>
1381 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1382 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1383 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1384 <li><tt>if (getOption(input).isPrefix())<br>
1385 return getOption(input).parse(input);</tt>
1386 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1387 getOption(input).parse();<br>
1388 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1389 input = OrigInput;<br>
1390 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1392 <li><tt>if (!OrigInput.empty()) error();</tt></li>
1400 <!-- _______________________________________________________________________ -->
1401 <div class="doc_subsubsection">
1402 <a name="misc">Miscellaneous option modifiers</a>
1405 <div class="doc_text">
1407 <p>The miscellaneous option modifiers are the only flags where you can specify
1408 more than one flag from the set: they are not mutually exclusive. These flags
1409 specify boolean properties that modify the option.</p>
1413 <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
1414 indicates that any commas specified for an option's value should be used to
1415 split the value up into multiple values for the option. For example, these two
1416 options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
1417 "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
1418 makes sense to be used in a case where the option is allowed to accept one or
1419 more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
1421 <li><a name="cl::PositionalEatsArgs">The
1422 <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
1423 positional arguments, and only makes sense for lists) indicates that positional
1424 argument should consume any strings after it (including strings that start with
1425 a "-") up until another recognized positional argument. For example, if you
1426 have two "eating" positional arguments, "<tt>pos1</tt>" and "<tt>pos2</tt>", the
1427 string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
1428 -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
1429 "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
1433 <p>So far, these are the only two miscellaneous option modifiers.</p>
1437 <!-- ======================================================================= -->
1438 <div class="doc_subsection">
1439 <a name="toplevel">Top-Level Classes and Functions</a>
1442 <div class="doc_text">
1444 <p>Despite all of the built-in flexibility, the CommandLine option library
1445 really only consists of one function (<a
1446 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1447 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1448 href="#cl::list"><tt>cl::list</tt></a>, and <a
1449 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1450 classes in detail.</p>
1454 <!-- _______________________________________________________________________ -->
1455 <div class="doc_subsubsection">
1456 <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
1460 <div class="doc_text">
1462 <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1463 directly from <tt>main</tt>, and is used to fill in the values of all of the
1464 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1467 <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1468 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1469 which holds <a href="#description">additional extra text</a> to emit when the
1470 <tt>--help</tt> option is invoked.</p>
1474 <!-- _______________________________________________________________________ -->
1475 <div class="doc_subsubsection">
1476 <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
1480 <div class="doc_text">
1482 <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
1484 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
1485 except that it is designed to take values for options from an environment
1486 variable, for those cases in which reading the command line is not convenient or
1487 desired. It fills in the values of all the command line option variables just
1489 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
1492 <p>It takes three parameters: the name of the program (since <tt>argv</tt> may
1493 not be available, it can't just look in <tt>argv[0]</tt>), the name of the
1494 environment variable to examine, and the optional
1495 <a href="#description">additional extra text</a> to emit when the
1496 <tt>--help</tt> option is invoked.</p>
1498 <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
1499 variable's value up into words and then process them using
1500 <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
1501 <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
1502 quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
1503 be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
1504 which is different from what you would get from the shell with the same
1509 <!-- _______________________________________________________________________ -->
1510 <div class="doc_subsubsection">
1511 <a name="cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt>
1515 <div class="doc_text">
1517 <p>The <tt>cl::SetVersionPrinter</tt> function is designed to be called
1518 directly from <tt>main</tt> and <i>before</i>
1519 <tt>cl::ParseCommandLineOptions</tt>. Its use is optional. It simply arranges
1520 for a function to be called in response to the <tt>--version</tt> option instead
1521 of having the <tt>CommandLine</tt> library print out the usual version string
1522 for LLVM. This is useful for programs that are not part of LLVM but wish to use
1523 the <tt>CommandLine</tt> facilities. Such programs should just define a small
1524 function that takes no arguments and returns <tt>void</tt> and that prints out
1525 whatever version information is appropriate for the program. Pass the address
1526 of that function to <tt>cl::SetVersionPrinter</tt> to arrange for it to be
1527 called when the <tt>--version</tt> option is given by the user.</p>
1530 <!-- _______________________________________________________________________ -->
1531 <div class="doc_subsubsection">
1532 <a name="cl::opt">The <tt>cl::opt</tt> class</a>
1535 <div class="doc_text">
1537 <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
1538 options, and is the one used most of the time. It is a templated class which
1539 can take up to three arguments (all except for the first have default values
1542 <div class="doc_code"><pre>
1543 <b>namespace</b> cl {
1544 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1545 <b>class</b> ParserClass = parser<DataType> >
1550 <p>The first template argument specifies what underlying data type the command
1551 line argument is, and is used to select a default parser implementation. The
1552 second template argument is used to specify whether the option should contain
1553 the storage for the option (the default) or whether external storage should be
1554 used to contain the value parsed for the option (see <a href="#storage">Internal
1555 vs External Storage</a> for more information).</p>
1557 <p>The third template argument specifies which parser to use. The default value
1558 selects an instantiation of the <tt>parser</tt> class based on the underlying
1559 data type of the option. In general, this default works well for most
1560 applications, so this option is only used when using a <a
1561 href="#customparser">custom parser</a>.</p>
1565 <!-- _______________________________________________________________________ -->
1566 <div class="doc_subsubsection">
1567 <a name="cl::list">The <tt>cl::list</tt> class</a>
1570 <div class="doc_text">
1572 <p>The <tt>cl::list</tt> class is the class used to represent a list of command
1573 line options. It too is a templated class which can take up to three
1576 <div class="doc_code"><pre>
1577 <b>namespace</b> cl {
1578 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1579 <b>class</b> ParserClass = parser<DataType> >
1584 <p>This class works the exact same as the <a
1585 href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
1586 the <b>type</b> of the external storage, not a boolean value. For this class,
1587 the marker type '<tt>bool</tt>' is used to indicate that internal storage should
1592 <!-- _______________________________________________________________________ -->
1593 <div class="doc_subsubsection">
1594 <a name="cl::bits">The <tt>cl::bits</tt> class</a>
1597 <div class="doc_text">
1599 <p>The <tt>cl::bits</tt> class is the class used to represent a list of command
1600 line options in the form of a bit vector. It is also a templated class which
1601 can take up to three arguments:</p>
1603 <div class="doc_code"><pre>
1604 <b>namespace</b> cl {
1605 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1606 <b>class</b> ParserClass = parser<DataType> >
1611 <p>This class works the exact same as the <a
1612 href="#cl::opt"><tt>cl::lists</tt></a> class, except that the second argument
1613 must be of <b>type</b> <tt>unsigned</tt> if external storage is used.</p>
1617 <!-- _______________________________________________________________________ -->
1618 <div class="doc_subsubsection">
1619 <a name="cl::alias">The <tt>cl::alias</tt> class</a>
1622 <div class="doc_text">
1624 <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1625 aliases for other arguments.</p>
1627 <div class="doc_code"><pre>
1628 <b>namespace</b> cl {
1633 <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
1634 used to specify which option this is an alias for. Alias arguments default to
1635 being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
1636 the conversion from string to data.</p>
1640 <!-- _______________________________________________________________________ -->
1641 <div class="doc_subsubsection">
1642 <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a>
1645 <div class="doc_text">
1647 <p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra
1648 help text to be printed out for the <tt>--help</tt> option.</p>
1650 <div class="doc_code"><pre>
1651 <b>namespace</b> cl {
1652 <b>struct</b> extrahelp;
1656 <p>To use the extrahelp, simply construct one with a <tt>const char*</tt>
1657 parameter to the constructor. The text passed to the constructor will be printed
1658 at the bottom of the help message, verbatim. Note that multiple
1659 <tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If
1660 your tool needs to print additional help information, put all that help into a
1661 single <tt>cl::extrahelp</tt> instance.</p>
1663 <div class="doc_code"><pre>
1664 cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
1668 <!-- ======================================================================= -->
1669 <div class="doc_subsection">
1670 <a name="builtinparsers">Builtin parsers</a>
1673 <div class="doc_text">
1675 <p>Parsers control how the string value taken from the command line is
1676 translated into a typed value, suitable for use in a C++ program. By default,
1677 the CommandLine library uses an instance of <tt>parser<type></tt> if the
1678 command line option specifies that it uses values of type '<tt>type</tt>'.
1679 Because of this, custom option processing is specified with specializations of
1680 the '<tt>parser</tt>' class.</p>
1682 <p>The CommandLine library provides the following builtin parser
1683 specializations, which are sufficient for most applications. It can, however,
1684 also be extended to work with new data types and new ways of interpreting the
1685 same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
1686 details on this type of library extension.</p>
1690 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
1691 can be used to map strings values to any data type, through the use of the <a
1692 href="#cl::values">cl::values</a> property, which specifies the mapping
1693 information. The most common use of this parser is for parsing enum values,
1694 which allows you to use the CommandLine library for all of the error checking to
1695 make sure that only valid enum values are specified (as opposed to accepting
1696 arbitrary strings). Despite this, however, the generic parser class can be used
1697 for any data type.</li>
1699 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
1700 is used to convert boolean strings to a boolean value. Currently accepted
1701 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1702 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
1704 <li><a name="boolOrDefaultparser">The <b><tt>parser<boolOrDefault></tt>
1705 specialization</b></a> is used for cases where the value is boolean,
1706 but we also need to know whether the option was specified at all. boolOrDefault
1707 is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. This parser accepts
1708 the same strings as <b><tt>parser<bool></tt></b>.</li>
1710 <li><a name="stringparser">The <b><tt>parser<string></tt>
1711 specialization</b></a> simply stores the parsed string into the string value
1712 specified. No conversion or modification of the data is performed.</li>
1714 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
1715 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1716 accept a decimal number (with an optional '+' or '-' prefix) which must start
1717 with a non-zero digit. It accepts octal numbers, which are identified with a
1718 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1719 '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
1721 <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
1722 <b><tt>parser<float></tt> specializations</b> use the standard C
1723 <tt>strtod</tt> function to convert floating point strings into floating point
1724 values. As such, a broad range of string formats is supported, including
1725 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1732 <!-- *********************************************************************** -->
1733 <div class="doc_section">
1734 <a name="extensionguide">Extension Guide</a>
1736 <!-- *********************************************************************** -->
1738 <div class="doc_text">
1740 <p>Although the CommandLine library has a lot of functionality built into it
1741 already (as discussed previously), one of its true strengths lie in its
1742 extensibility. This section discusses how the CommandLine library works under
1743 the covers and illustrates how to do some simple, common, extensions.</p>
1747 <!-- ======================================================================= -->
1748 <div class="doc_subsection">
1749 <a name="customparser">Writing a custom parser</a>
1752 <div class="doc_text">
1754 <p>One of the simplest and most common extensions is the use of a custom parser.
1755 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1756 of the CommandLine library that turns string input from the user into a
1757 particular parsed data type, validating the input in the process.</p>
1759 <p>There are two ways to use a new parser:</p>
1765 <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1766 your custom data type.<p>
1768 <p>This approach has the advantage that users of your custom data type will
1769 automatically use your custom parser whenever they define an option with a value
1770 type of your data type. The disadvantage of this approach is that it doesn't
1771 work if your fundamental data type is something that is already supported.</p>
1777 <p>Write an independent class, using it explicitly from options that need
1780 <p>This approach works well in situations where you would line to parse an
1781 option using special syntax for a not-very-special data-type. The drawback of
1782 this approach is that users of your parser have to be aware that they are using
1783 your parser instead of the builtin ones.</p>
1789 <p>To guide the discussion, we will discuss a custom parser that accepts file
1790 sizes, specified with an optional unit after the numeric size. For example, we
1791 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1792 this case, the underlying data type we want to parse into is
1793 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1794 this the default for all <tt>unsigned</tt> options.</p>
1796 <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
1798 <div class="doc_code"><pre>
1799 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1800 <i>// parse - Return true on error.</i>
1801 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1802 <b>unsigned</b> &Val);
1806 <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
1807 fill in the default, boiler plate code for us. We give it the data type that
1808 we parse into, the last argument to the <tt>parse</tt> method, so that clients of
1809 our custom parser know what object type to pass in to the parse method. (Here we
1810 declare that we parse into '<tt>unsigned</tt>' variables.)</p>
1812 <p>For most purposes, the only method that must be implemented in a custom
1813 parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
1814 whenever the option is invoked, passing in the option itself, the option name,
1815 the string to parse, and a reference to a return value. If the string to parse
1816 is not well-formed, the parser should output an error message and return true.
1817 Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
1818 our example, we implement <tt>parse</tt> as:</p>
1820 <div class="doc_code"><pre>
1821 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1822 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1823 <b>const char</b> *ArgStart = Arg.c_str();
1826 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1827 Val = (unsigned)strtol(ArgStart, &End, 0);
1830 <b>switch</b> (*End++) {
1831 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1832 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1833 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1836 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1837 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1838 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1841 <i>// Print an error message if unrecognized character!</i>
1842 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1848 <p>This function implements a very simple parser for the kinds of strings we are
1849 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1850 example), it is good enough for this example. Note that we use the option
1851 itself to print out the error message (the <tt>error</tt> method always returns
1852 true) in order to get a nice error message (shown below). Now that we have our
1853 parser class, we can use it like this:</p>
1855 <div class="doc_code"><pre>
1856 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1857 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1858 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1861 <p>Which adds this to the output of our program:</p>
1863 <div class="doc_code"><pre>
1865 -help - display available options (--help-hidden for more)
1867 <b>-max-file-size=<size> - Maximum file size to accept</b>
1870 <p>And we can test that our parse works correctly now (the test program just
1871 prints out the max-file-size argument value):</p>
1873 <div class="doc_code"><pre>
1876 $ ./test -max-file-size=123MB
1878 $ ./test -max-file-size=3G
1880 $ ./test -max-file-size=dog
1881 -max-file-size option: 'dog' value invalid for file size argument!
1884 <p>It looks like it works. The error message that we get is nice and helpful,
1885 and we seem to accept reasonable file sizes. This wraps up the "custom parser"
1890 <!-- ======================================================================= -->
1891 <div class="doc_subsection">
1892 <a name="explotingexternal">Exploiting external storage</a>
1895 <div class="doc_text">
1896 <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that
1897 will automatically be included in any program that links with that library.
1898 This is a feature. However, sometimes it is necessary to know the value of the
1899 command line option outside of the library. In these cases the library does or
1900 should provide an external storage location that is accessible to users of the
1901 library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the
1902 <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt>
1903 flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p>
1905 <p>TODO: complete this section</p>
1909 <!-- ======================================================================= -->
1910 <div class="doc_subsection">
1911 <a name="dynamicopts">Dynamically adding command line options</a>
1914 <div class="doc_text">
1916 <p>TODO: fill in this section</p>
1920 <!-- *********************************************************************** -->
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1929 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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