1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2 <html><head><title>CommandLine 2.0 Library Manual</title></head>
5 <table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
6 <tr><td> <font size=+3 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>CommandLine 2.0 Library Manual</b></font></td>
10 <li><a href="#introduction">Introduction</a>
11 <li><a href="#quickstart">Quick Start Guide</a>
13 <li><a href="#bool">Boolean Arguments</a>
14 <li><a href="#alias">Argument Aliases</a>
15 <li><a href="#onealternative">Selecting an alternative from a
16 set of possibilities</a>
17 <li><a href="#namedalternatives">Named alternatives</a>
18 <li><a href="#list">Parsing a list of options</a>
19 <li><a href="#description">Adding freeform text to help output</a>
21 <li><a href="#referenceguide">Reference Guide</a>
23 <li><a href="#positional">Positional Arguments</a>
25 <li><a href="#--">Specifying positional options with hyphens</a>
26 <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
29 <li><a href="#storage">Internal vs External Storage</a>
30 <li><a href="#attributes">Option Attributes</a>
31 <li><a href="#modifiers">Option Modifiers</a>
33 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a>
34 <li><a href="#numoccurances">Controlling the number of occurances
35 required and allowed</a>
36 <li><a href="#valrequired">Controlling whether or not a value must be
38 <li><a href="#formatting">Controlling other formatting options</a>
40 <li><a href="#toplevel">Top-Level Classes and Functions</a>
42 <li><a href="#cl::ParseCommandLineOptions">The
43 <tt>cl::ParseCommandLineOptions</tt> function</a>
44 <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a>
45 <li><a href="#cl::list">The <tt>cl::list</tt> class</a>
46 <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a>
48 <li><a href="#builtinparsers">Builtin parsers</a>
50 <li><a href="#genericparser">The Generic <tt>parser<t></tt>
52 <li><a href="#boolparser">The <tt>parser<bool></tt>
54 <li><a href="#stringparser">The <tt>parser<string></tt>
56 <li><a href="#intparser">The <tt>parser<int></tt>
58 <li><a href="#doubleparser">The <tt>parser<double></tt> and
59 <tt>parser<float></tt> specializations</a>
62 <li><a href="#extensionguide">Extension Guide</a>
64 <li><a href="#customparser">Writing a custom parser</a>
65 <li><a href="#explotingexternal">Exploiting external storage</a>
66 <li><a href="#dynamicopts">Dynamically adding command line options</a>
69 <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p>
73 <!-- *********************************************************************** -->
74 <table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
75 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
76 <a name="introduction">Introduction
77 </b></font></td></tr></table><ul>
78 <!-- *********************************************************************** -->
80 This document describes the CommandLine argument processing library. It will
81 show you how to use it, and what it can do. The CommandLine library uses a
82 declarative approach to specifying the command line options that your program
83 takes. By default, these options declarations implicitly hold the value parsed
84 for the option declared (of course this <a href="#storage">can be
87 Although there are a <b>lot</b> of command line argument parsing libraries out
88 there in many different languages, none of them fit well with what I needed. By
89 looking at the features and problems of other libraries, I designed the
90 CommandLine library to have the following features:<p>
93 <li>Speed: The CommandLine library is very quick and uses little resources. The
94 parsing time of the library is directly proportional to the number of arguments
95 parsed, not the the number of options recognized. Additionally, command line
96 argument values are captured transparently into user defined variables, which
97 can be accessed like any other variable (and with the same performance).<p>
99 <li>Type Safe: As a user of CommandLine, you don't have to worry about
100 remembering the type of arguments that you want (is it an int? a string? a
101 bool? an enum?) and keep casting it around. Not only does this help prevent
102 error prone constructs, it also leads to dramatically cleaner source code.<p>
104 <li>No subclasses required: To use CommandLine, you instantiate variables that
105 correspond to the arguments that you would like to capture, you don't subclass a
106 parser. This means that you don't have to write <b>any</b> boilerplate code.<p>
108 <li>Globally accessible: Libraries can specify command line arguments that are
109 automatically enabled in any tool that links to the library. This is possible
110 because the application doesn't have to keep a "list" of arguments to pass to
111 the parser. This also makes supporting <a href="#dynamicopts">dynamically
112 loaded options</a> trivial.<p>
114 <li>Cleaner: CommandLine supports enum and other types directly, meaning that
115 there is less error and more security built into the library. You don't have to
116 worry about whether your integral command line argument accidentally got
117 assigned a value that is not valid for your enum type.<p>
119 <li>Powerful: The CommandLine library supports many different types of
120 arguments, from simple <a href="#boolparser">boolean flags</a> to <a
121 href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
122 href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
123 href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
124 arguments</a>. This is possible because CommandLine is...<p>
126 <li>Extensible: It is very simple to add a new argument type to CommandLine.
127 Simply specify the parser that you want to use with the command line option when
128 you declare it. <a href="#customparser">Custom parsers</a> are no problem.<p>
130 <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
131 that you, the user, have to do. For example, it automatically provides a
132 <tt>--help</tt> option that shows the available command line options for your
133 tool. Additionally, it does most of the basic correctness checking for you.<p>
135 <li>Capable: The CommandLine library can handle lots of different forms of
136 options often found in real programs. For example, <a
137 href="#positional">positional</a> arguments, <tt>ls</tt> style <a
138 href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
139 -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
140 options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
141 href="#cl::ConsumeAfter">interpreter style options</a>.<p>
145 This document will hopefully let you jump in and start using CommandLine in your
146 utility quickly and painlessly. Additionally it should be a simple reference
147 manual to figure out how stuff works. If it is failing in some area (or you
148 want an extension to the library), nag the author, <a
149 href="mailto:sabre@nondot.org">Chris Lattner</a>.<p>
153 <!-- *********************************************************************** -->
154 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
155 <a name="quickstart">Quick Start Guide
156 </b></font></td></tr></table><ul>
157 <!-- *********************************************************************** -->
159 This section of the manual runs through a simple CommandLine'ification of a
160 basic compiler tool. This is intended to show you how to jump into using the
161 CommandLine library in your own program, and show you some of the cool things it
164 To start out, you need to include the CommandLine header file into your
168 #include "Support/CommandLine.h"
171 Additionally, you need to add this as the first line of your main program:<p>
174 int main(int argc, char **argv) {
175 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
180 ... which actually parses the arguments and fills in the variable
183 Now that you are ready to support command line arguments, we need to tell the
184 system which ones we want, and what type of argument they are. The CommandLine
185 library uses a declarative syntax to model cammand line arguments with the
186 variable declarations that capture the parsed values. This means that for every
187 command line option that you would like to support, there should be a variable
188 declaration to capture the result. For example, in a compiler, we would like to
189 support the unix standard '<tt>-o <filename></tt>' option to specify where
190 to put the output. With the CommandLine library, this is represented like
193 <pre><a name="value_desc_example">
194 <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>"));
197 This declares a variable "<tt>OutputFilename</tt>" that is used to capture the
198 result of the "<tt>o</tt>" argument (first parameter). We specify that this is
199 a simple scalar option by using the "<tt><a href="#cl::opt">cl::opt</a></tt>"
200 template (as opposed to the <a href="#list">"<tt>cl::list</tt>
201 template</a>), and tell the CommandLine library that the data type that we are
202 parsing is a string.<p>
204 The second and third parameters (which are optional) are used to specify what to
205 output for the "<tt>--help</tt>" option. In this case, we get a line that looks
209 USAGE: compiler [options]
212 -help - display available options (--help-hidden for more)
213 <b>-o <filename> - Specify output filename</b>
216 Because we specified that the command line option should parse using the
217 <tt>string</tt> data type, the variable declared is automatically usable as a
218 real string in all contexts that a normal C++ string object may be used. For
223 ofstream Output(OutputFilename.c_str());
228 There are many different options that you can use to customize the command line
229 option handling library, but the above example shows the general interface to
230 these options. The options can be specified in any order, and are specified
231 with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
232 there are no positional dependencies to remember. The available options are
233 discussed in detail in the <a href="#referenceguide">Reference Guide</a>.<p>
236 Continuing the example, we would like to have our compiler take an input
237 filename as well as an output filename, but we do not want the input filename to
238 be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
239 style of argument, the CommandLine library allows for <a
240 href="#positional">positional</a> arguments to be specified for the program.
241 These positional arguments are filled with command line parameters that are not
242 in option form. We use this feature like this:<p>
245 <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>"));
248 This declaration indicates that the first positional argument should be treated
249 as the input filename. Here we use the <tt><a
250 href="#cl::init">cl::init</a></tt> option to specify an initial value for the
251 command line option, which is used if the option is not specified (if you do not
252 specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
253 the default constructor for the data type is used to initialize the value).
254 Command line options default to being optional, so if we would like to require
255 that the user always specify an input filename, we would add the <tt><a
256 href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
257 <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:<p>
260 <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>);
263 Again, the CommandLine library does not require the options to be specified in
264 any particular order, so the above declaration is equivalent to:<p>
267 <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>"));
270 By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag, the
271 CommandLine library will automatically issue an error if the argument is not
272 specified, which shifts all of the command line option verification code out of
273 your application into the library. This is just one example of how using flags
274 can alter the default behaviour of the library, on a per-option basis. By
275 adding one of the declarations above, the <tt>--help</tt> option synopsis is now
279 USAGE: compiler [options] <b><input file></b>
282 -help - display available options (--help-hidden for more)
283 -o <filename> - Specify output filename
286 ... indicating that an input filename is expected.<p>
290 <!-- ======================================================================= -->
291 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
292 <a name="bool">Boolean Arguments
293 </b></font></td></tr></table><ul>
295 In addition to input and output filenames, we would like the compiler example to
296 support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
297 file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
298 compatibility with some of our users. We can support these by declaring options
299 of boolean type like this:<p>
302 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
303 <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>"));
304 <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>);
307 This does what you would expect: it declares three boolean variables
308 ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
309 options. Note that the "<tt>-q</tt>" option is specified with the "<a
310 href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
311 from being shown by the standard "<tt>--help</tt>" output (note that it is still
312 shown in the "<tt>--help-hidden</tt>" output).<p>
314 The CommandLine library uses a <a href="#builtinparsers">different parser</a>
315 for different data types. For example, in the string case, the argument passed
316 to the option is copied literally into the content of the string variable... we
317 obviously cannot do that in the boolean case, however, so we must use a smarter
318 parser. In the case of the boolean parser, it allows no options (in which case
319 it assigns the value of true to the variable), or it allows the values
320 "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
324 compiler -f # No value, 'Force' == true
325 compiler -f=true # Value specified, 'Force' == true
326 compiler -f=TRUE # Value specified, 'Force' == true
327 compiler -f=FALSE # Value specified, 'Force' == false
330 ... you get the idea. The <a href="#boolparser">bool parser</a> just turns the
331 string values into boolean values, and rejects things like '<tt>compiler
332 -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
333 href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
334 like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
335 library calls to parse the string value into the specified data type.<p>
337 With the declarations above, "<tt>compiler --help</tt>" emits this:<p>
340 USAGE: compiler [options] <input file>
343 <b>-f - Overwrite output files</b>
344 -o - Override output filename
345 <b>-quiet - Don't print informational messages</b>
346 -help - display available options (--help-hidden for more)
349 and "<tt>opt --help-hidden</tt>" prints this:<p>
352 USAGE: compiler [options] <input file>
355 -f - Overwrite output files
356 -o - Override output filename
357 <b>-q - Don't print informational messages</b>
358 -quiet - Don't print informational messages
359 -help - display available options (--help-hidden for more)
362 This brief example has shown you how to use the '<tt><a
363 href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
364 arguments. In addition to simple scalar arguments, the CommandLine library also
365 provides primitives to support CommandLine option <a href="#alias">aliases</a>,
366 and <a href="#list">lists</a> of options.<p>
369 <!-- ======================================================================= -->
370 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
371 <a name="alias">Argument Aliases
372 </b></font></td></tr></table><ul>
374 So far, the example works well, except for the fact that we need to check the
375 quiet condition like this now:<p>
379 if (!Quiet && !Quiet2) printInformationalMessage(...);
383 ... which is a real pain! Instead of defining two values for the same
384 condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
385 option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
389 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
390 <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>"));
391 <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));
394 The third line (which is the only one we modified from above) defines a
395 "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by
396 the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
397 specified. Because aliases do not hold state, the only thing the program has to
398 query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
399 that they automatically hide themselves from the <tt>-help</tt> output
400 (although, again, they are still visible in the <tt>--help-hidden
403 Now the application code can simply use:<p>
407 if (!Quiet) printInformationalMessage(...);
411 ... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>" can be used to specify an
412 alternative name for any variable type, and has many uses.<p>
416 <!-- ======================================================================= -->
417 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
418 <a name="onealternative">Selecting an alternative from a set of possibilities
419 </b></font></td></tr></table><ul>
421 So far, we have seen how the CommandLine library handles builtin types like
422 <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
423 things it doesn't know about, like enums or '<tt>int*</tt>'s?<p>
425 The answer is that it uses a table driven generic parser (unless you specify
426 your own parser, as described in the <a href="#extensionguide">Extension
427 Guide</a>). This parser maps literal strings to whatever type is required, are
428 requires you to tell it what this mapping should be.<p>
430 Lets say that we would like to add four optimizations levels to our optimizer,
431 using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>", "<tt>-O1</tt>", and
432 "<tt>-O2</tt>". We could easily implement this with boolean options like above,
433 but there are several problems with this strategy:<p>
436 <li>A user could specify more than one of the options at a time, for example,
437 "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this
438 erroneous input for us.
440 <li>We would have to test 4 different variables to see which ones are set.
442 <li>This doesn't map to the numeric levels that we want... so we cannot easily
443 see if some level >= "<tt>-O1</tt>" is enabled.
447 To cope with these problems, we can use an enum value, and have the CommandLine
448 library fill it in with the appropriate level directly, which is used like
456 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
457 <a href="#cl::values">cl::values</a>(
458 clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
459 clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
460 clEnumVal(O2, "<i>Enable default optimizations</i>"),
461 clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
465 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
469 This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
470 "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
471 that are listed in the declaration (Note that the declaration list must be
472 terminated with the "<tt>0</tt>" argument!). The CommandLine library enforces
473 that the user can only specify one of the options, and it ensure that only valid
474 enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
475 command line arguments matched the enum values. With this option added, our
476 help output now is:<p>
479 USAGE: compiler [options] <input file>
482 <b>Choose optimization level:
483 -g - No optimizations, enable debugging
484 -O1 - Enable trivial optimizations
485 -O2 - Enable default optimizations
486 -O3 - Enable expensive optimizations</b>
487 -f - Overwrite output files
488 -help - display available options (--help-hidden for more)
489 -o <filename> - Specify output filename
490 -quiet - Don't print informational messages
493 In this case, it is sort of awkward that flag names correspond directly to enum
494 names, because we probably don't want a enum definition named "<tt>g</tt>" in
495 our program. Because of this, we can alternatively write this example like
503 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
504 <a href="#cl::values">cl::values</a>(
505 clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
506 clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
507 clEnumVal(O2 , "<i>Enable default optimizations</i>"),
508 clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
512 if (OptimizationLevel == Debug) outputDebugInfo(...);
516 By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we can
517 directly specify the name that the flag should get. In general a direct mapping
518 is nice, but sometimes you can't or don't want to preserve the mapping, which is
519 when you would use it.<p>
523 <!-- ======================================================================= -->
524 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
525 <a name="namedalternatives">Named Alternatives
526 </b></font></td></tr></table><ul>
528 Another useful argument form is a named alternative style. We shall use this
529 style in our compiler to specify different debug levels that can be used.
530 Instead of each debug level being its own switch, we want to support the
531 following options, of which only one can be specified at a time:
532 "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
533 "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
534 our optimization level flags, but we also specify an option name. For this
535 case, the code looks like this:<p>
539 nodebuginfo, quick, detailed
542 // Enable Debug Options to be specified on the command line
543 <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>"),
544 <a href="#cl::values">cl::values</a>(
545 clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
546 clEnumVal(quick, "<i>enable quick debug information</i>"),
547 clEnumVal(detailed, "<i>enable detailed debug information</i>"),
551 This definition defines an enumerated command line variable of type "<tt>enum
552 DebugLev</tt>", which works exactly the same way as before. The difference here
553 is just the interface exposed to the user of your program and the help output by
554 the "<tt>--help</tt>" option:<p>
557 USAGE: compiler [options] <input file>
560 Choose optimization level:
561 -g - No optimizations, enable debugging
562 -O1 - Enable trivial optimizations
563 -O2 - Enable default optimizations
564 -O3 - Enable expensive optimizations
565 <b>-debug_level - Set the debugging level:
566 =none - disable debug information
567 =quick - enable quick debug information
568 =detailed - enable detailed debug information</b>
569 -f - Overwrite output files
570 -help - display available options (--help-hidden for more)
571 -o <filename> - Specify output filename
572 -quiet - Don't print informational messages
575 Again, the only structural difference between the debug level declaration and
576 the optimiation level declaration is that the debug level declaration includes
577 an option name (<tt>"debug_level"</tt>), which automatically changes how the
578 library processes the argument. The CommandLine library supports both forms so
579 that you can choose the form most appropriate for your application.<p>
583 <!-- ======================================================================= -->
584 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
585 <a name="list">Parsing a list of options
586 </b></font></td></tr></table><ul>
588 Now that we have the standard run of the mill argument types out of the way,
589 lets get a little wild and crazy. Lets say that we want our optimizer to accept
590 a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
591 might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
592 this case, the order of the arguments and the number of appearances is very
593 important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
594 template is for. First, start by defining an enum of the optimizations that you
595 would like to perform:<p>
599 // 'inline' is a C++ keyword, so name it 'inlining'
600 dce, constprop, inlining, strip
604 Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:<p>
607 <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
608 <a href="#cl::values">cl::values</a>(
609 clEnumVal(dce , "<i>Dead Code Elimination</i>"),
610 clEnumVal(constprop , "<i>Constant Propogation</i>"),
611 clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
612 clEnumVal(strip , "<i>Strip Symbols</i>"),
616 This defines a variable that is conceptually of the type
617 "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
621 for (unsigned i = 0; i != OptimizationList.size(); ++i)
622 switch (OptimizationList[i])
626 ... to iterate through the list of options specified.<p>
628 Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is completely general and may be used
629 with any data types or other arguments that you can use with the
630 "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One especially useful way to use a list is to
631 capture all of the positional arguments together if there may be more than one
632 specified. In the case of a linker, for example, the linker takes several
633 '<tt>.o</tt>' files, and needs to capture them into a list. This is naturally
638 <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>);
642 This variable works just like a "<tt>vector<string></tt>" object. As
643 such, accessing the list is simple, just like above. In this example, we used
644 the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
645 CommandLine library that it is an error if the user does not specify any
646 <tt>.o</tt> files on our command line. Again, this just reduces the amount of
647 checking we have to do.<p>
651 <!-- ======================================================================= -->
652 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
653 <a name="description">Adding freeform text to help output
654 </b></font></td></tr></table><ul>
656 As our program grows and becomes more mature, we may decide to put summary
657 information about what it does into the help output. The help output is styled
658 to look similar to a Unix <tt>man</tt> page, providing concise information about
659 a program. Unix <tt>man</tt> pages, however often have a description about what
660 the program does. To add this to your CommandLine program, simply pass a third
662 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
663 call in main. This additional argument is then printed as the overview
664 information for your program, allowing you to include any additional information
665 that you want. For example:<p>
668 int main(int argc, char **argv) {
669 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
670 " This program blah blah blah...\n");
675 Would yield the help output:
678 <b>OVERVIEW: CommandLine compiler example
680 This program blah blah blah...</b>
682 USAGE: compiler [options] <input file>
686 -help - display available options (--help-hidden for more)
687 -o <filename> - Specify output filename
693 <!-- *********************************************************************** -->
694 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
695 <a name="referenceguide">Reference Guide
696 </b></font></td></tr></table><ul>
697 <!-- *********************************************************************** -->
699 Now that you know the basics of how to use the CommandLine library, this section
700 will give you the detailed information you need to tune how command line options
701 work, as well as information on more "advanced" command line option processing
705 <!-- ======================================================================= -->
706 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
707 <a name="positional">Positional Arguments
708 </b></font></td></tr></table><ul>
710 Positional arguments are those arguments that are not named, and are not
711 specified with a hyphen. Positional arguments should be used when an option is
712 specified by its position alone. For example, the standard Unix <tt>grep</tt>
713 tool takes a regular expression argument, and an optional filename to search
714 through (which defaults to standard input if a filename is not specified).
715 Using the CommandLine library, this would be specified as:<p>
718 <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>);
719 <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>"));
722 Given these two option declarations, the <tt>--help</tt> output for our grep
723 replacement would look like this:<p>
726 USAGE: spiffygrep [options] <b><regular expression> <input file></b>
729 -help - display available options (--help-hidden for more)
732 ... and the resultant program could be used just like the standard <tt>grep</tt>
735 Positional arguments are sorted by their order of construction. This means that
736 command line options will be ordered according to how they are listed in a .cpp
737 file, but will not have an ordering defined if they positional arguments are
738 defined in multiple .cpp files. The fix for this problem is simply to define
739 all of your positional arguments in one .cpp file.<p>
743 <!-- _______________________________________________________________________ -->
744 </ul><a name="--"><h4><hr size=0>Specifying positional options with hyphens</h4><ul>
746 Sometimes you may want to specify a value to your positional argument that
747 starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
748 first, you will have trouble doing this, because it will try to find an argument
749 named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
750 Note that the system <tt>grep</tt> has the same problem:<p>
753 $ spiffygrep '-foo' test.txt
754 Unknown command line argument '-foo'. Try: spiffygrep --help'
756 $ grep '-foo' test.txt
757 grep: illegal option -- f
758 grep: illegal option -- o
759 grep: illegal option -- o
760 Usage: grep -hblcnsviw pattern file . . .
763 The solution for this problem is the same for both your tool and the system
764 version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
765 the command line, it is telling the program that all options after the
766 '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
767 can use it like this:<p>
770 $ spiffygrep -- -foo test.txt
776 <!-- _______________________________________________________________________ -->
777 </ul><a name="cl::ConsumeAfter"><h4><hr size=0>The <tt>cl::ConsumeAfter</tt> modifier</h4><ul>
779 The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
780 used to construct programs that use "interpreter style" option processing. With
781 this style of option processing, all arguments specified after the last
782 positional argument are treated as special interpreter arguments that are not
783 interpreted by the command line argument.<p>
785 As a concrete example, lets say we are developing a replacement for the standard
786 Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first you
787 specify options to the shell itself (like <tt>-x</tt> which turns on trace
788 output), then you specify the name of the script to run, then you specify
789 arguments to the script. These arguments to the script are parsed by the bourne
790 shell command line option processor, but are not interpreted as options to the
791 shell itself. Using the CommandLine library, we would specify this as:<p>
794 <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>("-"));
795 <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>"));
796 <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
799 which automatically provides the help output:<p>
802 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
805 -help - display available options (--help-hidden for more)
806 <b>-x - Enable trace output</b>
809 At runtime, if we run our new shell replacement as '<tt>spiffysh -x test.sh -a
810 -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
811 <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
812 <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because
813 they were specified after the last positional argument (which is the script
816 There are several limitations to when <tt>cl::ConsumeAfter</tt> options can be
817 specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified per
818 program, there must be at least one <a href="#positional">positional
819 argument</a> specified, and the <tt>cl::ConsumeAfter</tt> option should be a <a
820 href="#cl::list">cl::list</a> option.<p>
824 <!-- ======================================================================= -->
825 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
826 <a name="storage">Internal vs External Storage
827 </b></font></td></tr></table><ul>
829 By default, all command line options automatically hold the value that they
830 parse from the command line. This is very convenient in the common case,
831 especially when combined with the ability to define command line options in the
832 files that use them. This is called the internal storage model.<p>
834 Sometimes, however, it is nice to separate the command line option processing
835 code from the storage of the value parsed. For example, lets say that we have a
836 '<tt>-debug</tt>' option that we would like to use to enable debug information
837 across the entire body of our program. In this case, the boolean value
838 controlling the debug code should be globally accessable (in a header file, for
839 example) yet the command line option processing code should not be exposed to
840 all of these clients (requiring lots of .cpp files to #include
841 <tt>CommandLine.h</tt>).<p>
843 To do this, set up your .h file with your option, like this for example:<p>
846 <i>// DebugFlag.h - Get access to the '-debug' command line option
849 // DebugFlag - This boolean is set to true if the '-debug' command line option
850 // is specified. This should probably not be referenced directly, instead, use
851 // the DEBUG macro below.
853 extern bool DebugFlag;
855 <i>// DEBUG macro - This macro should be used by code to emit debug information.
856 // In the '-debug' option is specified on the command line, and if this is a
857 // debug build, then the code specified as the option to the macro will be
858 // executed. Otherwise it will not be. Example:
860 // DEBUG(cerr << "Bitset contains: " << Bitset << "\n");
862 <font color=red>#ifdef NDEBUG
865 #define DEBUG(X)</font> \
866 do { if (DebugFlag) { X; } } while (0)
867 <font color=red>#endif</font>
870 This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
871 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
872 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
873 an additial argument to our command line argument processor, and we specify
874 where to fill in with the <a href="#cl::location">cl::location</a> attribute:<p>
877 bool DebugFlag; <i>// the actual value</i>
878 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
879 Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>")</a>, <a href="#cl::Hidden">cl::Hidden</a>,
880 <a href="#cl::location">cl::location</a>(DebugFlag));
883 In the above example, we specify "<tt>true</tt>" as the second argument to the
884 <a href="#cl::opt">cl::opt</a> template, indicating that the template should not
885 maintain a copy of the value itself. In addition to this, we specify the <a
886 href="#cl::location">cl::location</a> attribute, so that <tt>DebugFlag</tt> is
887 automatically set.<p>
891 <!-- ======================================================================= -->
892 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
893 <a name="attributes">Option Attributes
894 </b></font></td></tr></table><ul>
896 This section describes the basic attributes that you can specify on options.<p>
900 <li>The option name attribute (which is required for all options, except <a
901 href="#positional">positional options</a>) specifies what the option name is.
902 This option is specified in simple double quotes:<p>
905 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
908 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b> attribute specifies a
909 description for the option to be shown in the <tt>--help</tt> output for the
912 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b> attribute
913 specifies a string that can be used to fine tune the <tt>--help</tt> output for
914 a command line option. Look <a href="#value_desc_example">here</a> for an
917 <li><a name="cl::init">The <b><tt>cl::init</tt></b> attribute specifies an
918 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
919 not specified then the command line option value defaults to the value created
920 by the default constructor for the type.<p>
922 <li><a name="cl::location">The <b><tt>cl::location</tt></b> attribute where to
923 store the value for a parsed command line option if using external storage. See
924 the section on <a href="#storage">Internal vs External Storage</a> for more
927 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b> attribute specifies
928 which option a <a href="#cl::alias">cl::alias</a> option is an alias for.<p>
930 <li><a name="cl::values">The <b><tt>cl::values</tt></b> attribute specifies the
931 string-to-value mapping to be used by the generic parser. It takes a <b>null
932 terminated</b> list of (option, value, description) triplets that specify the
933 option name, the value mapped to, and the description shown in the
934 <tt>--help</tt> for the tool. Because the generic parser is used most frequently with enum values, two macros are often useful:<p>
936 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b> macro is used as a nice
937 simple way to specify a triplet for an enum. This macro automatically makes the
938 option name be the same as the enum name. The first option to the macro is the
939 enum, the second is the description for the command line option.<p> <li><a
940 name="clEnumValN">The <b><tt>clEnumValN</tt></b> macro is used to specify macro
941 options where the option name doesn't equal the enum name. For this macro, the
942 first argument is the enum value, the second is the flag name, and the second is
946 You will get a compile time error if you try to use cl::values with a parser
947 that does not support it.<p>
953 <!-- ======================================================================= -->
954 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
955 <a name="modifiers">Option Modifiers
956 </b></font></td></tr></table><ul>
958 Option modifiers are the flags and expressions that you pass into the
959 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
960 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
961 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
962 your application well.<p>
964 These options naturally fall into four main catagories:<p>
967 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a>
968 <li><a href="#numoccurances">Controlling the number of occurances
969 required and allowed</a>
970 <li><a href="#valrequired">Controlling whether or not a value must be
972 <li><a href="#formatting">Controlling other formatting options</a>
975 It is not possible to specify two options from the same catagory (you'll get a
976 runtime error) to a single option. The CommandLine library specifies defaults
977 for all of these settings that are the most useful in practice and the most
978 common, which mean that you usually shouldn't have to worry about these.<p>
981 <!-- _______________________________________________________________________ -->
982 </ul><a name="hiding"><h4><hr size=0>Hiding an option from <tt>--help</tt> output</h4><ul>
984 The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and <tt>cl::ReallyHidden</tt>
985 modifiers are used to control whether or not an option appears in the
986 <tt>--help</tt> and <tt>--help-hidden</tt> output for the compiled program:<p>
990 <a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b> modifier (which is the
991 default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
992 href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
993 in both help listings.<p>
995 <a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b> modifier (which is the
996 default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
997 the option should not appear in the <tt>--help</tt> output, but should appear in
998 the <tt>--help-hidden</tt> output.<p>
1000 <a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b> modifier,
1001 indicates that the option should not appear in any help output.<p>
1004 <!-- _______________________________________________________________________ -->
1005 </ul><a name="numoccurances"><h4><hr size=0>Controlling the number of occurances required and allowed</h4><ul>
1007 This group of options is used to control how many time an option is allowed (or
1008 required) to be specified on the command line of your program. Specifying a
1009 value for this setting allows the CommandLine library to do error checking for
1012 The allowed values for this option group are:<p>
1015 <a name="cl::Optional">The <b><tt>cl::Optional</tt></b> modifier (which is the
1016 default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1017 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1018 allow either zero or one occurance of the option to be specified.<p>
1020 <a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b> modifier (which is
1021 the default for the <tt><a href="#cl::list">cl::list</a></tt> class) indicates
1022 that your program will allow the option to be specified zero or more times.<p>
1024 <a name="cl::Required">The <b><tt>cl::Required</tt></b> modifier indicates that
1025 the specified option must be specified exactly one time.<p>
1027 <a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b> modifier indicates
1028 that the option must be specified at least one time.<p>
1030 The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1031 href="#positional">Positional arguments section</a><p>
1035 If an option is not specified, then the value of the option is equal to the
1036 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1037 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1038 option value is initialized with the default constructor for the data type.<p>
1040 If an option is specified multiple times for an option of the <tt><a
1041 href="#cl::opt">cl::opt</a></tt> class, only the last value will be retained.<p>
1044 <!-- _______________________________________________________________________ -->
1045 </ul><a name="valrequired"><h4><hr size=0>Controlling whether or not a value must be specified</h4><ul>
1047 This group of options is used to control whether or not the option allows a
1048 value to be present. In the case of the CommandLine library, a value is either
1049 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1050 string (e.g. '<tt>-o a.out</tt>').<p>
1052 The allowed values for this option group are:<p>
1055 <a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b> modifier
1056 (which is the default for <tt>bool</tt> typed options) specifies that it is
1057 acceptable to have a value, or not. A boolean argument can be enabled just by
1058 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1059 If an option is specified with this mode, it is illegal for the value to be
1060 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1061 get this behavior, you must use the <a
1062 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.<p>
1064 <a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b> modifier
1065 (which is the default for all other types except for <a
1066 href="#onealternative">unnamed alternatives using the generic parser</a>)
1067 specifies that a value must be provided. This mode informs the command line
1068 library that if an option is not provides with an equal sign, that the next
1069 argument provided must be the value. This allows things like '<tt>-o
1070 a.out</tt>' to work.<p>
1072 <a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b> modifier
1073 (which is the default for <a href="#onealternative">unnamed alternatives using
1074 the generic parser</a>) indicates that it is a runtime error for the user to specify a value. This can be provided to disallow users from providing options to boolean options (like '<tt>-foo=true</tt>').<p>
1078 In general, the default values for this option group work just like you would
1079 want them to. As mentioned above, you can specify the <a
1080 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1081 argument to restrict your command line parser. These options are mostly useful
1082 when <a href="#extensionguide">extending the library</a>.<p>
1086 <!-- _______________________________________________________________________ -->
1087 </ul><a name="formatting"><h4><hr size=0>Controlling other formatting options</h4><ul>
1089 The formatting option group is used to specify that the command line option has
1090 special abilities and is otherwise different from other command line arguments.
1091 As usual, you can only specify at most one of these arguments.<p>
1094 <a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b> modifier
1095 (which is the default all options) specifies that this option is "normal".<p>
1097 <a name="cl::Positional">The <b><tt>cl::Positional</tt></b> modifier specifies
1098 that this is a positional argument, that does not have a command line option
1099 associated with it. See the <a href="#positional">Positional Arguments</a>
1100 section for more information.<p>
1102 The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1103 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.<p>
1106 <a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b> modifier specifies that this
1107 option prefixes its value. With 'Prefix' options, there is no equal sign that
1108 seperates the value from the option name specified. This is useful for
1109 processing odd arguments like '<tt>-lmalloc -L/usr/lib'</tt> in a linker tool.
1110 Here, the '<tt>l</tt>' and '<tt>L</tt>' options are normal string (list)
1111 options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
1112 allow the CommandLine library to recognize them. Note that <a
1113 href="#cl::Prefix">cl::Prefix</a> options must not have the <a
1114 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.<p>
1116 <a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b> modifier is used to
1117 implement unix style tools (like <tt>ls</tt>) that have lots of single letter
1118 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1119 command actually enables four different options, all of which are single
1120 letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
1125 The CommandLine library does not restrict how you use the <a
1126 href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
1127 modifiers, but it is possible to specify ambiguous argument settings. Thus, it
1128 is possible to have multiple letter options that are prefix or grouping options,
1129 and they will still work as designed.<p>
1131 To do this, the CommandLine library uses a greedy algorithm to parse the input
1132 option into (potentially multiple) prefix and grouping options. The strategy
1133 basically looks like this:<p>
1135 <tt>parse(string OrigInput) {</tt>
1137 <li><tt>string input = OrigInput;</tt>
1138 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1139 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1140 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1141 <li><tt>if (getOption(input).isPrefix())<br>
1142 return getOption(input).parse(input);</tt>
1143 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1144 getOption(input).parse();<br>
1145 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1146 input = OrigInput;<br>
1147 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1149 <li><tt>if (!OrigInput.empty()) error();</tt>
1156 <!-- ======================================================================= -->
1157 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
1158 <a name="toplevel">Top-Level Classes and Functions
1159 </b></font></td></tr></table><ul>
1161 Despite all of the builtin flexibility, the CommandLine option library really
1162 only consists of one function (<a
1163 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1164 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1165 href="#cl::list"><tt>cl::list</tt></a>, and <a
1166 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1167 classes in detail.<p>
1169 <!-- _______________________________________________________________________ -->
1170 </ul><a name="cl::ParseCommandLineOptions"><h4><hr size=0>The
1171 <tt>cl::ParseCommandLineOptions</tt> function</h4><ul>
1173 The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1174 directly from <tt>main</tt>, and is used to fill in the values of all of the
1175 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1178 The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1179 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1180 which holds <a href="#description">additional extra text</a> to emit when the
1181 <tt>--help</tt> option is invoked.<p>
1184 <!-- _______________________________________________________________________ -->
1185 </ul><a name="cl::opt"><h4><hr size=0>The <tt>cl::opt</tt> class</h4><ul>
1187 The <tt>cl::opt</tt> class is the class used to represent scalar command line
1188 options, and is the one used most of the time. It is a templated class which
1189 can take up to three arguments (all except for the first have default values
1193 <b>namespace</b> cl {
1194 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1195 <b>class</b> ParserClass = parser<DataType> >
1200 The first template argument specifies what underlying data type the command line
1201 argument is, and is used to select a default parser implementation. The second
1202 template argument is used to specify whether the option should contain the
1203 storage for the option (the default) or whether external storage should be used
1204 to contain the value parsed for the option (see <a href="#storage">Internal vs
1205 External Storage</a> for more information).<p>
1207 The third template argument specifies which parser to use. The default value
1208 selects an instantiation of the <tt>parser</tt> class based on the underlying
1209 data type of the option. In general, this default works well for most
1210 applications, so this option is only used when using a <a
1211 href="#customparser">custom parser</a>.<p>
1214 <!-- _______________________________________________________________________ -->
1215 </ul><a name="cl::list"><h4><hr size=0>The <tt>cl::list</tt> class</h4><ul>
1217 The <tt>cl::list</tt> class is the class used to represent a list of command
1218 line options. It too is a templated class which can take up to three
1222 <b>namespace</b> cl {
1223 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1224 <b>class</b> ParserClass = parser<DataType> >
1229 This class works the exact same as the <a href="#cl::opt"><tt>cl::opt</tt></a>
1230 class, except that the second argument is the <b>type</b> of the external
1231 storage, not a boolean value. For this class, the marker type '<tt>bool</tt>'
1232 is used to indicate that internal storage should be used.<p>
1235 <!-- _______________________________________________________________________ -->
1236 </ul><a name="cl::alias"><h4><hr size=0>The <tt>cl::alias</tt> class</h4><ul>
1238 The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1239 aliases for other arguments.<p>
1242 <b>namespace</b> cl {
1247 The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be used
1248 to specify which option this is an alias for. Alias arguments default to being
1249 <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do the
1250 conversion from string to data.<p>
1253 <!-- ======================================================================= -->
1254 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
1255 <a name="builtinparsers">Builtin parsers
1256 </b></font></td></tr></table><ul>
1258 Parsers control how the string value taken from the command line is translated
1259 into a typed value, suitable for use in a C++ program. By default, the
1260 CommandLine library uses an instance of <tt>parser<type></tt> if the
1261 command line option specifies that it uses values of type '<tt>type</tt>'.
1262 Because of this, custom option processing is specified with specializations of
1263 the '<tt>parser</tt>' class.<p>
1265 The CommandLine library provides the following builtin parser specializations,
1266 which are sufficient for most applications. It can, however, also be extended to
1267 work with new data types and new ways of interpreting the same data. See the <a
1268 href="#customparser">Writing a Custom Parser</a> for more details on this type
1269 of library extension.<p>
1271 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b>
1272 can be used to map strings values to any data type, through the use of the <a
1273 href="#cl::values">cl::values</a> property, which specifies the mapping
1274 information. The most common use of this parser is for parsing enum values,
1275 which allows you to use the CommandLine library for all of the error checking to
1276 make sure that only valid enum values are specified (as opposed to accepting
1277 arbitrary strings). Despite this, however, the generic parser class can be used
1278 for any data type.<p>
1280 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b>
1281 is used to convert boolean strings to a boolean value. Currently accepted
1282 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1283 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".<p>
1285 <li><a name="stringparser">The <b><tt>parser<string></tt> specialization</b> simply stores the parsed string into the string value specified. No conversion or modification of the data is performed.<p>
1287 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b>
1288 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1289 accept a decimal number (with an optional '+' or '-' prefix) which must start
1290 with a non-zero digit. It accepts octal numbers, which are identified with a
1291 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1292 '<tt>0x</tt>' or '<tt>0X</tt>'.<p>
1294 <li><a name="doubleparser">The <b><tt>parser<double></tt></b> and
1295 <b><tt>parser<float></tt> specializations</b> use the standard C
1296 <tt>strtod</tt> function to convert floating point strings into floating point
1297 values. As such, a broad range of string formats is supported, including
1298 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1303 <!-- *********************************************************************** -->
1304 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
1305 <a name="extensionguide">Extension Guide
1306 </b></font></td></tr></table><ul>
1307 <!-- *********************************************************************** -->
1309 Although the CommandLine library has a lot of functionality built into it
1310 already (as discussed previously), one of its true strengths lie in its
1311 extensibility. This section discusses how the CommandLine library works under
1312 the covers and illustrates how to do some simple, common, extensions.<p>
1315 <!-- ======================================================================= -->
1316 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
1317 <tr><td> </td><td width="100%"> <font color="#EEEEFF"
1318 face="Georgia,Palatino"><b> <a name="customparser">Writing a custom parser
1319 </b></font></td></tr></table><ul>
1321 One of the simplest and most common extensions is the use of a custom parser.
1322 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1323 of the CommandLine library that turns string input from the user into a
1324 particular parsed data type, validating the input in the process.<p>
1326 There are two ways to use a new parser:<p>
1329 <li>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1330 your custom data type.<p>
1332 This approach has the advantage that users of your custom data type will
1333 automatically use your custom parser whenever they define an option with a
1334 value type of your data type. The disadvantage of this approach is that it
1335 doesn't work if your fundemental data type is something that is already
1338 <li>Write an independant class, using it explicitly from options that need
1341 This approach works well in situations where you would line to parse an
1342 option using special syntax for a not-very-special data-type. The drawback
1343 of this approach is that users of your parser have to be aware that they are
1344 using your parser, instead of the builtin ones.<p>
1348 To guide the discussion, we will discuss a custom parser that accepts file
1349 sizes, specified with an optional unit after the numeric size. For example, we
1350 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1351 this case, the underlying data type we want to parse into is
1352 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1353 this the default for all <tt>unsigned</tt> options.<p>
1355 To start out, we declare our new <tt>FileSizeParser</tt> class:<p>
1358 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1359 <i>// parse - Return true on error.</i>
1360 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1361 <b>unsigned</b> &Val);
1365 Our new class inherits from the <tt>cl::basic_parser</tt> template class to fill
1366 in the default, boiler plate, code for us. We give it the data type that we
1367 parse into (the last argument to the <tt>parse</tt> method so that clients of
1368 our custom parser know what object type to pass in to the parse method (here we
1369 declare that we parse into '<tt>unsigned</tt>' variables.<p>
1371 For most purposes, the only method that must be implemented in a custom parser
1372 is the <tt>parse</tt> method. The <tt>parse</tt> method is called whenever the
1373 option is invoked, passing in the option itself, the option name, the string to
1374 parse, and a reference to a return value. If the string to parse is not well formed, the parser should output an error message and return true. Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In our example, we implement <tt>parse</tt> as:<p>
1377 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1378 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1379 <b>const char</b> *ArgStart = Arg.c_str();
1382 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1383 Val = (unsigned)strtol(ArgStart, &End, 0);
1386 <b>switch</b> (*End++) {
1387 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1388 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1389 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1392 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1393 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1394 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1397 <i>// Print an error message if unrecognized character!</i>
1398 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1404 This function implements a very simple parser for the kinds of strings we are
1405 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1406 example), it is good enough for this example. Note that we use the option
1407 itself to print out the error message (the <tt>error</tt> method always returns
1408 true) in order to get a nice error message (shown below). Now that we have our
1409 parser class, we can use it like this:<p>
1412 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1413 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1414 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1417 Which adds this to the output of our program:<p>
1421 -help - display available options (--help-hidden for more)
1423 <b>-max-file-size=<size> - Maximum file size to accept</b>
1426 And we can test that our parse works correctly now (the test program just prints
1427 out the max-file-size argument value):<p>
1432 $ ./test -max-file-size=123MB
1434 $ ./test -max-file-size=3G
1436 $ ./test -max-file-size=dog
1437 -max-file-size option: 'dog' value invalid for file size argument!
1440 It looks like it works. The error message that we get is nice and helpful, and
1441 we seem to accept reasonable file sizes. This wraps up the "custom parser"
1445 <!-- ======================================================================= -->
1446 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
1447 <tr><td> </td><td width="100%"> <font color="#EEEEFF"
1448 face="Georgia,Palatino"><b> <a name="explotingexternal">Exploiting external
1449 storage </b></font></td></tr></table><ul>
1453 <!-- ======================================================================= -->
1454 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
1455 <tr><td> </td><td width="100%"> <font color="#EEEEFF"
1456 face="Georgia,Palatino"><b> <a name="dynamicopts">Dynamically adding command
1457 line options </b></font></td></tr></table><ul>
1463 <!-- *********************************************************************** -->
1465 <!-- *********************************************************************** -->
1469 <address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
1470 <!-- Created: Tue Jan 23 15:19:28 CST 2001 -->
1471 <!-- hhmts start -->
1472 Last modified: Wed Aug 7 13:22:40 CDT 2002