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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="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
37 <li><a href="#storage">Internal vs External Storage</a></li>
39 <li><a href="#attributes">Option Attributes</a></li>
41 <li><a href="#modifiers">Option Modifiers</a>
43 <li><a href="#hiding">Hiding an option from <tt>--help</tt>
45 <li><a href="#numoccurrences">Controlling the number of occurrences
46 required and allowed</a></li>
47 <li><a href="#valrequired">Controlling whether or not a value must be
49 <li><a href="#formatting">Controlling other formatting options</a></li>
50 <li><a href="#misc">Miscellaneous option modifiers</a></li>
53 <li><a href="#toplevel">Top-Level Classes and Functions</a>
55 <li><a href="#cl::ParseCommandLineOptions">The
56 <tt>cl::ParseCommandLineOptions</tt> function</a></li>
57 <li><a href="#cl::ParseEnvironmentOptions">The
58 <tt>cl::ParseEnvironmentOptions</tt> function</a></li>
59 <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li>
60 <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li>
61 <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li>
64 <li><a href="#builtinparsers">Builtin parsers</a>
66 <li><a href="#genericparser">The Generic <tt>parser<t></tt>
68 <li><a href="#boolparser">The <tt>parser<bool></tt>
69 specialization</a></li>
70 <li><a href="#stringparser">The <tt>parser<string></tt>
71 specialization</a></li>
72 <li><a href="#intparser">The <tt>parser<int></tt>
73 specialization</a></li>
74 <li><a href="#doubleparser">The <tt>parser<double></tt> and
75 <tt>parser<float></tt> specializations</a></li>
78 <li><a href="#extensionguide">Extension Guide</a>
80 <li><a href="#customparser">Writing a custom parser</a></li>
81 <li><a href="#explotingexternal">Exploiting external storage</a></li>
82 <li><a href="#dynamicopts">Dynamically adding command line
87 <div class="doc_author">
88 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
91 <!-- *********************************************************************** -->
92 <div class="doc_section">
93 <a name="introduction">Introduction</a>
95 <!-- *********************************************************************** -->
97 <div class="doc_text">
99 <p>This document describes the CommandLine argument processing library. It will
100 show you how to use it, and what it can do. The CommandLine library uses a
101 declarative approach to specifying the command line options that your program
102 takes. By default, these options declarations implicitly hold the value parsed
103 for the option declared (of course this <a href="#storage">can be
106 <p>Although there are a <b>lot</b> of command line argument parsing libraries
107 out there in many different languages, none of them fit well with what I needed.
108 By looking at the features and problems of other libraries, I designed the
109 CommandLine library to have the following features:</p>
112 <li>Speed: The CommandLine library is very quick and uses little resources. The
113 parsing time of the library is directly proportional to the number of arguments
114 parsed, not the the number of options recognized. Additionally, command line
115 argument values are captured transparently into user defined global variables,
116 which can be accessed like any other variable (and with the same
119 <li>Type Safe: As a user of CommandLine, you don't have to worry about
120 remembering the type of arguments that you want (is it an int? a string? a
121 bool? an enum?) and keep casting it around. Not only does this help prevent
122 error prone constructs, it also leads to dramatically cleaner source code.</li>
124 <li>No subclasses required: To use CommandLine, you instantiate variables that
125 correspond to the arguments that you would like to capture, you don't subclass a
126 parser. This means that you don't have to write <b>any</b> boilerplate
129 <li>Globally accessible: Libraries can specify command line arguments that are
130 automatically enabled in any tool that links to the library. This is possible
131 because the application doesn't have to keep a "list" of arguments to pass to
132 the parser. This also makes supporting <a href="#dynamicopts">dynamically
133 loaded options</a> trivial.</li>
135 <li>Cleaner: CommandLine supports enum and other types directly, meaning that
136 there is less error and more security built into the library. You don't have to
137 worry about whether your integral command line argument accidentally got
138 assigned a value that is not valid for your enum type.</li>
140 <li>Powerful: The CommandLine library supports many different types of
141 arguments, from simple <a href="#boolparser">boolean flags</a> to <a
142 href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
143 href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
144 href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
145 arguments</a>. This is possible because CommandLine is...</li>
147 <li>Extensible: It is very simple to add a new argument type to CommandLine.
148 Simply specify the parser that you want to use with the command line option when
149 you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li>
151 <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
152 that you, the user, have to do. For example, it automatically provides a
153 <tt>--help</tt> option that shows the available command line options for your
154 tool. Additionally, it does most of the basic correctness checking for
157 <li>Capable: The CommandLine library can handle lots of different forms of
158 options often found in real programs. For example, <a
159 href="#positional">positional</a> arguments, <tt>ls</tt> style <a
160 href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
161 -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
162 options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
163 href="#cl::ConsumeAfter">interpreter style options</a>.</li>
167 <p>This document will hopefully let you jump in and start using CommandLine in
168 your utility quickly and painlessly. Additionally it should be a simple
169 reference manual to figure out how stuff works. If it is failing in some area
170 (or you want an extension to the library), nag the author, <a
171 href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
175 <!-- *********************************************************************** -->
176 <div class="doc_section">
177 <a name="quickstart">Quick Start Guide</a>
179 <!-- *********************************************************************** -->
181 <div class="doc_text">
183 <p>This section of the manual runs through a simple CommandLine'ification of a
184 basic compiler tool. This is intended to show you how to jump into using the
185 CommandLine library in your own program, and show you some of the cool things it
188 <p>To start out, you need to include the CommandLine header file into your
192 #include "Support/CommandLine.h"
195 <p>Additionally, you need to add this as the first line of your main
199 int main(int argc, char **argv) {
200 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
205 <p>... which actually parses the arguments and fills in the variable
208 <p>Now that you are ready to support command line arguments, we need to tell the
209 system which ones we want, and what type of argument they are. The CommandLine
210 library uses a declarative syntax to model command line arguments with the
211 global variable declarations that capture the parsed values. This means that
212 for every command line option that you would like to support, there should be a
213 global variable declaration to capture the result. For example, in a compiler,
214 we would like to support the unix standard '<tt>-o <filename></tt>' option
215 to specify where to put the output. With the CommandLine library, this is
216 represented like this:</p>
218 <a name="value_desc_example"></a>
220 <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>"));
223 <p>This declares a global variable "<tt>OutputFilename</tt>" that is used to
224 capture the result of the "<tt>o</tt>" argument (first parameter). We specify
225 that this is a simple scalar option by using the "<tt><a
226 href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a
227 href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library
228 that the data type that we are parsing is a string.</p>
230 <p>The second and third parameters (which are optional) are used to specify what
231 to output for the "<tt>--help</tt>" option. In this case, we get a line that
235 USAGE: compiler [options]
238 -help - display available options (--help-hidden for more)
239 <b>-o <filename> - Specify output filename</b>
242 <p>Because we specified that the command line option should parse using the
243 <tt>string</tt> data type, the variable declared is automatically usable as a
244 real string in all contexts that a normal C++ string object may be used. For
249 ofstream Output(OutputFilename.c_str());
254 <p>There are many different options that you can use to customize the command
255 line option handling library, but the above example shows the general interface
256 to these options. The options can be specified in any order, and are specified
257 with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
258 there are no positional dependencies to remember. The available options are
259 discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p>
261 <p>Continuing the example, we would like to have our compiler take an input
262 filename as well as an output filename, but we do not want the input filename to
263 be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
264 style of argument, the CommandLine library allows for <a
265 href="#positional">positional</a> arguments to be specified for the program.
266 These positional arguments are filled with command line parameters that are not
267 in option form. We use this feature like this:</p>
270 <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>"));
273 <p>This declaration indicates that the first positional argument should be
274 treated as the input filename. Here we use the <tt><a
275 href="#cl::init">cl::init</a></tt> option to specify an initial value for the
276 command line option, which is used if the option is not specified (if you do not
277 specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
278 the default constructor for the data type is used to initialize the value).
279 Command line options default to being optional, so if we would like to require
280 that the user always specify an input filename, we would add the <tt><a
281 href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
282 <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p>
285 <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>);
288 <p>Again, the CommandLine library does not require the options to be specified
289 in any particular order, so the above declaration is equivalent to:</p>
292 <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>"));
295 <p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag,
296 the CommandLine library will automatically issue an error if the argument is not
297 specified, which shifts all of the command line option verification code out of
298 your application into the library. This is just one example of how using flags
299 can alter the default behaviour of the library, on a per-option basis. By
300 adding one of the declarations above, the <tt>--help</tt> option synopsis is now
304 USAGE: compiler [options] <b><input file></b>
307 -help - display available options (--help-hidden for more)
308 -o <filename> - Specify output filename
311 <p>... indicating that an input filename is expected.</p>
315 <!-- ======================================================================= -->
316 <div class="doc_subsection">
317 <a name="bool">Boolean Arguments</a>
320 <div class="doc_text">
322 <p>In addition to input and output filenames, we would like the compiler example
323 to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
324 file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
325 compatibility with some of our users. We can support these by declaring options
326 of boolean type like this:</p>
329 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
330 <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>"));
331 <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>);
334 <p>This does what you would expect: it declares three boolean variables
335 ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
336 options. Note that the "<tt>-q</tt>" option is specified with the "<a
337 href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
338 from being shown by the standard "<tt>--help</tt>" output (note that it is still
339 shown in the "<tt>--help-hidden</tt>" output).</p>
341 <p>The CommandLine library uses a <a href="#builtinparsers">different parser</a>
342 for different data types. For example, in the string case, the argument passed
343 to the option is copied literally into the content of the string variable... we
344 obviously cannot do that in the boolean case, however, so we must use a smarter
345 parser. In the case of the boolean parser, it allows no options (in which case
346 it assigns the value of true to the variable), or it allows the values
347 "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
348 following inputs:</p>
351 compiler -f # No value, 'Force' == true
352 compiler -f=true # Value specified, 'Force' == true
353 compiler -f=TRUE # Value specified, 'Force' == true
354 compiler -f=FALSE # Value specified, 'Force' == false
357 <p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns
358 the string values into boolean values, and rejects things like '<tt>compiler
359 -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
360 href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
361 like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
362 library calls to parse the string value into the specified data type.</p>
364 <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
367 USAGE: compiler [options] <input file>
370 <b>-f - Overwrite output files</b>
371 -o - Override output filename
372 <b>-quiet - Don't print informational messages</b>
373 -help - display available options (--help-hidden for more)
376 <p>and "<tt>opt --help-hidden</tt>" prints this:</p>
379 USAGE: compiler [options] <input file>
382 -f - Overwrite output files
383 -o - Override output filename
384 <b>-q - Don't print informational messages</b>
385 -quiet - Don't print informational messages
386 -help - display available options (--help-hidden for more)
389 <p>This brief example has shown you how to use the '<tt><a
390 href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
391 arguments. In addition to simple scalar arguments, the CommandLine library also
392 provides primitives to support CommandLine option <a href="#alias">aliases</a>,
393 and <a href="#list">lists</a> of options.</p>
397 <!-- ======================================================================= -->
398 <div class="doc_subsection">
399 <a name="alias">Argument Aliases</a>
402 <div class="doc_text">
404 <p>So far, the example works well, except for the fact that we need to check the
405 quiet condition like this now:</p>
409 if (!Quiet && !Quiet2) printInformationalMessage(...);
413 <p>... which is a real pain! Instead of defining two values for the same
414 condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
415 option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
419 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
420 <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>"));
421 <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));
424 <p>The third line (which is the only one we modified from above) defines a
425 "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by
426 the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
427 specified. Because aliases do not hold state, the only thing the program has to
428 query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
429 that they automatically hide themselves from the <tt>-help</tt> output
430 (although, again, they are still visible in the <tt>--help-hidden
433 <p>Now the application code can simply use:</p>
437 if (!Quiet) printInformationalMessage(...);
441 <p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>"
442 can be used to specify an alternative name for any variable type, and has many
447 <!-- ======================================================================= -->
448 <div class="doc_subsection">
449 <a name="onealternative">Selecting an alternative from a set of
453 <div class="doc_text">
455 <p>So far, we have seen how the CommandLine library handles builtin types like
456 <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
457 things it doesn't know about, like enums or '<tt>int*</tt>'s?</p>
459 <p>The answer is that it uses a table driven generic parser (unless you specify
460 your own parser, as described in the <a href="#extensionguide">Extension
461 Guide</a>). This parser maps literal strings to whatever type is required, are
462 requires you to tell it what this mapping should be.</p>
464 <p>Lets say that we would like to add four optimizations levels to our
465 optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>",
466 "<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean
467 options like above, but there are several problems with this strategy:</p>
470 <li>A user could specify more than one of the options at a time, for example,
471 "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this
472 erroneous input for us.</li>
474 <li>We would have to test 4 different variables to see which ones are set.</li>
476 <li>This doesn't map to the numeric levels that we want... so we cannot easily
477 see if some level >= "<tt>-O1</tt>" is enabled.</li>
481 <p>To cope with these problems, we can use an enum value, and have the
482 CommandLine library fill it in with the appropriate level directly, which is
490 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
491 <a href="#cl::values">cl::values</a>(
492 clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
493 clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
494 clEnumVal(O2, "<i>Enable default optimizations</i>"),
495 clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
499 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
503 <p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
504 "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
505 that are listed in the declaration (Note that the declaration list must be
506 terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine
508 that the user can only specify one of the options, and it ensure that only valid
509 enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
510 command line arguments matched the enum values. With this option added, our
511 help output now is:</p>
514 USAGE: compiler [options] <input file>
517 <b>Choose optimization level:
518 -g - No optimizations, enable debugging
519 -O1 - Enable trivial optimizations
520 -O2 - Enable default optimizations
521 -O3 - Enable expensive optimizations</b>
522 -f - Overwrite output files
523 -help - display available options (--help-hidden for more)
524 -o <filename> - Specify output filename
525 -quiet - Don't print informational messages
528 <p>In this case, it is sort of awkward that flag names correspond directly to
529 enum names, because we probably don't want a enum definition named "<tt>g</tt>"
530 in our program. Because of this, we can alternatively write this example like
538 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
539 <a href="#cl::values">cl::values</a>(
540 clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
541 clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
542 clEnumVal(O2 , "<i>Enable default optimizations</i>"),
543 clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
547 if (OptimizationLevel == Debug) outputDebugInfo(...);
551 <p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we
552 can directly specify the name that the flag should get. In general a direct
553 mapping is nice, but sometimes you can't or don't want to preserve the mapping,
554 which is when you would use it.</p>
558 <!-- ======================================================================= -->
559 <div class="doc_subsection">
560 <a name="namedalternatives">Named Alternatives</a>
563 <div class="doc_text">
565 <p>Another useful argument form is a named alternative style. We shall use this
566 style in our compiler to specify different debug levels that can be used.
567 Instead of each debug level being its own switch, we want to support the
568 following options, of which only one can be specified at a time:
569 "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
570 "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
571 our optimization level flags, but we also specify an option name. For this
572 case, the code looks like this:</p>
576 nodebuginfo, quick, detailed
579 // Enable Debug Options to be specified on the command line
580 <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>"),
581 <a href="#cl::values">cl::values</a>(
582 clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
583 clEnumVal(quick, "<i>enable quick debug information</i>"),
584 clEnumVal(detailed, "<i>enable detailed debug information</i>"),
588 <p>This definition defines an enumerated command line variable of type "<tt>enum
589 DebugLev</tt>", which works exactly the same way as before. The difference here
590 is just the interface exposed to the user of your program and the help output by
591 the "<tt>--help</tt>" option:</p>
594 USAGE: compiler [options] <input file>
597 Choose optimization level:
598 -g - No optimizations, enable debugging
599 -O1 - Enable trivial optimizations
600 -O2 - Enable default optimizations
601 -O3 - Enable expensive optimizations
602 <b>-debug_level - Set the debugging level:
603 =none - disable debug information
604 =quick - enable quick debug information
605 =detailed - enable detailed debug information</b>
606 -f - Overwrite output files
607 -help - display available options (--help-hidden for more)
608 -o <filename> - Specify output filename
609 -quiet - Don't print informational messages
612 <p>Again, the only structural difference between the debug level declaration and
613 the optimiation level declaration is that the debug level declaration includes
614 an option name (<tt>"debug_level"</tt>), which automatically changes how the
615 library processes the argument. The CommandLine library supports both forms so
616 that you can choose the form most appropriate for your application.</p>
620 <!-- ======================================================================= -->
621 <div class="doc_subsection">
622 <a name="list">Parsing a list of options</a>
625 <div class="doc_text">
627 <p>Now that we have the standard run of the mill argument types out of the way,
628 lets get a little wild and crazy. Lets say that we want our optimizer to accept
629 a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
630 might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
631 this case, the order of the arguments and the number of appearances is very
632 important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
633 template is for. First, start by defining an enum of the optimizations that you
634 would like to perform:</p>
638 // 'inline' is a C++ keyword, so name it 'inlining'
639 dce, constprop, inlining, strip
643 <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
646 <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
647 <a href="#cl::values">cl::values</a>(
648 clEnumVal(dce , "<i>Dead Code Elimination</i>"),
649 clEnumVal(constprop , "<i>Constant Propagation</i>"),
650 clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
651 clEnumVal(strip , "<i>Strip Symbols</i>"),
655 <p>This defines a variable that is conceptually of the type
656 "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
660 for (unsigned i = 0; i != OptimizationList.size(); ++i)
661 switch (OptimizationList[i])
665 <p>... to iterate through the list of options specified.</p>
667 <p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is
668 completely general and may be used with any data types or other arguments that
669 you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One
670 especially useful way to use a list is to capture all of the positional
671 arguments together if there may be more than one specified. In the case of a
672 linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to
673 capture them into a list. This is naturally specified as:</p>
677 <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>);
681 <p>This variable works just like a "<tt>vector<string></tt>" object. As
682 such, accessing the list is simple, just like above. In this example, we used
683 the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
684 CommandLine library that it is an error if the user does not specify any
685 <tt>.o</tt> files on our command line. Again, this just reduces the amount of
686 checking we have to do.</p>
690 <!-- ======================================================================= -->
691 <div class="doc_subsection">
692 <a name="description">Adding freeform text to help output</a>
695 <div class="doc_text">
697 <p>As our program grows and becomes more mature, we may decide to put summary
698 information about what it does into the help output. The help output is styled
699 to look similar to a Unix <tt>man</tt> page, providing concise information about
700 a program. Unix <tt>man</tt> pages, however often have a description about what
701 the program does. To add this to your CommandLine program, simply pass a third
703 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
704 call in main. This additional argument is then printed as the overview
705 information for your program, allowing you to include any additional information
706 that you want. For example:</p>
709 int main(int argc, char **argv) {
710 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
711 " This program blah blah blah...\n");
716 <p>Would yield the help output:</p>
719 <b>OVERVIEW: CommandLine compiler example
721 This program blah blah blah...</b>
723 USAGE: compiler [options] <input file>
727 -help - display available options (--help-hidden for more)
728 -o <filename> - Specify output filename
734 <!-- *********************************************************************** -->
735 <div class="doc_section">
736 <a name="referenceguide">Reference Guide</a>
738 <!-- *********************************************************************** -->
740 <div class="doc_text">
742 <p>Now that you know the basics of how to use the CommandLine library, this
743 section will give you the detailed information you need to tune how command line
744 options work, as well as information on more "advanced" command line option
745 processing capabilities.</p>
749 <!-- ======================================================================= -->
750 <div class="doc_subsection">
751 <a name="positional">Positional Arguments</a>
754 <div class="doc_text">
756 <p>Positional arguments are those arguments that are not named, and are not
757 specified with a hyphen. Positional arguments should be used when an option is
758 specified by its position alone. For example, the standard Unix <tt>grep</tt>
759 tool takes a regular expression argument, and an optional filename to search
760 through (which defaults to standard input if a filename is not specified).
761 Using the CommandLine library, this would be specified as:</p>
764 <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>);
765 <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>"));
768 <p>Given these two option declarations, the <tt>--help</tt> output for our grep
769 replacement would look like this:</p>
772 USAGE: spiffygrep [options] <b><regular expression> <input file></b>
775 -help - display available options (--help-hidden for more)
778 <p>... and the resultant program could be used just like the standard
779 <tt>grep</tt> tool.</p>
781 <p>Positional arguments are sorted by their order of construction. This means
782 that command line options will be ordered according to how they are listed in a
783 .cpp file, but will not have an ordering defined if they positional arguments
784 are defined in multiple .cpp files. The fix for this problem is simply to
785 define all of your positional arguments in one .cpp file.</p>
790 <!-- _______________________________________________________________________ -->
791 <div class="doc_subsubsection">
792 <a name="--">Specifying positional options with hyphens</a>
795 <div class="doc_text">
797 <p>Sometimes you may want to specify a value to your positional argument that
798 starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
799 first, you will have trouble doing this, because it will try to find an argument
800 named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
801 Note that the system <tt>grep</tt> has the same problem:</p>
804 $ spiffygrep '-foo' test.txt
805 Unknown command line argument '-foo'. Try: spiffygrep --help'
807 $ grep '-foo' test.txt
808 grep: illegal option -- f
809 grep: illegal option -- o
810 grep: illegal option -- o
811 Usage: grep -hblcnsviw pattern file . . .
814 <p>The solution for this problem is the same for both your tool and the system
815 version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
816 the command line, it is telling the program that all options after the
817 '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
818 can use it like this:</p>
821 $ spiffygrep -- -foo test.txt
827 <!-- _______________________________________________________________________ -->
828 <div class="doc_subsubsection">
829 <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
832 <div class="doc_text">
834 <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
835 used to construct programs that use "interpreter style" option processing. With
836 this style of option processing, all arguments specified after the last
837 positional argument are treated as special interpreter arguments that are not
838 interpreted by the command line argument.</p>
840 <p>As a concrete example, lets say we are developing a replacement for the
841 standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
842 you specify options to the shell itself (like <tt>-x</tt> which turns on trace
843 output), then you specify the name of the script to run, then you specify
844 arguments to the script. These arguments to the script are parsed by the bourne
845 shell command line option processor, but are not interpreted as options to the
846 shell itself. Using the CommandLine library, we would specify this as:</p>
849 <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>("-"));
850 <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>"));
851 <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
854 <p>which automatically provides the help output:</p>
857 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
860 -help - display available options (--help-hidden for more)
861 <b>-x - Enable trace output</b>
864 <p>At runtime, if we run our new shell replacement as '<tt>spiffysh -x test.sh
865 -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
866 <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
867 <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
868 were specified after the last positional argument (which is the script
871 <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
872 be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
873 per program, there must be at least one <a href="#positional">positional
874 argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
875 positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
876 href="#cl::list">cl::list</a> option.</p>
880 <!-- ======================================================================= -->
881 <div class="doc_subsection">
882 <a name="storage">Internal vs External Storage</a>
885 <div class="doc_text">
887 <p>By default, all command line options automatically hold the value that they
888 parse from the command line. This is very convenient in the common case,
889 especially when combined with the ability to define command line options in the
890 files that use them. This is called the internal storage model.</p>
892 <p>Sometimes, however, it is nice to separate the command line option processing
893 code from the storage of the value parsed. For example, lets say that we have a
894 '<tt>-debug</tt>' option that we would like to use to enable debug information
895 across the entire body of our program. In this case, the boolean value
896 controlling the debug code should be globally accessable (in a header file, for
897 example) yet the command line option processing code should not be exposed to
898 all of these clients (requiring lots of .cpp files to #include
899 <tt>CommandLine.h</tt>).</p>
901 <p>To do this, set up your .h file with your option, like this for example:</p>
904 <i>// DebugFlag.h - Get access to the '-debug' command line option
907 // DebugFlag - This boolean is set to true if the '-debug' command line option
908 // is specified. This should probably not be referenced directly, instead, use
909 // the DEBUG macro below.
911 extern bool DebugFlag;
913 <i>// DEBUG macro - This macro should be used by code to emit debug information.
914 // In the '-debug' option is specified on the command line, and if this is a
915 // debug build, then the code specified as the option to the macro will be
916 // executed. Otherwise it will not be. Example:
918 // DEBUG(cerr << "Bitset contains: " << Bitset << "\n");
920 <span class="doc_red">#ifdef NDEBUG
923 #define DEBUG(X)</span> \
924 do { if (DebugFlag) { X; } } while (0)
925 <span class="doc_red">#endif</span>
928 <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
929 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
930 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
931 an additial argument to our command line argument processor, and we specify
932 where to fill in with the <a href="#cl::location">cl::location</a>
936 bool DebugFlag; <i>// the actual value</i>
937 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
938 Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>,
939 <a href="#cl::location">cl::location</a>(DebugFlag));
942 <p>In the above example, we specify "<tt>true</tt>" as the second argument to
943 the <a href="#cl::opt">cl::opt</a> template, indicating that the template should
944 not maintain a copy of the value itself. In addition to this, we specify the <a
945 href="#cl::location">cl::location</a> attribute, so that <tt>DebugFlag</tt> is
946 automatically set.</p>
950 <!-- ======================================================================= -->
951 <div class="doc_subsection">
952 <a name="attributes">Option Attributes</a>
955 <div class="doc_text">
957 <p>This section describes the basic attributes that you can specify on
962 <li>The option name attribute (which is required for all options, except <a
963 href="#positional">positional options</a>) specifies what the option name is.
964 This option is specified in simple double quotes:
967 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
972 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
973 description for the option to be shown in the <tt>--help</tt> output for the
976 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
977 specifies a string that can be used to fine tune the <tt>--help</tt> output for
978 a command line option. Look <a href="#value_desc_example">here</a> for an
981 <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
982 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
983 not specified then the command line option value defaults to the value created
984 by the default constructor for the type. <b>Warning</b>: If you specify both
985 <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
986 you must specify <b><tt>cl::location</tt></b> first, so that when the
987 command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
988 initial value. (You will get an error at runtime if you don't put them in
989 the right order.)</li>
991 <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
992 store the value for a parsed command line option if using external storage. See
993 the section on <a href="#storage">Internal vs External Storage</a> for more
996 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
997 specifies which option a <a href="#cl::alias">cl::alias</a> option is an alias
1000 <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
1001 the string-to-value mapping to be used by the generic parser. It takes a
1002 <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
1004 specify the option name, the value mapped to, and the description shown in the
1005 <tt>--help</tt> for the tool. Because the generic parser is used most
1006 frequently with enum values, two macros are often useful:
1010 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
1011 nice simple way to specify a triplet for an enum. This macro automatically
1012 makes the option name be the same as the enum name. The first option to the
1013 macro is the enum, the second is the description for the command line
1016 <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
1017 specify macro options where the option name doesn't equal the enum name. For
1018 this macro, the first argument is the enum value, the second is the flag name,
1019 and the second is the description.</li>
1023 You will get a compile time error if you try to use cl::values with a parser
1024 that does not support it.</li>
1030 <!-- ======================================================================= -->
1031 <div class="doc_subsection">
1032 <a name="modifiers">Option Modifiers</a>
1035 <div class="doc_text">
1037 <p>Option modifiers are the flags and expressions that you pass into the
1038 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1039 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
1040 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
1041 your application well.</p>
1043 <p>These options fall into five main catagories:</p>
1046 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
1047 <li><a href="#numoccurrences">Controlling the number of occurrences
1048 required and allowed</a></li>
1049 <li><a href="#valrequired">Controlling whether or not a value must be
1051 <li><a href="#formatting">Controlling other formatting options</a></li>
1052 <li><a href="#misc">Miscellaneous option modifiers</a></li>
1055 <p>It is not possible to specify two options from the same catagory (you'll get
1056 a runtime error) to a single option, except for options in the miscellaneous
1057 catagory. The CommandLine library specifies defaults for all of these settings
1058 that are the most useful in practice and the most common, which mean that you
1059 usually shouldn't have to worry about these.</p>
1063 <!-- _______________________________________________________________________ -->
1064 <div class="doc_subsubsection">
1065 <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
1068 <div class="doc_text">
1070 <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
1071 <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
1072 appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
1073 compiled program:</p>
1077 <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
1078 (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1079 href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
1080 in both help listings.</li>
1082 <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
1083 default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
1084 the option should not appear in the <tt>--help</tt> output, but should appear in
1085 the <tt>--help-hidden</tt> output.</li>
1087 <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
1088 indicates that the option should not appear in any help output.</li>
1094 <!-- _______________________________________________________________________ -->
1095 <div class="doc_subsubsection">
1096 <a name="numoccurrences">Controlling the number of occurrences required and
1100 <div class="doc_text">
1102 <p>This group of options is used to control how many time an option is allowed
1103 (or required) to be specified on the command line of your program. Specifying a
1104 value for this setting allows the CommandLine library to do error checking for
1107 <p>The allowed values for this option group are:</p>
1111 <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
1112 is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1113 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1114 allow either zero or one occurrence of the option to be specified.</li>
1116 <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
1117 (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
1118 indicates that your program will allow the option to be specified zero or more
1121 <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
1122 indicates that the specified option must be specified exactly one time.</li>
1124 <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
1125 indicates that the option must be specified at least one time.</li>
1127 <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1128 href="#positional">Positional arguments section</a></li>
1132 <p>If an option is not specified, then the value of the option is equal to the
1133 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1134 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1135 option value is initialized with the default constructor for the data type.</p>
1137 <p>If an option is specified multiple times for an option of the <tt><a
1138 href="#cl::opt">cl::opt</a></tt> class, only the last value will be
1143 <!-- _______________________________________________________________________ -->
1144 <div class="doc_subsubsection">
1145 <a name="valrequired">Controlling whether or not a value must be specified</a>
1148 <div class="doc_text">
1150 <p>This group of options is used to control whether or not the option allows a
1151 value to be present. In the case of the CommandLine library, a value is either
1152 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1153 string (e.g. '<tt>-o a.out</tt>').</p>
1155 <p>The allowed values for this option group are:</p>
1159 <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
1160 (which is the default for <tt>bool</tt> typed options) specifies that it is
1161 acceptable to have a value, or not. A boolean argument can be enabled just by
1162 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1163 If an option is specified with this mode, it is illegal for the value to be
1164 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1165 get this behavior, you must use the <a
1166 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
1168 <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
1169 (which is the default for all other types except for <a
1170 href="#onealternative">unnamed alternatives using the generic parser</a>)
1171 specifies that a value must be provided. This mode informs the command line
1172 library that if an option is not provides with an equal sign, that the next
1173 argument provided must be the value. This allows things like '<tt>-o
1174 a.out</tt>' to work.</li>
1176 <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
1177 modifier (which is the default for <a href="#onealternative">unnamed
1178 alternatives using the generic parser</a>) indicates that it is a runtime error
1179 for the user to specify a value. This can be provided to disallow users from
1180 providing options to boolean options (like '<tt>-foo=true</tt>').</li>
1184 <p>In general, the default values for this option group work just like you would
1185 want them to. As mentioned above, you can specify the <a
1186 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1187 argument to restrict your command line parser. These options are mostly useful
1188 when <a href="#extensionguide">extending the library</a>.</p>
1192 <!-- _______________________________________________________________________ -->
1193 <div class="doc_subsubsection">
1194 <a name="formatting">Controlling other formatting options</a>
1197 <div class="doc_text">
1199 <p>The formatting option group is used to specify that the command line option
1200 has special abilities and is otherwise different from other command line
1201 arguments. As usual, you can only specify at most one of these arguments.</p>
1205 <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
1206 modifier (which is the default all options) specifies that this option is
1209 <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
1210 specifies that this is a positional argument, that does not have a command line
1211 option associated with it. See the <a href="#positional">Positional
1212 Arguments</a> section for more information.</li>
1214 <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1215 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
1217 <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
1218 that this option prefixes its value. With 'Prefix' options, there is no equal
1219 sign that separates the value from the option name specified. This is useful
1220 for processing odd arguments like '<tt>-lmalloc -L/usr/lib'</tt> in a linker
1221 tool. Here, the '<tt>l</tt>' and '<tt>L</tt>' options are normal string (list)
1222 options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
1223 allow the CommandLine library to recognize them. Note that <a
1224 href="#cl::Prefix">cl::Prefix</a> options must not have the <a
1225 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li>
1227 <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
1228 to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
1229 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1230 command actually enables four different options, all of which are single
1231 letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
1236 <p>The CommandLine library does not restrict how you use the <a
1237 href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
1238 modifiers, but it is possible to specify ambiguous argument settings. Thus, it
1239 is possible to have multiple letter options that are prefix or grouping options,
1240 and they will still work as designed.</p>
1242 <p>To do this, the CommandLine library uses a greedy algorithm to parse the
1243 input option into (potentially multiple) prefix and grouping options. The
1244 strategy basically looks like this:</p>
1246 <p><tt>parse(string OrigInput) {</tt>
1249 <li><tt>string input = OrigInput;</tt>
1250 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1251 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1252 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1253 <li><tt>if (getOption(input).isPrefix())<br>
1254 return getOption(input).parse(input);</tt>
1255 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1256 getOption(input).parse();<br>
1257 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1258 input = OrigInput;<br>
1259 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1261 <li><tt>if (!OrigInput.empty()) error();</tt></li>
1269 <!-- _______________________________________________________________________ -->
1270 <div class="doc_subsubsection">
1271 <a name="misc">Miscellaneous option modifiers</a>
1274 <div class="doc_text">
1276 <p>The miscellaneous option modifiers are the only flags where you can specify
1277 more than one flag from the set: they are not mutually exclusive. These flags
1278 specify boolean properties that modify the option.</p>
1282 <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
1283 indicates that any commas specified for an option's value should be used to
1284 split the value up into multiple values for the option. For example, these two
1285 options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
1286 "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
1287 makes sense to be used in a case where the option is allowed to accept one or
1288 more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
1290 <li><a name="cl::PositionalEatsArgs">The
1291 <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
1292 positional arguments, and only makes sense for lists) indicates that positional
1293 argument should consume any strings after it (including strings that start with
1294 a "-") up until another recognized positional argument. For example, if you
1295 have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the
1296 string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
1297 -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
1298 "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
1302 <p>So far, these are the only two miscellaneous option modifiers.</p>
1306 <!-- ======================================================================= -->
1307 <div class="doc_subsection">
1308 <a name="toplevel">Top-Level Classes and Functions</a>
1311 <div class="doc_text">
1313 <p>Despite all of the built-in flexibility, the CommandLine option library
1314 really only consists of one function (<a
1315 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1316 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1317 href="#cl::list"><tt>cl::list</tt></a>, and <a
1318 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1319 classes in detail.</p>
1323 <!-- _______________________________________________________________________ -->
1324 <div class="doc_subsubsection">
1325 <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
1329 <div class="doc_text">
1331 <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1332 directly from <tt>main</tt>, and is used to fill in the values of all of the
1333 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1336 <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1337 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1338 which holds <a href="#description">additional extra text</a> to emit when the
1339 <tt>--help</tt> option is invoked.</p>
1343 <!-- _______________________________________________________________________ -->
1344 <div class="doc_subsubsection">
1345 <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
1349 <div class="doc_text">
1351 <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
1353 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
1354 except that it is designed to take values for options from an environment
1355 variable, for those cases in which reading the command line is not convenient or
1356 not desired. It fills in the values of all the command line option variables
1358 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
1361 <p>It takes three parameters: first, the name of the program (since
1362 <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
1363 second, the name of the environment variable to examine, and third, the optional
1364 <a href="#description">additional extra text</a> to emit when the
1365 <tt>--help</tt> option is invoked.</p>
1367 <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
1368 variable's value up into words and then process them using
1369 <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
1370 <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
1371 quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
1372 be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
1373 which is different from what you would get from the shell with the same
1378 <!-- _______________________________________________________________________ -->
1379 <div class="doc_subsubsection">
1380 <a name="cl::opt">The <tt>cl::opt</tt> class</a>
1383 <div class="doc_text">
1385 <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
1386 options, and is the one used most of the time. It is a templated class which
1387 can take up to three arguments (all except for the first have default values
1391 <b>namespace</b> cl {
1392 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1393 <b>class</b> ParserClass = parser<DataType> >
1398 <p>The first template argument specifies what underlying data type the command
1399 line argument is, and is used to select a default parser implementation. The
1400 second template argument is used to specify whether the option should contain
1401 the storage for the option (the default) or whether external storage should be
1402 used to contain the value parsed for the option (see <a href="#storage">Internal
1403 vs External Storage</a> for more information).</p>
1405 <p>The third template argument specifies which parser to use. The default value
1406 selects an instantiation of the <tt>parser</tt> class based on the underlying
1407 data type of the option. In general, this default works well for most
1408 applications, so this option is only used when using a <a
1409 href="#customparser">custom parser</a>.</p>
1413 <!-- _______________________________________________________________________ -->
1414 <div class="doc_subsubsection">
1415 <a name="cl::list">The <tt>cl::list</tt> class</a>
1418 <div class="doc_text">
1420 <p>The <tt>cl::list</tt> class is the class used to represent a list of command
1421 line options. It too is a templated class which can take up to three
1425 <b>namespace</b> cl {
1426 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1427 <b>class</b> ParserClass = parser<DataType> >
1432 <p>This class works the exact same as the <a
1433 href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
1434 the <b>type</b> of the external storage, not a boolean value. For this class,
1435 the marker type '<tt>bool</tt>' is used to indicate that internal storage should
1440 <!-- _______________________________________________________________________ -->
1441 <div class="doc_subsubsection">
1442 <a name="cl::alias">The <tt>cl::alias</tt> class</a>
1445 <div class="doc_text">
1447 <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1448 aliases for other arguments.</p>
1451 <b>namespace</b> cl {
1456 <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
1457 used to specify which option this is an alias for. Alias arguments default to
1458 being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
1459 the conversion from string to data.</p>
1463 <!-- ======================================================================= -->
1464 <div class="doc_subsection">
1465 <a name="builtinparsers">Builtin parsers</a>
1468 <div class="doc_text">
1470 <p>Parsers control how the string value taken from the command line is
1471 translated into a typed value, suitable for use in a C++ program. By default,
1472 the CommandLine library uses an instance of <tt>parser<type></tt> if the
1473 command line option specifies that it uses values of type '<tt>type</tt>'.
1474 Because of this, custom option processing is specified with specializations of
1475 the '<tt>parser</tt>' class.</p>
1477 <p>The CommandLine library provides the following builtin parser
1478 specializations, which are sufficient for most applications. It can, however,
1479 also be extended to work with new data types and new ways of interpreting the
1480 same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
1481 details on this type of library extension.</p>
1485 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
1486 can be used to map strings values to any data type, through the use of the <a
1487 href="#cl::values">cl::values</a> property, which specifies the mapping
1488 information. The most common use of this parser is for parsing enum values,
1489 which allows you to use the CommandLine library for all of the error checking to
1490 make sure that only valid enum values are specified (as opposed to accepting
1491 arbitrary strings). Despite this, however, the generic parser class can be used
1492 for any data type.</li>
1494 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
1495 is used to convert boolean strings to a boolean value. Currently accepted
1496 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1497 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
1499 <li><a name="stringparser">The <b><tt>parser<string></tt>
1500 specialization</b></a> simply stores the parsed string into the string value
1501 specified. No conversion or modification of the data is performed.</li>
1503 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
1504 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1505 accept a decimal number (with an optional '+' or '-' prefix) which must start
1506 with a non-zero digit. It accepts octal numbers, which are identified with a
1507 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1508 '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
1510 <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
1511 <b><tt>parser<float></tt> specializations</b> use the standard C
1512 <tt>strtod</tt> function to convert floating point strings into floating point
1513 values. As such, a broad range of string formats is supported, including
1514 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1521 <!-- *********************************************************************** -->
1522 <div class="doc_section">
1523 <a name="extensionguide">Extension Guide</a>
1525 <!-- *********************************************************************** -->
1527 <div class="doc_text">
1529 <p>Although the CommandLine library has a lot of functionality built into it
1530 already (as discussed previously), one of its true strengths lie in its
1531 extensibility. This section discusses how the CommandLine library works under
1532 the covers and illustrates how to do some simple, common, extensions.</p>
1536 <!-- ======================================================================= -->
1537 <div class="doc_subsection">
1538 <a name="customparser">Writing a custom parser</a>
1541 <div class="doc_text">
1543 <p>One of the simplest and most common extensions is the use of a custom parser.
1544 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1545 of the CommandLine library that turns string input from the user into a
1546 particular parsed data type, validating the input in the process.</p>
1548 <p>There are two ways to use a new parser:</p>
1554 <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1555 your custom data type.<p>
1557 <p>This approach has the advantage that users of your custom data type will
1558 automatically use your custom parser whenever they define an option with a value
1559 type of your data type. The disadvantage of this approach is that it doesn't
1560 work if your fundemental data type is something that is already supported.</p>
1566 <p>Write an independent class, using it explicitly from options that need
1569 <p>This approach works well in situations where you would line to parse an
1570 option using special syntax for a not-very-special data-type. The drawback of
1571 this approach is that users of your parser have to be aware that they are using
1572 your parser, instead of the builtin ones.</p>
1578 <p>To guide the discussion, we will discuss a custom parser that accepts file
1579 sizes, specified with an optional unit after the numeric size. For example, we
1580 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1581 this case, the underlying data type we want to parse into is
1582 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1583 this the default for all <tt>unsigned</tt> options.</p>
1585 <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
1588 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1589 <i>// parse - Return true on error.</i>
1590 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1591 <b>unsigned</b> &Val);
1595 <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
1596 fill in the default, boiler plate, code for us. We give it the data type that
1597 we parse into (the last argument to the <tt>parse</tt> method so that clients of
1598 our custom parser know what object type to pass in to the parse method (here we
1599 declare that we parse into '<tt>unsigned</tt>' variables.</p>
1601 <p>For most purposes, the only method that must be implemented in a custom
1602 parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
1603 whenever the option is invoked, passing in the option itself, the option name,
1604 the string to parse, and a reference to a return value. If the string to parse
1605 is not well formed, the parser should output an error message and return true.
1606 Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
1607 our example, we implement <tt>parse</tt> as:</p>
1610 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1611 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1612 <b>const char</b> *ArgStart = Arg.c_str();
1615 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1616 Val = (unsigned)strtol(ArgStart, &End, 0);
1619 <b>switch</b> (*End++) {
1620 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1621 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1622 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1625 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1626 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1627 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1630 <i>// Print an error message if unrecognized character!</i>
1631 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1637 <p>This function implements a very simple parser for the kinds of strings we are
1638 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1639 example), it is good enough for this example. Note that we use the option
1640 itself to print out the error message (the <tt>error</tt> method always returns
1641 true) in order to get a nice error message (shown below). Now that we have our
1642 parser class, we can use it like this:</p>
1645 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1646 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1647 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1650 <p>Which adds this to the output of our program:</p>
1654 -help - display available options (--help-hidden for more)
1656 <b>-max-file-size=<size> - Maximum file size to accept</b>
1659 <p>And we can test that our parse works correctly now (the test program just
1660 prints out the max-file-size argument value):</p>
1665 $ ./test -max-file-size=123MB
1667 $ ./test -max-file-size=3G
1669 $ ./test -max-file-size=dog
1670 -max-file-size option: 'dog' value invalid for file size argument!
1673 <p>It looks like it works. The error message that we get is nice and helpful,
1674 and we seem to accept reasonable file sizes. This wraps up the "custom parser"
1679 <!-- ======================================================================= -->
1680 <div class="doc_subsection">
1681 <a name="explotingexternal">Exploiting external storage</a>
1684 <div class="doc_text">
1686 <p>TODO: fill in this section</p>
1690 <!-- ======================================================================= -->
1691 <div class="doc_subsection">
1692 <a name="dynamicopts">Dynamically adding command line options</a>
1695 <div class="doc_text">
1697 <p>TODO: fill in this section</p>
1701 <!-- *********************************************************************** -->
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