1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
5 <title>CommandLine 2.0 Library Manual</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
10 <div class="doc_title">
11 CommandLine 2.0 Library Manual
15 <li><a href="#introduction">Introduction</a></li>
17 <li><a href="#quickstart">Quick Start Guide</a>
19 <li><a href="#bool">Boolean Arguments</a></li>
20 <li><a href="#alias">Argument Aliases</a></li>
21 <li><a href="#onealternative">Selecting an alternative from a
22 set of possibilities</a></li>
23 <li><a href="#namedalternatives">Named alternatives</a></li>
24 <li><a href="#list">Parsing a list of options</a></li>
25 <li><a href="#description">Adding freeform text to help output</a></li>
28 <li><a href="#referenceguide">Reference Guide</a>
30 <li><a href="#positional">Positional Arguments</a>
32 <li><a href="#--">Specifying positional options with hyphens</a></li>
33 <li><a href="#getPosition">Determining absolute position with
35 <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
39 <li><a href="#storage">Internal vs External Storage</a></li>
41 <li><a href="#attributes">Option Attributes</a></li>
43 <li><a href="#modifiers">Option Modifiers</a>
45 <li><a href="#hiding">Hiding an option from <tt>--help</tt>
47 <li><a href="#numoccurrences">Controlling the number of occurrences
48 required and allowed</a></li>
49 <li><a href="#valrequired">Controlling whether or not a value must be
51 <li><a href="#formatting">Controlling other formatting options</a></li>
52 <li><a href="#misc">Miscellaneous option modifiers</a></li>
55 <li><a href="#toplevel">Top-Level Classes and Functions</a>
57 <li><a href="#cl::ParseCommandLineOptions">The
58 <tt>cl::ParseCommandLineOptions</tt> function</a></li>
59 <li><a href="#cl::ParseEnvironmentOptions">The
60 <tt>cl::ParseEnvironmentOptions</tt> function</a></li>
61 <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li>
62 <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li>
63 <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li>
66 <li><a href="#builtinparsers">Builtin parsers</a>
68 <li><a href="#genericparser">The Generic <tt>parser<t></tt>
70 <li><a href="#boolparser">The <tt>parser<bool></tt>
71 specialization</a></li>
72 <li><a href="#stringparser">The <tt>parser<string></tt>
73 specialization</a></li>
74 <li><a href="#intparser">The <tt>parser<int></tt>
75 specialization</a></li>
76 <li><a href="#doubleparser">The <tt>parser<double></tt> and
77 <tt>parser<float></tt> specializations</a></li>
80 <li><a href="#extensionguide">Extension Guide</a>
82 <li><a href="#customparser">Writing a custom parser</a></li>
83 <li><a href="#explotingexternal">Exploiting external storage</a></li>
84 <li><a href="#dynamicopts">Dynamically adding command line
89 <div class="doc_author">
90 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
93 <!-- *********************************************************************** -->
94 <div class="doc_section">
95 <a name="introduction">Introduction</a>
97 <!-- *********************************************************************** -->
99 <div class="doc_text">
101 <p>This document describes the CommandLine argument processing library. It will
102 show you how to use it, and what it can do. The CommandLine library uses a
103 declarative approach to specifying the command line options that your program
104 takes. By default, these options declarations implicitly hold the value parsed
105 for the option declared (of course this <a href="#storage">can be
108 <p>Although there are a <b>lot</b> of command line argument parsing libraries
109 out there in many different languages, none of them fit well with what I needed.
110 By looking at the features and problems of other libraries, I designed the
111 CommandLine library to have the following features:</p>
114 <li>Speed: The CommandLine library is very quick and uses little resources. The
115 parsing time of the library is directly proportional to the number of arguments
116 parsed, not the the number of options recognized. Additionally, command line
117 argument values are captured transparently into user defined global variables,
118 which can be accessed like any other variable (and with the same
121 <li>Type Safe: As a user of CommandLine, you don't have to worry about
122 remembering the type of arguments that you want (is it an int? a string? a
123 bool? an enum?) and keep casting it around. Not only does this help prevent
124 error prone constructs, it also leads to dramatically cleaner source code.</li>
126 <li>No subclasses required: To use CommandLine, you instantiate variables that
127 correspond to the arguments that you would like to capture, you don't subclass a
128 parser. This means that you don't have to write <b>any</b> boilerplate
131 <li>Globally accessible: Libraries can specify command line arguments that are
132 automatically enabled in any tool that links to the library. This is possible
133 because the application doesn't have to keep a "list" of arguments to pass to
134 the parser. This also makes supporting <a href="#dynamicopts">dynamically
135 loaded options</a> trivial.</li>
137 <li>Cleaner: CommandLine supports enum and other types directly, meaning that
138 there is less error and more security built into the library. You don't have to
139 worry about whether your integral command line argument accidentally got
140 assigned a value that is not valid for your enum type.</li>
142 <li>Powerful: The CommandLine library supports many different types of
143 arguments, from simple <a href="#boolparser">boolean flags</a> to <a
144 href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
145 href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
146 href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
147 arguments</a>. This is possible because CommandLine is...</li>
149 <li>Extensible: It is very simple to add a new argument type to CommandLine.
150 Simply specify the parser that you want to use with the command line option when
151 you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li>
153 <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
154 that you, the user, have to do. For example, it automatically provides a
155 <tt>--help</tt> option that shows the available command line options for your
156 tool. Additionally, it does most of the basic correctness checking for
159 <li>Capable: The CommandLine library can handle lots of different forms of
160 options often found in real programs. For example, <a
161 href="#positional">positional</a> arguments, <tt>ls</tt> style <a
162 href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
163 -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
164 options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
165 href="#cl::ConsumeAfter">interpreter style options</a>.</li>
169 <p>This document will hopefully let you jump in and start using CommandLine in
170 your utility quickly and painlessly. Additionally it should be a simple
171 reference manual to figure out how stuff works. If it is failing in some area
172 (or you want an extension to the library), nag the author, <a
173 href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
177 <!-- *********************************************************************** -->
178 <div class="doc_section">
179 <a name="quickstart">Quick Start Guide</a>
181 <!-- *********************************************************************** -->
183 <div class="doc_text">
185 <p>This section of the manual runs through a simple CommandLine'ification of a
186 basic compiler tool. This is intended to show you how to jump into using the
187 CommandLine library in your own program, and show you some of the cool things it
190 <p>To start out, you need to include the CommandLine header file into your
194 #include "Support/CommandLine.h"
197 <p>Additionally, you need to add this as the first line of your main
201 int main(int argc, char **argv) {
202 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
207 <p>... which actually parses the arguments and fills in the variable
210 <p>Now that you are ready to support command line arguments, we need to tell the
211 system which ones we want, and what type of argument they are. The CommandLine
212 library uses a declarative syntax to model command line arguments with the
213 global variable declarations that capture the parsed values. This means that
214 for every command line option that you would like to support, there should be a
215 global variable declaration to capture the result. For example, in a compiler,
216 we would like to support the unix standard '<tt>-o <filename></tt>' option
217 to specify where to put the output. With the CommandLine library, this is
218 represented like this:</p>
220 <a name="value_desc_example"></a>
222 <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>"));
225 <p>This declares a global variable "<tt>OutputFilename</tt>" that is used to
226 capture the result of the "<tt>o</tt>" argument (first parameter). We specify
227 that this is a simple scalar option by using the "<tt><a
228 href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a
229 href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library
230 that the data type that we are parsing is a string.</p>
232 <p>The second and third parameters (which are optional) are used to specify what
233 to output for the "<tt>--help</tt>" option. In this case, we get a line that
237 USAGE: compiler [options]
240 -help - display available options (--help-hidden for more)
241 <b>-o <filename> - Specify output filename</b>
244 <p>Because we specified that the command line option should parse using the
245 <tt>string</tt> data type, the variable declared is automatically usable as a
246 real string in all contexts that a normal C++ string object may be used. For
251 ofstream Output(OutputFilename.c_str());
256 <p>There are many different options that you can use to customize the command
257 line option handling library, but the above example shows the general interface
258 to these options. The options can be specified in any order, and are specified
259 with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
260 there are no positional dependencies to remember. The available options are
261 discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p>
263 <p>Continuing the example, we would like to have our compiler take an input
264 filename as well as an output filename, but we do not want the input filename to
265 be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
266 style of argument, the CommandLine library allows for <a
267 href="#positional">positional</a> arguments to be specified for the program.
268 These positional arguments are filled with command line parameters that are not
269 in option form. We use this feature like this:</p>
272 <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>"));
275 <p>This declaration indicates that the first positional argument should be
276 treated as the input filename. Here we use the <tt><a
277 href="#cl::init">cl::init</a></tt> option to specify an initial value for the
278 command line option, which is used if the option is not specified (if you do not
279 specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
280 the default constructor for the data type is used to initialize the value).
281 Command line options default to being optional, so if we would like to require
282 that the user always specify an input filename, we would add the <tt><a
283 href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
284 <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p>
287 <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>);
290 <p>Again, the CommandLine library does not require the options to be specified
291 in any particular order, so the above declaration is equivalent to:</p>
294 <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>"));
297 <p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag,
298 the CommandLine library will automatically issue an error if the argument is not
299 specified, which shifts all of the command line option verification code out of
300 your application into the library. This is just one example of how using flags
301 can alter the default behaviour of the library, on a per-option basis. By
302 adding one of the declarations above, the <tt>--help</tt> option synopsis is now
306 USAGE: compiler [options] <b><input file></b>
309 -help - display available options (--help-hidden for more)
310 -o <filename> - Specify output filename
313 <p>... indicating that an input filename is expected.</p>
317 <!-- ======================================================================= -->
318 <div class="doc_subsection">
319 <a name="bool">Boolean Arguments</a>
322 <div class="doc_text">
324 <p>In addition to input and output filenames, we would like the compiler example
325 to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
326 file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
327 compatibility with some of our users. We can support these by declaring options
328 of boolean type like this:</p>
331 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
332 <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>"));
333 <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>);
336 <p>This does what you would expect: it declares three boolean variables
337 ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
338 options. Note that the "<tt>-q</tt>" option is specified with the "<a
339 href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
340 from being shown by the standard "<tt>--help</tt>" output (note that it is still
341 shown in the "<tt>--help-hidden</tt>" output).</p>
343 <p>The CommandLine library uses a <a href="#builtinparsers">different parser</a>
344 for different data types. For example, in the string case, the argument passed
345 to the option is copied literally into the content of the string variable... we
346 obviously cannot do that in the boolean case, however, so we must use a smarter
347 parser. In the case of the boolean parser, it allows no options (in which case
348 it assigns the value of true to the variable), or it allows the values
349 "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
350 following inputs:</p>
353 compiler -f # No value, 'Force' == true
354 compiler -f=true # Value specified, 'Force' == true
355 compiler -f=TRUE # Value specified, 'Force' == true
356 compiler -f=FALSE # Value specified, 'Force' == false
359 <p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns
360 the string values into boolean values, and rejects things like '<tt>compiler
361 -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
362 href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
363 like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
364 library calls to parse the string value into the specified data type.</p>
366 <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
369 USAGE: compiler [options] <input file>
372 <b>-f - Overwrite output files</b>
373 -o - Override output filename
374 <b>-quiet - Don't print informational messages</b>
375 -help - display available options (--help-hidden for more)
378 <p>and "<tt>opt --help-hidden</tt>" prints this:</p>
381 USAGE: compiler [options] <input file>
384 -f - Overwrite output files
385 -o - Override output filename
386 <b>-q - Don't print informational messages</b>
387 -quiet - Don't print informational messages
388 -help - display available options (--help-hidden for more)
391 <p>This brief example has shown you how to use the '<tt><a
392 href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
393 arguments. In addition to simple scalar arguments, the CommandLine library also
394 provides primitives to support CommandLine option <a href="#alias">aliases</a>,
395 and <a href="#list">lists</a> of options.</p>
399 <!-- ======================================================================= -->
400 <div class="doc_subsection">
401 <a name="alias">Argument Aliases</a>
404 <div class="doc_text">
406 <p>So far, the example works well, except for the fact that we need to check the
407 quiet condition like this now:</p>
411 if (!Quiet && !Quiet2) printInformationalMessage(...);
415 <p>... which is a real pain! Instead of defining two values for the same
416 condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
417 option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
421 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
422 <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>"));
423 <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));
426 <p>The third line (which is the only one we modified from above) defines a
427 "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by
428 the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
429 specified. Because aliases do not hold state, the only thing the program has to
430 query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
431 that they automatically hide themselves from the <tt>-help</tt> output
432 (although, again, they are still visible in the <tt>--help-hidden
435 <p>Now the application code can simply use:</p>
439 if (!Quiet) printInformationalMessage(...);
443 <p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>"
444 can be used to specify an alternative name for any variable type, and has many
449 <!-- ======================================================================= -->
450 <div class="doc_subsection">
451 <a name="onealternative">Selecting an alternative from a set of
455 <div class="doc_text">
457 <p>So far, we have seen how the CommandLine library handles builtin types like
458 <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
459 things it doesn't know about, like enums or '<tt>int*</tt>'s?</p>
461 <p>The answer is that it uses a table driven generic parser (unless you specify
462 your own parser, as described in the <a href="#extensionguide">Extension
463 Guide</a>). This parser maps literal strings to whatever type is required, and
464 requires you to tell it what this mapping should be.</p>
466 <p>Lets say that we would like to add four optimization levels to our
467 optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>",
468 "<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean
469 options like above, but there are several problems with this strategy:</p>
472 <li>A user could specify more than one of the options at a time, for example,
473 "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this
474 erroneous input for us.</li>
476 <li>We would have to test 4 different variables to see which ones are set.</li>
478 <li>This doesn't map to the numeric levels that we want... so we cannot easily
479 see if some level >= "<tt>-O1</tt>" is enabled.</li>
483 <p>To cope with these problems, we can use an enum value, and have the
484 CommandLine library fill it in with the appropriate level directly, which is
492 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
493 <a href="#cl::values">cl::values</a>(
494 clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
495 clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
496 clEnumVal(O2, "<i>Enable default optimizations</i>"),
497 clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
501 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
505 <p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
506 "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
507 that are listed in the declaration (Note that the declaration list must be
508 terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine
510 that the user can only specify one of the options, and it ensure that only valid
511 enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
512 command line arguments matched the enum values. With this option added, our
513 help output now is:</p>
516 USAGE: compiler [options] <input file>
519 <b>Choose optimization level:
520 -g - No optimizations, enable debugging
521 -O1 - Enable trivial optimizations
522 -O2 - Enable default optimizations
523 -O3 - Enable expensive optimizations</b>
524 -f - Overwrite output files
525 -help - display available options (--help-hidden for more)
526 -o <filename> - Specify output filename
527 -quiet - Don't print informational messages
530 <p>In this case, it is sort of awkward that flag names correspond directly to
531 enum names, because we probably don't want a enum definition named "<tt>g</tt>"
532 in our program. Because of this, we can alternatively write this example like
540 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
541 <a href="#cl::values">cl::values</a>(
542 clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
543 clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
544 clEnumVal(O2 , "<i>Enable default optimizations</i>"),
545 clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
549 if (OptimizationLevel == Debug) outputDebugInfo(...);
553 <p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we
554 can directly specify the name that the flag should get. In general a direct
555 mapping is nice, but sometimes you can't or don't want to preserve the mapping,
556 which is when you would use it.</p>
560 <!-- ======================================================================= -->
561 <div class="doc_subsection">
562 <a name="namedalternatives">Named Alternatives</a>
565 <div class="doc_text">
567 <p>Another useful argument form is a named alternative style. We shall use this
568 style in our compiler to specify different debug levels that can be used.
569 Instead of each debug level being its own switch, we want to support the
570 following options, of which only one can be specified at a time:
571 "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
572 "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
573 our optimization level flags, but we also specify an option name. For this
574 case, the code looks like this:</p>
578 nodebuginfo, quick, detailed
581 // Enable Debug Options to be specified on the command line
582 <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>"),
583 <a href="#cl::values">cl::values</a>(
584 clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
585 clEnumVal(quick, "<i>enable quick debug information</i>"),
586 clEnumVal(detailed, "<i>enable detailed debug information</i>"),
590 <p>This definition defines an enumerated command line variable of type "<tt>enum
591 DebugLev</tt>", which works exactly the same way as before. The difference here
592 is just the interface exposed to the user of your program and the help output by
593 the "<tt>--help</tt>" option:</p>
596 USAGE: compiler [options] <input file>
599 Choose optimization level:
600 -g - No optimizations, enable debugging
601 -O1 - Enable trivial optimizations
602 -O2 - Enable default optimizations
603 -O3 - Enable expensive optimizations
604 <b>-debug_level - Set the debugging level:
605 =none - disable debug information
606 =quick - enable quick debug information
607 =detailed - enable detailed debug information</b>
608 -f - Overwrite output files
609 -help - display available options (--help-hidden for more)
610 -o <filename> - Specify output filename
611 -quiet - Don't print informational messages
614 <p>Again, the only structural difference between the debug level declaration and
615 the optimiation level declaration is that the debug level declaration includes
616 an option name (<tt>"debug_level"</tt>), which automatically changes how the
617 library processes the argument. The CommandLine library supports both forms so
618 that you can choose the form most appropriate for your application.</p>
622 <!-- ======================================================================= -->
623 <div class="doc_subsection">
624 <a name="list">Parsing a list of options</a>
627 <div class="doc_text">
629 <p>Now that we have the standard run of the mill argument types out of the way,
630 lets get a little wild and crazy. Lets say that we want our optimizer to accept
631 a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
632 might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
633 this case, the order of the arguments and the number of appearances is very
634 important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
635 template is for. First, start by defining an enum of the optimizations that you
636 would like to perform:</p>
640 // 'inline' is a C++ keyword, so name it 'inlining'
641 dce, constprop, inlining, strip
645 <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
648 <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
649 <a href="#cl::values">cl::values</a>(
650 clEnumVal(dce , "<i>Dead Code Elimination</i>"),
651 clEnumVal(constprop , "<i>Constant Propagation</i>"),
652 clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
653 clEnumVal(strip , "<i>Strip Symbols</i>"),
657 <p>This defines a variable that is conceptually of the type
658 "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
662 for (unsigned i = 0; i != OptimizationList.size(); ++i)
663 switch (OptimizationList[i])
667 <p>... to iterate through the list of options specified.</p>
669 <p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is
670 completely general and may be used with any data types or other arguments that
671 you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One
672 especially useful way to use a list is to capture all of the positional
673 arguments together if there may be more than one specified. In the case of a
674 linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to
675 capture them into a list. This is naturally specified as:</p>
679 <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>);
683 <p>This variable works just like a "<tt>vector<string></tt>" object. As
684 such, accessing the list is simple, just like above. In this example, we used
685 the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
686 CommandLine library that it is an error if the user does not specify any
687 <tt>.o</tt> files on our command line. Again, this just reduces the amount of
688 checking we have to do.</p>
692 <!-- ======================================================================= -->
693 <div class="doc_subsection">
694 <a name="description">Adding freeform text to help output</a>
697 <div class="doc_text">
699 <p>As our program grows and becomes more mature, we may decide to put summary
700 information about what it does into the help output. The help output is styled
701 to look similar to a Unix <tt>man</tt> page, providing concise information about
702 a program. Unix <tt>man</tt> pages, however often have a description about what
703 the program does. To add this to your CommandLine program, simply pass a third
705 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
706 call in main. This additional argument is then printed as the overview
707 information for your program, allowing you to include any additional information
708 that you want. For example:</p>
711 int main(int argc, char **argv) {
712 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
713 " This program blah blah blah...\n");
718 <p>Would yield the help output:</p>
721 <b>OVERVIEW: CommandLine compiler example
723 This program blah blah blah...</b>
725 USAGE: compiler [options] <input file>
729 -help - display available options (--help-hidden for more)
730 -o <filename> - Specify output filename
736 <!-- *********************************************************************** -->
737 <div class="doc_section">
738 <a name="referenceguide">Reference Guide</a>
740 <!-- *********************************************************************** -->
742 <div class="doc_text">
744 <p>Now that you know the basics of how to use the CommandLine library, this
745 section will give you the detailed information you need to tune how command line
746 options work, as well as information on more "advanced" command line option
747 processing capabilities.</p>
751 <!-- ======================================================================= -->
752 <div class="doc_subsection">
753 <a name="positional">Positional Arguments</a>
756 <div class="doc_text">
758 <p>Positional arguments are those arguments that are not named, and are not
759 specified with a hyphen. Positional arguments should be used when an option is
760 specified by its position alone. For example, the standard Unix <tt>grep</tt>
761 tool takes a regular expression argument, and an optional filename to search
762 through (which defaults to standard input if a filename is not specified).
763 Using the CommandLine library, this would be specified as:</p>
766 <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>);
767 <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>"));
770 <p>Given these two option declarations, the <tt>--help</tt> output for our grep
771 replacement would look like this:</p>
774 USAGE: spiffygrep [options] <b><regular expression> <input file></b>
777 -help - display available options (--help-hidden for more)
780 <p>... and the resultant program could be used just like the standard
781 <tt>grep</tt> tool.</p>
783 <p>Positional arguments are sorted by their order of construction. This means
784 that command line options will be ordered according to how they are listed in a
785 .cpp file, but will not have an ordering defined if the positional arguments
786 are defined in multiple .cpp files. The fix for this problem is simply to
787 define all of your positional arguments in one .cpp file.</p>
792 <!-- _______________________________________________________________________ -->
793 <div class="doc_subsubsection">
794 <a name="--">Specifying positional options with hyphens</a>
797 <div class="doc_text">
799 <p>Sometimes you may want to specify a value to your positional argument that
800 starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
801 first, you will have trouble doing this, because it will try to find an argument
802 named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
803 Note that the system <tt>grep</tt> has the same problem:</p>
806 $ spiffygrep '-foo' test.txt
807 Unknown command line argument '-foo'. Try: spiffygrep --help'
809 $ grep '-foo' test.txt
810 grep: illegal option -- f
811 grep: illegal option -- o
812 grep: illegal option -- o
813 Usage: grep -hblcnsviw pattern file . . .
816 <p>The solution for this problem is the same for both your tool and the system
817 version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
818 the command line, it is telling the program that all options after the
819 '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
820 can use it like this:</p>
823 $ spiffygrep -- -foo test.txt
829 <!-- _______________________________________________________________________ -->
830 <div class="doc_subsubsection">
831 <a name="getPosition">Determining absolute position with getPosition()</a>
833 <div class="doc_text">
834 <p>Sometimes an option can affect or modify the meaning of another option. For
835 example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells
836 <tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force
837 the file to be interpreted as if it contained source code in language
838 <tt>LANG</tt>. In order to handle this properly , you need to know the
839 absolute position of each argument, especially those in lists, so their
840 interaction(s) can be applied correctly. This is also useful for options like
841 <tt>-llibname</tt> which is actually a positional argument that starts with
843 <p>So, generally, the problem is that you have two <tt>cl::list</tt> variables
844 that interact in some way. To ensure the correct interaction, you can use the
845 <tt>cl::list::getPosition(optnum)</tt> method. This method returns the
846 absolute position (as found on the command line) of the <tt>optnum</tt>
847 item in the <tt>cl::list</tt>.</p>
848 <p>The idiom for usage is like this:<pre><tt>
849 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
850 static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore);
852 int main(int argc, char**argv) {
854 std::vector<std::string>::iterator fileIt = Files.begin();
855 std::vector<std::string>::iterator libIt = Libraries.begin();
856 unsigned libPos = 0, filePos = 0;
858 if ( libIt != Libraries.end() )
859 libPos = Libraries.getPosition( libIt - Libraries.begin() );
862 if ( fileIt != Files.end() )
863 filePos = Files.getPosition( fileIt - Files.begin() );
867 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
868 // Source File Is next
871 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
876 break; // we're done with the list
880 <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an
881 <tt>unsigned getPosition()</tt> option that will provide the absolute position
882 of that option. You can apply the same approach as above with a
883 <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p>
886 <!-- _______________________________________________________________________ -->
887 <div class="doc_subsubsection">
888 <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
891 <div class="doc_text">
893 <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
894 used to construct programs that use "interpreter style" option processing. With
895 this style of option processing, all arguments specified after the last
896 positional argument are treated as special interpreter arguments that are not
897 interpreted by the command line argument.</p>
899 <p>As a concrete example, lets say we are developing a replacement for the
900 standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
901 you specify options to the shell itself (like <tt>-x</tt> which turns on trace
902 output), then you specify the name of the script to run, then you specify
903 arguments to the script. These arguments to the script are parsed by the bourne
904 shell command line option processor, but are not interpreted as options to the
905 shell itself. Using the CommandLine library, we would specify this as:</p>
908 <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>("-"));
909 <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>"));
910 <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
913 <p>which automatically provides the help output:</p>
916 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
919 -help - display available options (--help-hidden for more)
920 <b>-x - Enable trace output</b>
923 <p>At runtime, if we run our new shell replacement as '<tt>spiffysh -x test.sh
924 -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
925 <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
926 <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
927 were specified after the last positional argument (which is the script
930 <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
931 be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
932 per program, there must be at least one <a href="#positional">positional
933 argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
934 positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
935 href="#cl::list">cl::list</a> option.</p>
939 <!-- ======================================================================= -->
940 <div class="doc_subsection">
941 <a name="storage">Internal vs External Storage</a>
944 <div class="doc_text">
946 <p>By default, all command line options automatically hold the value that they
947 parse from the command line. This is very convenient in the common case,
948 especially when combined with the ability to define command line options in the
949 files that use them. This is called the internal storage model.</p>
951 <p>Sometimes, however, it is nice to separate the command line option processing
952 code from the storage of the value parsed. For example, lets say that we have a
953 '<tt>-debug</tt>' option that we would like to use to enable debug information
954 across the entire body of our program. In this case, the boolean value
955 controlling the debug code should be globally accessable (in a header file, for
956 example) yet the command line option processing code should not be exposed to
957 all of these clients (requiring lots of .cpp files to #include
958 <tt>CommandLine.h</tt>).</p>
960 <p>To do this, set up your .h file with your option, like this for example:</p>
963 <i>// DebugFlag.h - Get access to the '-debug' command line option
966 // DebugFlag - This boolean is set to true if the '-debug' command line option
967 // is specified. This should probably not be referenced directly, instead, use
968 // the DEBUG macro below.
970 extern bool DebugFlag;
972 <i>// DEBUG macro - This macro should be used by code to emit debug information.
973 // In the '-debug' option is specified on the command line, and if this is a
974 // debug build, then the code specified as the option to the macro will be
975 // executed. Otherwise it will not be. Example:
977 // DEBUG(cerr << "Bitset contains: " << Bitset << "\n");
979 <span class="doc_red">#ifdef NDEBUG
982 #define DEBUG(X)</span> \
983 do { if (DebugFlag) { X; } } while (0)
984 <span class="doc_red">#endif</span>
987 <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
988 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
989 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
990 an additial argument to our command line argument processor, and we specify
991 where to fill in with the <a href="#cl::location">cl::location</a>
995 bool DebugFlag; <i>// the actual value</i>
996 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
997 Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>,
998 <a href="#cl::location">cl::location</a>(DebugFlag));
1001 <p>In the above example, we specify "<tt>true</tt>" as the second argument to
1002 the <a href="#cl::opt">cl::opt</a> template, indicating that the template should
1003 not maintain a copy of the value itself. In addition to this, we specify the <a
1004 href="#cl::location">cl::location</a> attribute, so that <tt>DebugFlag</tt> is
1005 automatically set.</p>
1009 <!-- ======================================================================= -->
1010 <div class="doc_subsection">
1011 <a name="attributes">Option Attributes</a>
1014 <div class="doc_text">
1016 <p>This section describes the basic attributes that you can specify on
1021 <li>The option name attribute (which is required for all options, except <a
1022 href="#positional">positional options</a>) specifies what the option name is.
1023 This option is specified in simple double quotes:
1026 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
1031 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
1032 description for the option to be shown in the <tt>--help</tt> output for the
1035 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
1036 specifies a string that can be used to fine tune the <tt>--help</tt> output for
1037 a command line option. Look <a href="#value_desc_example">here</a> for an
1040 <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
1041 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
1042 not specified then the command line option value defaults to the value created
1043 by the default constructor for the type. <b>Warning</b>: If you specify both
1044 <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
1045 you must specify <b><tt>cl::location</tt></b> first, so that when the
1046 command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
1047 initial value. (You will get an error at runtime if you don't put them in
1048 the right order.)</li>
1050 <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
1051 store the value for a parsed command line option if using external storage. See
1052 the section on <a href="#storage">Internal vs External Storage</a> for more
1055 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
1056 specifies which option a <a href="#cl::alias">cl::alias</a> option is an alias
1059 <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
1060 the string-to-value mapping to be used by the generic parser. It takes a
1061 <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
1063 specify the option name, the value mapped to, and the description shown in the
1064 <tt>--help</tt> for the tool. Because the generic parser is used most
1065 frequently with enum values, two macros are often useful:
1069 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
1070 nice simple way to specify a triplet for an enum. This macro automatically
1071 makes the option name be the same as the enum name. The first option to the
1072 macro is the enum, the second is the description for the command line
1075 <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
1076 specify macro options where the option name doesn't equal the enum name. For
1077 this macro, the first argument is the enum value, the second is the flag name,
1078 and the second is the description.</li>
1082 You will get a compile time error if you try to use cl::values with a parser
1083 that does not support it.</li>
1089 <!-- ======================================================================= -->
1090 <div class="doc_subsection">
1091 <a name="modifiers">Option Modifiers</a>
1094 <div class="doc_text">
1096 <p>Option modifiers are the flags and expressions that you pass into the
1097 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1098 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
1099 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
1100 your application well.</p>
1102 <p>These options fall into five main catagories:</p>
1105 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
1106 <li><a href="#numoccurrences">Controlling the number of occurrences
1107 required and allowed</a></li>
1108 <li><a href="#valrequired">Controlling whether or not a value must be
1110 <li><a href="#formatting">Controlling other formatting options</a></li>
1111 <li><a href="#misc">Miscellaneous option modifiers</a></li>
1114 <p>It is not possible to specify two options from the same catagory (you'll get
1115 a runtime error) to a single option, except for options in the miscellaneous
1116 catagory. The CommandLine library specifies defaults for all of these settings
1117 that are the most useful in practice and the most common, which mean that you
1118 usually shouldn't have to worry about these.</p>
1122 <!-- _______________________________________________________________________ -->
1123 <div class="doc_subsubsection">
1124 <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
1127 <div class="doc_text">
1129 <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
1130 <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
1131 appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
1132 compiled program:</p>
1136 <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
1137 (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1138 href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
1139 in both help listings.</li>
1141 <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
1142 default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
1143 the option should not appear in the <tt>--help</tt> output, but should appear in
1144 the <tt>--help-hidden</tt> output.</li>
1146 <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
1147 indicates that the option should not appear in any help output.</li>
1153 <!-- _______________________________________________________________________ -->
1154 <div class="doc_subsubsection">
1155 <a name="numoccurrences">Controlling the number of occurrences required and
1159 <div class="doc_text">
1161 <p>This group of options is used to control how many time an option is allowed
1162 (or required) to be specified on the command line of your program. Specifying a
1163 value for this setting allows the CommandLine library to do error checking for
1166 <p>The allowed values for this option group are:</p>
1170 <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
1171 is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1172 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1173 allow either zero or one occurrence of the option to be specified.</li>
1175 <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
1176 (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
1177 indicates that your program will allow the option to be specified zero or more
1180 <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
1181 indicates that the specified option must be specified exactly one time.</li>
1183 <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
1184 indicates that the option must be specified at least one time.</li>
1186 <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1187 href="#positional">Positional arguments section</a></li>
1191 <p>If an option is not specified, then the value of the option is equal to the
1192 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1193 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1194 option value is initialized with the default constructor for the data type.</p>
1196 <p>If an option is specified multiple times for an option of the <tt><a
1197 href="#cl::opt">cl::opt</a></tt> class, only the last value will be
1202 <!-- _______________________________________________________________________ -->
1203 <div class="doc_subsubsection">
1204 <a name="valrequired">Controlling whether or not a value must be specified</a>
1207 <div class="doc_text">
1209 <p>This group of options is used to control whether or not the option allows a
1210 value to be present. In the case of the CommandLine library, a value is either
1211 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1212 string (e.g. '<tt>-o a.out</tt>').</p>
1214 <p>The allowed values for this option group are:</p>
1218 <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
1219 (which is the default for <tt>bool</tt> typed options) specifies that it is
1220 acceptable to have a value, or not. A boolean argument can be enabled just by
1221 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1222 If an option is specified with this mode, it is illegal for the value to be
1223 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1224 get this behavior, you must use the <a
1225 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
1227 <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
1228 (which is the default for all other types except for <a
1229 href="#onealternative">unnamed alternatives using the generic parser</a>)
1230 specifies that a value must be provided. This mode informs the command line
1231 library that if an option is not provides with an equal sign, that the next
1232 argument provided must be the value. This allows things like '<tt>-o
1233 a.out</tt>' to work.</li>
1235 <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
1236 modifier (which is the default for <a href="#onealternative">unnamed
1237 alternatives using the generic parser</a>) indicates that it is a runtime error
1238 for the user to specify a value. This can be provided to disallow users from
1239 providing options to boolean options (like '<tt>-foo=true</tt>').</li>
1243 <p>In general, the default values for this option group work just like you would
1244 want them to. As mentioned above, you can specify the <a
1245 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1246 argument to restrict your command line parser. These options are mostly useful
1247 when <a href="#extensionguide">extending the library</a>.</p>
1251 <!-- _______________________________________________________________________ -->
1252 <div class="doc_subsubsection">
1253 <a name="formatting">Controlling other formatting options</a>
1256 <div class="doc_text">
1258 <p>The formatting option group is used to specify that the command line option
1259 has special abilities and is otherwise different from other command line
1260 arguments. As usual, you can only specify at most one of these arguments.</p>
1264 <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
1265 modifier (which is the default all options) specifies that this option is
1268 <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
1269 specifies that this is a positional argument, that does not have a command line
1270 option associated with it. See the <a href="#positional">Positional
1271 Arguments</a> section for more information.</li>
1273 <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1274 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
1276 <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
1277 that this option prefixes its value. With 'Prefix' options, there is no equal
1278 sign that separates the value from the option name specified. This is useful
1279 for processing odd arguments like '<tt>-lmalloc -L/usr/lib'</tt> in a linker
1280 tool. Here, the '<tt>l</tt>' and '<tt>L</tt>' options are normal string (list)
1281 options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
1282 allow the CommandLine library to recognize them. Note that <a
1283 href="#cl::Prefix">cl::Prefix</a> options must not have the <a
1284 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li>
1286 <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
1287 to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
1288 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1289 command actually enables four different options, all of which are single
1290 letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
1295 <p>The CommandLine library does not restrict how you use the <a
1296 href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
1297 modifiers, but it is possible to specify ambiguous argument settings. Thus, it
1298 is possible to have multiple letter options that are prefix or grouping options,
1299 and they will still work as designed.</p>
1301 <p>To do this, the CommandLine library uses a greedy algorithm to parse the
1302 input option into (potentially multiple) prefix and grouping options. The
1303 strategy basically looks like this:</p>
1305 <p><tt>parse(string OrigInput) {</tt>
1308 <li><tt>string input = OrigInput;</tt>
1309 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1310 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1311 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1312 <li><tt>if (getOption(input).isPrefix())<br>
1313 return getOption(input).parse(input);</tt>
1314 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1315 getOption(input).parse();<br>
1316 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1317 input = OrigInput;<br>
1318 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1320 <li><tt>if (!OrigInput.empty()) error();</tt></li>
1328 <!-- _______________________________________________________________________ -->
1329 <div class="doc_subsubsection">
1330 <a name="misc">Miscellaneous option modifiers</a>
1333 <div class="doc_text">
1335 <p>The miscellaneous option modifiers are the only flags where you can specify
1336 more than one flag from the set: they are not mutually exclusive. These flags
1337 specify boolean properties that modify the option.</p>
1341 <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
1342 indicates that any commas specified for an option's value should be used to
1343 split the value up into multiple values for the option. For example, these two
1344 options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
1345 "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
1346 makes sense to be used in a case where the option is allowed to accept one or
1347 more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
1349 <li><a name="cl::PositionalEatsArgs">The
1350 <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
1351 positional arguments, and only makes sense for lists) indicates that positional
1352 argument should consume any strings after it (including strings that start with
1353 a "-") up until another recognized positional argument. For example, if you
1354 have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the
1355 string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
1356 -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
1357 "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
1361 <p>So far, these are the only two miscellaneous option modifiers.</p>
1365 <!-- ======================================================================= -->
1366 <div class="doc_subsection">
1367 <a name="toplevel">Top-Level Classes and Functions</a>
1370 <div class="doc_text">
1372 <p>Despite all of the built-in flexibility, the CommandLine option library
1373 really only consists of one function (<a
1374 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1375 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1376 href="#cl::list"><tt>cl::list</tt></a>, and <a
1377 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1378 classes in detail.</p>
1382 <!-- _______________________________________________________________________ -->
1383 <div class="doc_subsubsection">
1384 <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
1388 <div class="doc_text">
1390 <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1391 directly from <tt>main</tt>, and is used to fill in the values of all of the
1392 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1395 <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1396 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1397 which holds <a href="#description">additional extra text</a> to emit when the
1398 <tt>--help</tt> option is invoked.</p>
1402 <!-- _______________________________________________________________________ -->
1403 <div class="doc_subsubsection">
1404 <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
1408 <div class="doc_text">
1410 <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
1412 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
1413 except that it is designed to take values for options from an environment
1414 variable, for those cases in which reading the command line is not convenient or
1415 not desired. It fills in the values of all the command line option variables
1417 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
1420 <p>It takes three parameters: first, the name of the program (since
1421 <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
1422 second, the name of the environment variable to examine, and third, the optional
1423 <a href="#description">additional extra text</a> to emit when the
1424 <tt>--help</tt> option is invoked.</p>
1426 <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
1427 variable's value up into words and then process them using
1428 <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
1429 <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
1430 quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
1431 be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
1432 which is different from what you would get from the shell with the same
1437 <!-- _______________________________________________________________________ -->
1438 <div class="doc_subsubsection">
1439 <a name="cl::opt">The <tt>cl::opt</tt> class</a>
1442 <div class="doc_text">
1444 <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
1445 options, and is the one used most of the time. It is a templated class which
1446 can take up to three arguments (all except for the first have default values
1450 <b>namespace</b> cl {
1451 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1452 <b>class</b> ParserClass = parser<DataType> >
1457 <p>The first template argument specifies what underlying data type the command
1458 line argument is, and is used to select a default parser implementation. The
1459 second template argument is used to specify whether the option should contain
1460 the storage for the option (the default) or whether external storage should be
1461 used to contain the value parsed for the option (see <a href="#storage">Internal
1462 vs External Storage</a> for more information).</p>
1464 <p>The third template argument specifies which parser to use. The default value
1465 selects an instantiation of the <tt>parser</tt> class based on the underlying
1466 data type of the option. In general, this default works well for most
1467 applications, so this option is only used when using a <a
1468 href="#customparser">custom parser</a>.</p>
1472 <!-- _______________________________________________________________________ -->
1473 <div class="doc_subsubsection">
1474 <a name="cl::list">The <tt>cl::list</tt> class</a>
1477 <div class="doc_text">
1479 <p>The <tt>cl::list</tt> class is the class used to represent a list of command
1480 line options. It too is a templated class which can take up to three
1484 <b>namespace</b> cl {
1485 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1486 <b>class</b> ParserClass = parser<DataType> >
1491 <p>This class works the exact same as the <a
1492 href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
1493 the <b>type</b> of the external storage, not a boolean value. For this class,
1494 the marker type '<tt>bool</tt>' is used to indicate that internal storage should
1499 <!-- _______________________________________________________________________ -->
1500 <div class="doc_subsubsection">
1501 <a name="cl::alias">The <tt>cl::alias</tt> class</a>
1504 <div class="doc_text">
1506 <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1507 aliases for other arguments.</p>
1510 <b>namespace</b> cl {
1515 <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
1516 used to specify which option this is an alias for. Alias arguments default to
1517 being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
1518 the conversion from string to data.</p>
1522 <!-- ======================================================================= -->
1523 <div class="doc_subsection">
1524 <a name="builtinparsers">Builtin parsers</a>
1527 <div class="doc_text">
1529 <p>Parsers control how the string value taken from the command line is
1530 translated into a typed value, suitable for use in a C++ program. By default,
1531 the CommandLine library uses an instance of <tt>parser<type></tt> if the
1532 command line option specifies that it uses values of type '<tt>type</tt>'.
1533 Because of this, custom option processing is specified with specializations of
1534 the '<tt>parser</tt>' class.</p>
1536 <p>The CommandLine library provides the following builtin parser
1537 specializations, which are sufficient for most applications. It can, however,
1538 also be extended to work with new data types and new ways of interpreting the
1539 same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
1540 details on this type of library extension.</p>
1544 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
1545 can be used to map strings values to any data type, through the use of the <a
1546 href="#cl::values">cl::values</a> property, which specifies the mapping
1547 information. The most common use of this parser is for parsing enum values,
1548 which allows you to use the CommandLine library for all of the error checking to
1549 make sure that only valid enum values are specified (as opposed to accepting
1550 arbitrary strings). Despite this, however, the generic parser class can be used
1551 for any data type.</li>
1553 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
1554 is used to convert boolean strings to a boolean value. Currently accepted
1555 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1556 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
1558 <li><a name="stringparser">The <b><tt>parser<string></tt>
1559 specialization</b></a> simply stores the parsed string into the string value
1560 specified. No conversion or modification of the data is performed.</li>
1562 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
1563 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1564 accept a decimal number (with an optional '+' or '-' prefix) which must start
1565 with a non-zero digit. It accepts octal numbers, which are identified with a
1566 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1567 '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
1569 <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
1570 <b><tt>parser<float></tt> specializations</b> use the standard C
1571 <tt>strtod</tt> function to convert floating point strings into floating point
1572 values. As such, a broad range of string formats is supported, including
1573 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1580 <!-- *********************************************************************** -->
1581 <div class="doc_section">
1582 <a name="extensionguide">Extension Guide</a>
1584 <!-- *********************************************************************** -->
1586 <div class="doc_text">
1588 <p>Although the CommandLine library has a lot of functionality built into it
1589 already (as discussed previously), one of its true strengths lie in its
1590 extensibility. This section discusses how the CommandLine library works under
1591 the covers and illustrates how to do some simple, common, extensions.</p>
1595 <!-- ======================================================================= -->
1596 <div class="doc_subsection">
1597 <a name="customparser">Writing a custom parser</a>
1600 <div class="doc_text">
1602 <p>One of the simplest and most common extensions is the use of a custom parser.
1603 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1604 of the CommandLine library that turns string input from the user into a
1605 particular parsed data type, validating the input in the process.</p>
1607 <p>There are two ways to use a new parser:</p>
1613 <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1614 your custom data type.<p>
1616 <p>This approach has the advantage that users of your custom data type will
1617 automatically use your custom parser whenever they define an option with a value
1618 type of your data type. The disadvantage of this approach is that it doesn't
1619 work if your fundemental data type is something that is already supported.</p>
1625 <p>Write an independent class, using it explicitly from options that need
1628 <p>This approach works well in situations where you would line to parse an
1629 option using special syntax for a not-very-special data-type. The drawback of
1630 this approach is that users of your parser have to be aware that they are using
1631 your parser, instead of the builtin ones.</p>
1637 <p>To guide the discussion, we will discuss a custom parser that accepts file
1638 sizes, specified with an optional unit after the numeric size. For example, we
1639 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1640 this case, the underlying data type we want to parse into is
1641 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1642 this the default for all <tt>unsigned</tt> options.</p>
1644 <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
1647 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1648 <i>// parse - Return true on error.</i>
1649 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1650 <b>unsigned</b> &Val);
1654 <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
1655 fill in the default, boiler plate, code for us. We give it the data type that
1656 we parse into (the last argument to the <tt>parse</tt> method so that clients of
1657 our custom parser know what object type to pass in to the parse method (here we
1658 declare that we parse into '<tt>unsigned</tt>' variables.</p>
1660 <p>For most purposes, the only method that must be implemented in a custom
1661 parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
1662 whenever the option is invoked, passing in the option itself, the option name,
1663 the string to parse, and a reference to a return value. If the string to parse
1664 is not well formed, the parser should output an error message and return true.
1665 Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
1666 our example, we implement <tt>parse</tt> as:</p>
1669 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1670 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1671 <b>const char</b> *ArgStart = Arg.c_str();
1674 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1675 Val = (unsigned)strtol(ArgStart, &End, 0);
1678 <b>switch</b> (*End++) {
1679 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1680 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1681 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1684 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1685 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1686 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1689 <i>// Print an error message if unrecognized character!</i>
1690 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1696 <p>This function implements a very simple parser for the kinds of strings we are
1697 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1698 example), it is good enough for this example. Note that we use the option
1699 itself to print out the error message (the <tt>error</tt> method always returns
1700 true) in order to get a nice error message (shown below). Now that we have our
1701 parser class, we can use it like this:</p>
1704 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1705 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1706 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1709 <p>Which adds this to the output of our program:</p>
1713 -help - display available options (--help-hidden for more)
1715 <b>-max-file-size=<size> - Maximum file size to accept</b>
1718 <p>And we can test that our parse works correctly now (the test program just
1719 prints out the max-file-size argument value):</p>
1724 $ ./test -max-file-size=123MB
1726 $ ./test -max-file-size=3G
1728 $ ./test -max-file-size=dog
1729 -max-file-size option: 'dog' value invalid for file size argument!
1732 <p>It looks like it works. The error message that we get is nice and helpful,
1733 and we seem to accept reasonable file sizes. This wraps up the "custom parser"
1738 <!-- ======================================================================= -->
1739 <div class="doc_subsection">
1740 <a name="explotingexternal">Exploiting external storage</a>
1743 <div class="doc_text">
1744 <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that
1745 will automatically be included in any program that links with that library.
1746 This is a feature. However, sometimes it is necessary to know the value of the
1747 command line option outside of the library. In these cases the library does or
1748 should provide an external storage location that is accessible to users of the
1749 library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the
1750 <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt>
1751 flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p>
1753 <p>TODO: complete this section</p>
1757 <!-- ======================================================================= -->
1758 <div class="doc_subsection">
1759 <a name="dynamicopts">Dynamically adding command line options</a>
1762 <div class="doc_text">
1764 <p>TODO: fill in this section</p>
1768 <!-- *********************************************************************** -->
1772 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1773 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1774 <a href="http://validator.w3.org/check/referer"><img
1775 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
1777 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1778 <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
1779 Last modified: $Date$