1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
6 <title>CommandLine 2.0 Library Manual</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
11 <div class="doc_title">
12 CommandLine 2.0 Library Manual
16 <li><a href="#introduction">Introduction</a></li>
18 <li><a href="#quickstart">Quick Start Guide</a>
20 <li><a href="#bool">Boolean Arguments</a></li>
21 <li><a href="#alias">Argument Aliases</a></li>
22 <li><a href="#onealternative">Selecting an alternative from a
23 set of possibilities</a></li>
24 <li><a href="#namedalternatives">Named alternatives</a></li>
25 <li><a href="#list">Parsing a list of options</a></li>
26 <li><a href="#description">Adding freeform text to help output</a></li>
29 <li><a href="#referenceguide">Reference Guide</a>
31 <li><a href="#positional">Positional Arguments</a>
33 <li><a href="#--">Specifying positional options with hyphens</a></li>
34 <li><a href="#getPosition">Determining absolute position with
36 <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
40 <li><a href="#storage">Internal vs External Storage</a></li>
42 <li><a href="#attributes">Option Attributes</a></li>
44 <li><a href="#modifiers">Option Modifiers</a>
46 <li><a href="#hiding">Hiding an option from <tt>--help</tt>
48 <li><a href="#numoccurrences">Controlling the number of occurrences
49 required and allowed</a></li>
50 <li><a href="#valrequired">Controlling whether or not a value must be
52 <li><a href="#formatting">Controlling other formatting options</a></li>
53 <li><a href="#misc">Miscellaneous option modifiers</a></li>
56 <li><a href="#toplevel">Top-Level Classes and Functions</a>
58 <li><a href="#cl::ParseCommandLineOptions">The
59 <tt>cl::ParseCommandLineOptions</tt> function</a></li>
60 <li><a href="#cl::ParseEnvironmentOptions">The
61 <tt>cl::ParseEnvironmentOptions</tt> function</a></li>
62 <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li>
63 <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li>
64 <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li>
65 <li><a href="#cl::extrahelp">The <tt>cl::extrahelp</tt> class</a></li>
68 <li><a href="#builtinparsers">Builtin parsers</a>
70 <li><a href="#genericparser">The Generic <tt>parser<t></tt>
72 <li><a href="#boolparser">The <tt>parser<bool></tt>
73 specialization</a></li>
74 <li><a href="#stringparser">The <tt>parser<string></tt>
75 specialization</a></li>
76 <li><a href="#intparser">The <tt>parser<int></tt>
77 specialization</a></li>
78 <li><a href="#doubleparser">The <tt>parser<double></tt> and
79 <tt>parser<float></tt> specializations</a></li>
82 <li><a href="#extensionguide">Extension Guide</a>
84 <li><a href="#customparser">Writing a custom parser</a></li>
85 <li><a href="#explotingexternal">Exploiting external storage</a></li>
86 <li><a href="#dynamicopts">Dynamically adding command line
91 <div class="doc_author">
92 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
95 <!-- *********************************************************************** -->
96 <div class="doc_section">
97 <a name="introduction">Introduction</a>
99 <!-- *********************************************************************** -->
101 <div class="doc_text">
103 <p>This document describes the CommandLine argument processing library. It will
104 show you how to use it, and what it can do. The CommandLine library uses a
105 declarative approach to specifying the command line options that your program
106 takes. By default, these options declarations implicitly hold the value parsed
107 for the option declared (of course this <a href="#storage">can be
110 <p>Although there are a <b>lot</b> of command line argument parsing libraries
111 out there in many different languages, none of them fit well with what I needed.
112 By looking at the features and problems of other libraries, I designed the
113 CommandLine library to have the following features:</p>
116 <li>Speed: The CommandLine library is very quick and uses little resources. The
117 parsing time of the library is directly proportional to the number of arguments
118 parsed, not the the number of options recognized. Additionally, command line
119 argument values are captured transparently into user defined global variables,
120 which can be accessed like any other variable (and with the same
123 <li>Type Safe: As a user of CommandLine, you don't have to worry about
124 remembering the type of arguments that you want (is it an int? a string? a
125 bool? an enum?) and keep casting it around. Not only does this help prevent
126 error prone constructs, it also leads to dramatically cleaner source code.</li>
128 <li>No subclasses required: To use CommandLine, you instantiate variables that
129 correspond to the arguments that you would like to capture, you don't subclass a
130 parser. This means that you don't have to write <b>any</b> boilerplate
133 <li>Globally accessible: Libraries can specify command line arguments that are
134 automatically enabled in any tool that links to the library. This is possible
135 because the application doesn't have to keep a "list" of arguments to pass to
136 the parser. This also makes supporting <a href="#dynamicopts">dynamically
137 loaded options</a> trivial.</li>
139 <li>Cleaner: CommandLine supports enum and other types directly, meaning that
140 there is less error and more security built into the library. You don't have to
141 worry about whether your integral command line argument accidentally got
142 assigned a value that is not valid for your enum type.</li>
144 <li>Powerful: The CommandLine library supports many different types of
145 arguments, from simple <a href="#boolparser">boolean flags</a> to <a
146 href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
147 href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
148 href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
149 arguments</a>. This is possible because CommandLine is...</li>
151 <li>Extensible: It is very simple to add a new argument type to CommandLine.
152 Simply specify the parser that you want to use with the command line option when
153 you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li>
155 <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
156 that you, the user, have to do. For example, it automatically provides a
157 <tt>--help</tt> option that shows the available command line options for your
158 tool. Additionally, it does most of the basic correctness checking for
161 <li>Capable: The CommandLine library can handle lots of different forms of
162 options often found in real programs. For example, <a
163 href="#positional">positional</a> arguments, <tt>ls</tt> style <a
164 href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
165 -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
166 options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
167 href="#cl::ConsumeAfter">interpreter style options</a>.</li>
171 <p>This document will hopefully let you jump in and start using CommandLine in
172 your utility quickly and painlessly. Additionally it should be a simple
173 reference manual to figure out how stuff works. If it is failing in some area
174 (or you want an extension to the library), nag the author, <a
175 href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
179 <!-- *********************************************************************** -->
180 <div class="doc_section">
181 <a name="quickstart">Quick Start Guide</a>
183 <!-- *********************************************************************** -->
185 <div class="doc_text">
187 <p>This section of the manual runs through a simple CommandLine'ification of a
188 basic compiler tool. This is intended to show you how to jump into using the
189 CommandLine library in your own program, and show you some of the cool things it
192 <p>To start out, you need to include the CommandLine header file into your
195 <div class="doc_code"><pre>
196 #include "Support/CommandLine.h"
199 <p>Additionally, you need to add this as the first line of your main
202 <div class="doc_code"><pre>
203 int main(int argc, char **argv) {
204 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
209 <p>... which actually parses the arguments and fills in the variable
212 <p>Now that you are ready to support command line arguments, we need to tell the
213 system which ones we want, and what type of argument they are. The CommandLine
214 library uses a declarative syntax to model command line arguments with the
215 global variable declarations that capture the parsed values. This means that
216 for every command line option that you would like to support, there should be a
217 global variable declaration to capture the result. For example, in a compiler,
218 we would like to support the unix standard '<tt>-o <filename></tt>' option
219 to specify where to put the output. With the CommandLine library, this is
220 represented like this:</p>
222 <a name="value_desc_example"></a>
223 <div class="doc_code"><pre>
224 <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>"));
227 <p>This declares a global variable "<tt>OutputFilename</tt>" that is used to
228 capture the result of the "<tt>o</tt>" argument (first parameter). We specify
229 that this is a simple scalar option by using the "<tt><a
230 href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a
231 href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library
232 that the data type that we are parsing is a string.</p>
234 <p>The second and third parameters (which are optional) are used to specify what
235 to output for the "<tt>--help</tt>" option. In this case, we get a line that
238 <div class="doc_code"><pre>
239 USAGE: compiler [options]
242 -help - display available options (--help-hidden for more)
243 <b>-o <filename> - Specify output filename</b>
246 <p>Because we specified that the command line option should parse using the
247 <tt>string</tt> data type, the variable declared is automatically usable as a
248 real string in all contexts that a normal C++ string object may be used. For
251 <div class="doc_code"><pre>
253 ofstream Output(OutputFilename.c_str());
258 <p>There are many different options that you can use to customize the command
259 line option handling library, but the above example shows the general interface
260 to these options. The options can be specified in any order, and are specified
261 with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
262 there are no positional dependencies to remember. The available options are
263 discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p>
265 <p>Continuing the example, we would like to have our compiler take an input
266 filename as well as an output filename, but we do not want the input filename to
267 be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
268 style of argument, the CommandLine library allows for <a
269 href="#positional">positional</a> arguments to be specified for the program.
270 These positional arguments are filled with command line parameters that are not
271 in option form. We use this feature like this:</p>
273 <div class="doc_code"><pre>
274 <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>"));
277 <p>This declaration indicates that the first positional argument should be
278 treated as the input filename. Here we use the <tt><a
279 href="#cl::init">cl::init</a></tt> option to specify an initial value for the
280 command line option, which is used if the option is not specified (if you do not
281 specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
282 the default constructor for the data type is used to initialize the value).
283 Command line options default to being optional, so if we would like to require
284 that the user always specify an input filename, we would add the <tt><a
285 href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
286 <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p>
288 <div class="doc_code"><pre>
289 <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>);
292 <p>Again, the CommandLine library does not require the options to be specified
293 in any particular order, so the above declaration is equivalent to:</p>
295 <div class="doc_code"><pre>
296 <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>"));
299 <p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag,
300 the CommandLine library will automatically issue an error if the argument is not
301 specified, which shifts all of the command line option verification code out of
302 your application into the library. This is just one example of how using flags
303 can alter the default behaviour of the library, on a per-option basis. By
304 adding one of the declarations above, the <tt>--help</tt> option synopsis is now
307 <div class="doc_code"><pre>
308 USAGE: compiler [options] <b><input file></b>
311 -help - display available options (--help-hidden for more)
312 -o <filename> - Specify output filename
315 <p>... indicating that an input filename is expected.</p>
319 <!-- ======================================================================= -->
320 <div class="doc_subsection">
321 <a name="bool">Boolean Arguments</a>
324 <div class="doc_text">
326 <p>In addition to input and output filenames, we would like the compiler example
327 to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
328 file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
329 compatibility with some of our users. We can support these by declaring options
330 of boolean type like this:</p>
332 <div class="doc_code"><pre>
333 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
334 <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>"));
335 <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>);
338 <p>This does what you would expect: it declares three boolean variables
339 ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
340 options. Note that the "<tt>-q</tt>" option is specified with the "<a
341 href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
342 from being shown by the standard "<tt>--help</tt>" output (note that it is still
343 shown in the "<tt>--help-hidden</tt>" output).</p>
345 <p>The CommandLine library uses a <a href="#builtinparsers">different parser</a>
346 for different data types. For example, in the string case, the argument passed
347 to the option is copied literally into the content of the string variable... we
348 obviously cannot do that in the boolean case, however, so we must use a smarter
349 parser. In the case of the boolean parser, it allows no options (in which case
350 it assigns the value of true to the variable), or it allows the values
351 "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
352 following inputs:</p>
354 <div class="doc_code"><pre>
355 compiler -f # No value, 'Force' == true
356 compiler -f=true # Value specified, 'Force' == true
357 compiler -f=TRUE # Value specified, 'Force' == true
358 compiler -f=FALSE # Value specified, 'Force' == false
361 <p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns
362 the string values into boolean values, and rejects things like '<tt>compiler
363 -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
364 href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
365 like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
366 library calls to parse the string value into the specified data type.</p>
368 <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
370 <div class="doc_code"><pre>
371 USAGE: compiler [options] <input file>
374 <b>-f - Overwrite output files</b>
375 -o - Override output filename
376 <b>-quiet - Don't print informational messages</b>
377 -help - display available options (--help-hidden for more)
380 <p>and "<tt>opt --help-hidden</tt>" prints this:</p>
382 <div class="doc_code"><pre>
383 USAGE: compiler [options] <input file>
386 -f - Overwrite output files
387 -o - Override output filename
388 <b>-q - Don't print informational messages</b>
389 -quiet - Don't print informational messages
390 -help - display available options (--help-hidden for more)
393 <p>This brief example has shown you how to use the '<tt><a
394 href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
395 arguments. In addition to simple scalar arguments, the CommandLine library also
396 provides primitives to support CommandLine option <a href="#alias">aliases</a>,
397 and <a href="#list">lists</a> of options.</p>
401 <!-- ======================================================================= -->
402 <div class="doc_subsection">
403 <a name="alias">Argument Aliases</a>
406 <div class="doc_text">
408 <p>So far, the example works well, except for the fact that we need to check the
409 quiet condition like this now:</p>
411 <div class="doc_code"><pre>
413 if (!Quiet && !Quiet2) printInformationalMessage(...);
417 <p>... which is a real pain! Instead of defining two values for the same
418 condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
419 option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
422 <div class="doc_code"><pre>
423 <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
424 <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>"));
425 <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));
428 <p>The third line (which is the only one we modified from above) defines a
429 "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by
430 the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
431 specified. Because aliases do not hold state, the only thing the program has to
432 query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
433 that they automatically hide themselves from the <tt>-help</tt> output
434 (although, again, they are still visible in the <tt>--help-hidden
437 <p>Now the application code can simply use:</p>
439 <div class="doc_code"><pre>
441 if (!Quiet) printInformationalMessage(...);
445 <p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>"
446 can be used to specify an alternative name for any variable type, and has many
451 <!-- ======================================================================= -->
452 <div class="doc_subsection">
453 <a name="onealternative">Selecting an alternative from a set of
457 <div class="doc_text">
459 <p>So far, we have seen how the CommandLine library handles builtin types like
460 <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
461 things it doesn't know about, like enums or '<tt>int*</tt>'s?</p>
463 <p>The answer is that it uses a table driven generic parser (unless you specify
464 your own parser, as described in the <a href="#extensionguide">Extension
465 Guide</a>). This parser maps literal strings to whatever type is required, and
466 requires you to tell it what this mapping should be.</p>
468 <p>Lets say that we would like to add four optimization levels to our
469 optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>",
470 "<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean
471 options like above, but there are several problems with this strategy:</p>
474 <li>A user could specify more than one of the options at a time, for example,
475 "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this
476 erroneous input for us.</li>
478 <li>We would have to test 4 different variables to see which ones are set.</li>
480 <li>This doesn't map to the numeric levels that we want... so we cannot easily
481 see if some level >= "<tt>-O1</tt>" is enabled.</li>
485 <p>To cope with these problems, we can use an enum value, and have the
486 CommandLine library fill it in with the appropriate level directly, which is
489 <div class="doc_code"><pre>
494 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
495 <a href="#cl::values">cl::values</a>(
496 clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
497 clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
498 clEnumVal(O2, "<i>Enable default optimizations</i>"),
499 clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
503 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
507 <p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
508 "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
509 that are listed in the declaration (Note that the declaration list must be
510 terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine
512 that the user can only specify one of the options, and it ensure that only valid
513 enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
514 command line arguments matched the enum values. With this option added, our
515 help output now is:</p>
517 <div class="doc_code"><pre>
518 USAGE: compiler [options] <input file>
521 <b>Choose optimization level:
522 -g - No optimizations, enable debugging
523 -O1 - Enable trivial optimizations
524 -O2 - Enable default optimizations
525 -O3 - Enable expensive optimizations</b>
526 -f - Overwrite output files
527 -help - display available options (--help-hidden for more)
528 -o <filename> - Specify output filename
529 -quiet - Don't print informational messages
532 <p>In this case, it is sort of awkward that flag names correspond directly to
533 enum names, because we probably don't want a enum definition named "<tt>g</tt>"
534 in our program. Because of this, we can alternatively write this example like
537 <div class="doc_code"><pre>
542 <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
543 <a href="#cl::values">cl::values</a>(
544 clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
545 clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
546 clEnumVal(O2 , "<i>Enable default optimizations</i>"),
547 clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
551 if (OptimizationLevel == Debug) outputDebugInfo(...);
555 <p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we
556 can directly specify the name that the flag should get. In general a direct
557 mapping is nice, but sometimes you can't or don't want to preserve the mapping,
558 which is when you would use it.</p>
562 <!-- ======================================================================= -->
563 <div class="doc_subsection">
564 <a name="namedalternatives">Named Alternatives</a>
567 <div class="doc_text">
569 <p>Another useful argument form is a named alternative style. We shall use this
570 style in our compiler to specify different debug levels that can be used.
571 Instead of each debug level being its own switch, we want to support the
572 following options, of which only one can be specified at a time:
573 "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
574 "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
575 our optimization level flags, but we also specify an option name. For this
576 case, the code looks like this:</p>
578 <div class="doc_code"><pre>
580 nodebuginfo, quick, detailed
583 // Enable Debug Options to be specified on the command line
584 <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>"),
585 <a href="#cl::values">cl::values</a>(
586 clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
587 clEnumVal(quick, "<i>enable quick debug information</i>"),
588 clEnumVal(detailed, "<i>enable detailed debug information</i>"),
592 <p>This definition defines an enumerated command line variable of type "<tt>enum
593 DebugLev</tt>", which works exactly the same way as before. The difference here
594 is just the interface exposed to the user of your program and the help output by
595 the "<tt>--help</tt>" option:</p>
597 <div class="doc_code"><pre>
598 USAGE: compiler [options] <input file>
601 Choose optimization level:
602 -g - No optimizations, enable debugging
603 -O1 - Enable trivial optimizations
604 -O2 - Enable default optimizations
605 -O3 - Enable expensive optimizations
606 <b>-debug_level - Set the debugging level:
607 =none - disable debug information
608 =quick - enable quick debug information
609 =detailed - enable detailed debug information</b>
610 -f - Overwrite output files
611 -help - display available options (--help-hidden for more)
612 -o <filename> - Specify output filename
613 -quiet - Don't print informational messages
616 <p>Again, the only structural difference between the debug level declaration and
617 the optimization level declaration is that the debug level declaration includes
618 an option name (<tt>"debug_level"</tt>), which automatically changes how the
619 library processes the argument. The CommandLine library supports both forms so
620 that you can choose the form most appropriate for your application.</p>
624 <!-- ======================================================================= -->
625 <div class="doc_subsection">
626 <a name="list">Parsing a list of options</a>
629 <div class="doc_text">
631 <p>Now that we have the standard run of the mill argument types out of the way,
632 lets get a little wild and crazy. Lets say that we want our optimizer to accept
633 a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
634 might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
635 this case, the order of the arguments and the number of appearances is very
636 important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
637 template is for. First, start by defining an enum of the optimizations that you
638 would like to perform:</p>
640 <div class="doc_code"><pre>
642 // 'inline' is a C++ keyword, so name it 'inlining'
643 dce, constprop, inlining, strip
647 <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
649 <div class="doc_code"><pre>
650 <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
651 <a href="#cl::values">cl::values</a>(
652 clEnumVal(dce , "<i>Dead Code Elimination</i>"),
653 clEnumVal(constprop , "<i>Constant Propagation</i>"),
654 clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
655 clEnumVal(strip , "<i>Strip Symbols</i>"),
659 <p>This defines a variable that is conceptually of the type
660 "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
663 <div class="doc_code"><pre>
664 for (unsigned i = 0; i != OptimizationList.size(); ++i)
665 switch (OptimizationList[i])
669 <p>... to iterate through the list of options specified.</p>
671 <p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is
672 completely general and may be used with any data types or other arguments that
673 you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One
674 especially useful way to use a list is to capture all of the positional
675 arguments together if there may be more than one specified. In the case of a
676 linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to
677 capture them into a list. This is naturally specified as:</p>
679 <div class="doc_code"><pre>
681 <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>);
685 <p>This variable works just like a "<tt>vector<string></tt>" object. As
686 such, accessing the list is simple, just like above. In this example, we used
687 the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
688 CommandLine library that it is an error if the user does not specify any
689 <tt>.o</tt> files on our command line. Again, this just reduces the amount of
690 checking we have to do.</p>
694 <!-- ======================================================================= -->
695 <div class="doc_subsection">
696 <a name="description">Adding freeform text to help output</a>
699 <div class="doc_text">
701 <p>As our program grows and becomes more mature, we may decide to put summary
702 information about what it does into the help output. The help output is styled
703 to look similar to a Unix <tt>man</tt> page, providing concise information about
704 a program. Unix <tt>man</tt> pages, however often have a description about what
705 the program does. To add this to your CommandLine program, simply pass a third
707 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
708 call in main. This additional argument is then printed as the overview
709 information for your program, allowing you to include any additional information
710 that you want. For example:</p>
712 <div class="doc_code"><pre>
713 int main(int argc, char **argv) {
714 <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
715 " This program blah blah blah...\n");
720 <p>would yield the help output:</p>
722 <div class="doc_code"><pre>
723 <b>OVERVIEW: CommandLine compiler example
725 This program blah blah blah...</b>
727 USAGE: compiler [options] <input file>
731 -help - display available options (--help-hidden for more)
732 -o <filename> - Specify output filename
738 <!-- *********************************************************************** -->
739 <div class="doc_section">
740 <a name="referenceguide">Reference Guide</a>
742 <!-- *********************************************************************** -->
744 <div class="doc_text">
746 <p>Now that you know the basics of how to use the CommandLine library, this
747 section will give you the detailed information you need to tune how command line
748 options work, as well as information on more "advanced" command line option
749 processing capabilities.</p>
753 <!-- ======================================================================= -->
754 <div class="doc_subsection">
755 <a name="positional">Positional Arguments</a>
758 <div class="doc_text">
760 <p>Positional arguments are those arguments that are not named, and are not
761 specified with a hyphen. Positional arguments should be used when an option is
762 specified by its position alone. For example, the standard Unix <tt>grep</tt>
763 tool takes a regular expression argument, and an optional filename to search
764 through (which defaults to standard input if a filename is not specified).
765 Using the CommandLine library, this would be specified as:</p>
767 <div class="doc_code"><pre>
768 <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>);
769 <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>"));
772 <p>Given these two option declarations, the <tt>--help</tt> output for our grep
773 replacement would look like this:</p>
775 <div class="doc_code"><pre>
776 USAGE: spiffygrep [options] <b><regular expression> <input file></b>
779 -help - display available options (--help-hidden for more)
782 <p>... and the resultant program could be used just like the standard
783 <tt>grep</tt> tool.</p>
785 <p>Positional arguments are sorted by their order of construction. This means
786 that command line options will be ordered according to how they are listed in a
787 .cpp file, but will not have an ordering defined if the positional arguments
788 are defined in multiple .cpp files. The fix for this problem is simply to
789 define all of your positional arguments in one .cpp file.</p>
794 <!-- _______________________________________________________________________ -->
795 <div class="doc_subsubsection">
796 <a name="--">Specifying positional options with hyphens</a>
799 <div class="doc_text">
801 <p>Sometimes you may want to specify a value to your positional argument that
802 starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
803 first, you will have trouble doing this, because it will try to find an argument
804 named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
805 Note that the system <tt>grep</tt> has the same problem:</p>
807 <div class="doc_code"><pre>
808 $ spiffygrep '-foo' test.txt
809 Unknown command line argument '-foo'. Try: spiffygrep --help'
811 $ grep '-foo' test.txt
812 grep: illegal option -- f
813 grep: illegal option -- o
814 grep: illegal option -- o
815 Usage: grep -hblcnsviw pattern file . . .
818 <p>The solution for this problem is the same for both your tool and the system
819 version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
820 the command line, it is telling the program that all options after the
821 '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
822 can use it like this:</p>
824 <div class="doc_code"><pre>
825 $ spiffygrep -- -foo test.txt
831 <!-- _______________________________________________________________________ -->
832 <div class="doc_subsubsection">
833 <a name="getPosition">Determining absolute position with getPosition()</a>
835 <div class="doc_text">
836 <p>Sometimes an option can affect or modify the meaning of another option. For
837 example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells
838 <tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force
839 the file to be interpreted as if it contained source code in language
840 <tt>LANG</tt>. In order to handle this properly , you need to know the
841 absolute position of each argument, especially those in lists, so their
842 interaction(s) can be applied correctly. This is also useful for options like
843 <tt>-llibname</tt> which is actually a positional argument that starts with
845 <p>So, generally, the problem is that you have two <tt>cl::list</tt> variables
846 that interact in some way. To ensure the correct interaction, you can use the
847 <tt>cl::list::getPosition(optnum)</tt> method. This method returns the
848 absolute position (as found on the command line) of the <tt>optnum</tt>
849 item in the <tt>cl::list</tt>.</p>
850 <p>The idiom for usage is like this:</p>
852 <div class="doc_code"><pre>
853 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
854 static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore);
856 int main(int argc, char**argv) {
858 std::vector<std::string>::iterator fileIt = Files.begin();
859 std::vector<std::string>::iterator libIt = Libraries.begin();
860 unsigned libPos = 0, filePos = 0;
862 if ( libIt != Libraries.end() )
863 libPos = Libraries.getPosition( libIt - Libraries.begin() );
866 if ( fileIt != Files.end() )
867 filePos = Files.getPosition( fileIt - Files.begin() );
871 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
872 // Source File Is next
875 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
880 break; // we're done with the list
884 <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an
885 <tt>unsigned getPosition()</tt> option that will provide the absolute position
886 of that option. You can apply the same approach as above with a
887 <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p>
890 <!-- _______________________________________________________________________ -->
891 <div class="doc_subsubsection">
892 <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
895 <div class="doc_text">
897 <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
898 used to construct programs that use "interpreter style" option processing. With
899 this style of option processing, all arguments specified after the last
900 positional argument are treated as special interpreter arguments that are not
901 interpreted by the command line argument.</p>
903 <p>As a concrete example, lets say we are developing a replacement for the
904 standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
905 you specify options to the shell itself (like <tt>-x</tt> which turns on trace
906 output), then you specify the name of the script to run, then you specify
907 arguments to the script. These arguments to the script are parsed by the bourne
908 shell command line option processor, but are not interpreted as options to the
909 shell itself. Using the CommandLine library, we would specify this as:</p>
911 <div class="doc_code"><pre>
912 <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>("-"));
913 <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>"));
914 <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
917 <p>which automatically provides the help output:</p>
919 <div class="doc_code"><pre>
920 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
923 -help - display available options (--help-hidden for more)
924 <b>-x - Enable trace output</b>
927 <p>At runtime, if we run our new shell replacement as `<tt>spiffysh -x test.sh
928 -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
929 <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
930 <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
931 were specified after the last positional argument (which is the script
934 <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
935 be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
936 per program, there must be at least one <a href="#positional">positional
937 argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
938 positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
939 href="#cl::list">cl::list</a> option.</p>
943 <!-- ======================================================================= -->
944 <div class="doc_subsection">
945 <a name="storage">Internal vs External Storage</a>
948 <div class="doc_text">
950 <p>By default, all command line options automatically hold the value that they
951 parse from the command line. This is very convenient in the common case,
952 especially when combined with the ability to define command line options in the
953 files that use them. This is called the internal storage model.</p>
955 <p>Sometimes, however, it is nice to separate the command line option processing
956 code from the storage of the value parsed. For example, lets say that we have a
957 '<tt>-debug</tt>' option that we would like to use to enable debug information
958 across the entire body of our program. In this case, the boolean value
959 controlling the debug code should be globally accessable (in a header file, for
960 example) yet the command line option processing code should not be exposed to
961 all of these clients (requiring lots of .cpp files to #include
962 <tt>CommandLine.h</tt>).</p>
964 <p>To do this, set up your .h file with your option, like this for example:</p>
966 <div class="doc_code">
968 <i>// DebugFlag.h - Get access to the '-debug' command line option
971 // DebugFlag - This boolean is set to true if the '-debug' command line option
972 // is specified. This should probably not be referenced directly, instead, use
973 // the DEBUG macro below.
975 extern bool DebugFlag;
977 <i>// DEBUG macro - This macro should be used by code to emit debug information.
978 // In the '-debug' option is specified on the command line, and if this is a
979 // debug build, then the code specified as the option to the macro will be
980 // executed. Otherwise it will not be. Example:
982 // DEBUG(std::cerr << "Bitset contains: " << Bitset << "\n");
984 <span class="doc_hilite">#ifdef NDEBUG
987 #define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0)
988 <span class="doc_hilite">#endif</span>
992 <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
993 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
994 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
995 an additial argument to our command line argument processor, and we specify
996 where to fill in with the <a href="#cl::location">cl::location</a>
999 <div class="doc_code">
1001 bool DebugFlag; <i>// the actual value</i>
1002 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
1003 Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>, <a href="#cl::location">cl::location</a>(DebugFlag));
1007 <p>In the above example, we specify "<tt>true</tt>" as the second argument to
1008 the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the
1009 template should not maintain a copy of the value itself. In addition to this,
1010 we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so
1011 that <tt>DebugFlag</tt> is automatically set.</p>
1015 <!-- ======================================================================= -->
1016 <div class="doc_subsection">
1017 <a name="attributes">Option Attributes</a>
1020 <div class="doc_text">
1022 <p>This section describes the basic attributes that you can specify on
1027 <li>The option name attribute (which is required for all options, except <a
1028 href="#positional">positional options</a>) specifies what the option name is.
1029 This option is specified in simple double quotes:
1032 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
1037 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
1038 description for the option to be shown in the <tt>--help</tt> output for the
1041 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
1042 specifies a string that can be used to fine tune the <tt>--help</tt> output for
1043 a command line option. Look <a href="#value_desc_example">here</a> for an
1046 <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
1047 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
1048 not specified then the command line option value defaults to the value created
1049 by the default constructor for the type. <b>Warning</b>: If you specify both
1050 <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
1051 you must specify <b><tt>cl::location</tt></b> first, so that when the
1052 command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
1053 initial value. (You will get an error at runtime if you don't put them in
1054 the right order.)</li>
1056 <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
1057 store the value for a parsed command line option if using external storage. See
1058 the section on <a href="#storage">Internal vs External Storage</a> for more
1061 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
1062 specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is
1065 <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
1066 the string-to-value mapping to be used by the generic parser. It takes a
1067 <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
1069 specify the option name, the value mapped to, and the description shown in the
1070 <tt>--help</tt> for the tool. Because the generic parser is used most
1071 frequently with enum values, two macros are often useful:
1075 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
1076 nice simple way to specify a triplet for an enum. This macro automatically
1077 makes the option name be the same as the enum name. The first option to the
1078 macro is the enum, the second is the description for the command line
1081 <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
1082 specify macro options where the option name doesn't equal the enum name. For
1083 this macro, the first argument is the enum value, the second is the flag name,
1084 and the second is the description.</li>
1088 You will get a compile time error if you try to use cl::values with a parser
1089 that does not support it.</li>
1095 <!-- ======================================================================= -->
1096 <div class="doc_subsection">
1097 <a name="modifiers">Option Modifiers</a>
1100 <div class="doc_text">
1102 <p>Option modifiers are the flags and expressions that you pass into the
1103 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1104 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
1105 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
1106 your application well.</p>
1108 <p>These options fall into five main catagories:</p>
1111 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
1112 <li><a href="#numoccurrences">Controlling the number of occurrences
1113 required and allowed</a></li>
1114 <li><a href="#valrequired">Controlling whether or not a value must be
1116 <li><a href="#formatting">Controlling other formatting options</a></li>
1117 <li><a href="#misc">Miscellaneous option modifiers</a></li>
1120 <p>It is not possible to specify two options from the same catagory (you'll get
1121 a runtime error) to a single option, except for options in the miscellaneous
1122 catagory. The CommandLine library specifies defaults for all of these settings
1123 that are the most useful in practice and the most common, which mean that you
1124 usually shouldn't have to worry about these.</p>
1128 <!-- _______________________________________________________________________ -->
1129 <div class="doc_subsubsection">
1130 <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
1133 <div class="doc_text">
1135 <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
1136 <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
1137 appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
1138 compiled program:</p>
1142 <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
1143 (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1144 href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
1145 in both help listings.</li>
1147 <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
1148 default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
1149 the option should not appear in the <tt>--help</tt> output, but should appear in
1150 the <tt>--help-hidden</tt> output.</li>
1152 <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
1153 indicates that the option should not appear in any help output.</li>
1159 <!-- _______________________________________________________________________ -->
1160 <div class="doc_subsubsection">
1161 <a name="numoccurrences">Controlling the number of occurrences required and
1165 <div class="doc_text">
1167 <p>This group of options is used to control how many time an option is allowed
1168 (or required) to be specified on the command line of your program. Specifying a
1169 value for this setting allows the CommandLine library to do error checking for
1172 <p>The allowed values for this option group are:</p>
1176 <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
1177 is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1178 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1179 allow either zero or one occurrence of the option to be specified.</li>
1181 <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
1182 (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
1183 indicates that your program will allow the option to be specified zero or more
1186 <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
1187 indicates that the specified option must be specified exactly one time.</li>
1189 <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
1190 indicates that the option must be specified at least one time.</li>
1192 <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1193 href="#positional">Positional arguments section</a></li>
1197 <p>If an option is not specified, then the value of the option is equal to the
1198 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1199 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1200 option value is initialized with the default constructor for the data type.</p>
1202 <p>If an option is specified multiple times for an option of the <tt><a
1203 href="#cl::opt">cl::opt</a></tt> class, only the last value will be
1208 <!-- _______________________________________________________________________ -->
1209 <div class="doc_subsubsection">
1210 <a name="valrequired">Controlling whether or not a value must be specified</a>
1213 <div class="doc_text">
1215 <p>This group of options is used to control whether or not the option allows a
1216 value to be present. In the case of the CommandLine library, a value is either
1217 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1218 string (e.g. '<tt>-o a.out</tt>').</p>
1220 <p>The allowed values for this option group are:</p>
1224 <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
1225 (which is the default for <tt>bool</tt> typed options) specifies that it is
1226 acceptable to have a value, or not. A boolean argument can be enabled just by
1227 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1228 If an option is specified with this mode, it is illegal for the value to be
1229 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1230 get this behavior, you must use the <a
1231 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
1233 <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
1234 (which is the default for all other types except for <a
1235 href="#onealternative">unnamed alternatives using the generic parser</a>)
1236 specifies that a value must be provided. This mode informs the command line
1237 library that if an option is not provides with an equal sign, that the next
1238 argument provided must be the value. This allows things like '<tt>-o
1239 a.out</tt>' to work.</li>
1241 <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
1242 modifier (which is the default for <a href="#onealternative">unnamed
1243 alternatives using the generic parser</a>) indicates that it is a runtime error
1244 for the user to specify a value. This can be provided to disallow users from
1245 providing options to boolean options (like '<tt>-foo=true</tt>').</li>
1249 <p>In general, the default values for this option group work just like you would
1250 want them to. As mentioned above, you can specify the <a
1251 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1252 argument to restrict your command line parser. These options are mostly useful
1253 when <a href="#extensionguide">extending the library</a>.</p>
1257 <!-- _______________________________________________________________________ -->
1258 <div class="doc_subsubsection">
1259 <a name="formatting">Controlling other formatting options</a>
1262 <div class="doc_text">
1264 <p>The formatting option group is used to specify that the command line option
1265 has special abilities and is otherwise different from other command line
1266 arguments. As usual, you can only specify at most one of these arguments.</p>
1270 <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
1271 modifier (which is the default all options) specifies that this option is
1274 <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
1275 specifies that this is a positional argument, that does not have a command line
1276 option associated with it. See the <a href="#positional">Positional
1277 Arguments</a> section for more information.</li>
1279 <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1280 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
1282 <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
1283 that this option prefixes its value. With 'Prefix' options, the equal sign does
1284 not separate the value from the option name specified. Instead, the value is
1285 everything after the prefix, including any equal sign if present. This is useful
1286 for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a
1287 linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the
1288 '<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list)
1289 options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
1290 allow the CommandLine library to recognize them. Note that
1291 <a href="#cl::Prefix">cl::Prefix</a> options must not have the <a
1292 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li>
1294 <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
1295 to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
1296 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1297 command actually enables four different options, all of which are single
1298 letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
1303 <p>The CommandLine library does not restrict how you use the <a
1304 href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
1305 modifiers, but it is possible to specify ambiguous argument settings. Thus, it
1306 is possible to have multiple letter options that are prefix or grouping options,
1307 and they will still work as designed.</p>
1309 <p>To do this, the CommandLine library uses a greedy algorithm to parse the
1310 input option into (potentially multiple) prefix and grouping options. The
1311 strategy basically looks like this:</p>
1313 <div class="doc_code"><tt>parse(string OrigInput) {</tt>
1316 <li><tt>string input = OrigInput;</tt>
1317 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1318 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1319 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1320 <li><tt>if (getOption(input).isPrefix())<br>
1321 return getOption(input).parse(input);</tt>
1322 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1323 getOption(input).parse();<br>
1324 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1325 input = OrigInput;<br>
1326 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1328 <li><tt>if (!OrigInput.empty()) error();</tt></li>
1336 <!-- _______________________________________________________________________ -->
1337 <div class="doc_subsubsection">
1338 <a name="misc">Miscellaneous option modifiers</a>
1341 <div class="doc_text">
1343 <p>The miscellaneous option modifiers are the only flags where you can specify
1344 more than one flag from the set: they are not mutually exclusive. These flags
1345 specify boolean properties that modify the option.</p>
1349 <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
1350 indicates that any commas specified for an option's value should be used to
1351 split the value up into multiple values for the option. For example, these two
1352 options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
1353 "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
1354 makes sense to be used in a case where the option is allowed to accept one or
1355 more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
1357 <li><a name="cl::PositionalEatsArgs">The
1358 <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
1359 positional arguments, and only makes sense for lists) indicates that positional
1360 argument should consume any strings after it (including strings that start with
1361 a "-") up until another recognized positional argument. For example, if you
1362 have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the
1363 string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
1364 -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
1365 "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
1369 <p>So far, these are the only two miscellaneous option modifiers.</p>
1373 <!-- ======================================================================= -->
1374 <div class="doc_subsection">
1375 <a name="toplevel">Top-Level Classes and Functions</a>
1378 <div class="doc_text">
1380 <p>Despite all of the built-in flexibility, the CommandLine option library
1381 really only consists of one function (<a
1382 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1383 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1384 href="#cl::list"><tt>cl::list</tt></a>, and <a
1385 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1386 classes in detail.</p>
1390 <!-- _______________________________________________________________________ -->
1391 <div class="doc_subsubsection">
1392 <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
1396 <div class="doc_text">
1398 <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1399 directly from <tt>main</tt>, and is used to fill in the values of all of the
1400 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1403 <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1404 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1405 which holds <a href="#description">additional extra text</a> to emit when the
1406 <tt>--help</tt> option is invoked.</p>
1410 <!-- _______________________________________________________________________ -->
1411 <div class="doc_subsubsection">
1412 <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
1416 <div class="doc_text">
1418 <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
1420 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
1421 except that it is designed to take values for options from an environment
1422 variable, for those cases in which reading the command line is not convenient or
1423 not desired. It fills in the values of all the command line option variables
1425 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
1428 <p>It takes three parameters: first, the name of the program (since
1429 <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
1430 second, the name of the environment variable to examine, and third, the optional
1431 <a href="#description">additional extra text</a> to emit when the
1432 <tt>--help</tt> option is invoked.</p>
1434 <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
1435 variable's value up into words and then process them using
1436 <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
1437 <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
1438 quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
1439 be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
1440 which is different from what you would get from the shell with the same
1445 <!-- _______________________________________________________________________ -->
1446 <div class="doc_subsubsection">
1447 <a name="cl::opt">The <tt>cl::opt</tt> class</a>
1450 <div class="doc_text">
1452 <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
1453 options, and is the one used most of the time. It is a templated class which
1454 can take up to three arguments (all except for the first have default values
1457 <div class="doc_code"><pre>
1458 <b>namespace</b> cl {
1459 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1460 <b>class</b> ParserClass = parser<DataType> >
1465 <p>The first template argument specifies what underlying data type the command
1466 line argument is, and is used to select a default parser implementation. The
1467 second template argument is used to specify whether the option should contain
1468 the storage for the option (the default) or whether external storage should be
1469 used to contain the value parsed for the option (see <a href="#storage">Internal
1470 vs External Storage</a> for more information).</p>
1472 <p>The third template argument specifies which parser to use. The default value
1473 selects an instantiation of the <tt>parser</tt> class based on the underlying
1474 data type of the option. In general, this default works well for most
1475 applications, so this option is only used when using a <a
1476 href="#customparser">custom parser</a>.</p>
1480 <!-- _______________________________________________________________________ -->
1481 <div class="doc_subsubsection">
1482 <a name="cl::list">The <tt>cl::list</tt> class</a>
1485 <div class="doc_text">
1487 <p>The <tt>cl::list</tt> class is the class used to represent a list of command
1488 line options. It too is a templated class which can take up to three
1491 <div class="doc_code"><pre>
1492 <b>namespace</b> cl {
1493 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1494 <b>class</b> ParserClass = parser<DataType> >
1499 <p>This class works the exact same as the <a
1500 href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
1501 the <b>type</b> of the external storage, not a boolean value. For this class,
1502 the marker type '<tt>bool</tt>' is used to indicate that internal storage should
1507 <!-- _______________________________________________________________________ -->
1508 <div class="doc_subsubsection">
1509 <a name="cl::alias">The <tt>cl::alias</tt> class</a>
1512 <div class="doc_text">
1514 <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1515 aliases for other arguments.</p>
1517 <div class="doc_code"><pre>
1518 <b>namespace</b> cl {
1523 <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
1524 used to specify which option this is an alias for. Alias arguments default to
1525 being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
1526 the conversion from string to data.</p>
1530 <!-- _______________________________________________________________________ -->
1531 <div class="doc_subsubsection">
1532 <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a>
1535 <div class="doc_text">
1537 <p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra
1538 help text to be printed out for the <tt>--help</tt> option.</p>
1540 <div class="doc_code"><pre>
1541 <b>namespace</b> cl {
1542 <b>struct</b> extrahelp;
1546 <p>To use the extrahelp, simply construct one with a <tt>const char*</tt>
1547 parameter to the constructor. The text passed to the constructor will be printed
1548 at the bottom of the help message, verbatim. Note that multiple
1549 <tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If
1550 your tool needs to print additional help information, put all that help into a
1551 single <tt>cl::extrahelp</tt> instance.</p>
1553 <div class="doc_code"><pre>
1554 cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
1558 <!-- ======================================================================= -->
1559 <div class="doc_subsection">
1560 <a name="builtinparsers">Builtin parsers</a>
1563 <div class="doc_text">
1565 <p>Parsers control how the string value taken from the command line is
1566 translated into a typed value, suitable for use in a C++ program. By default,
1567 the CommandLine library uses an instance of <tt>parser<type></tt> if the
1568 command line option specifies that it uses values of type '<tt>type</tt>'.
1569 Because of this, custom option processing is specified with specializations of
1570 the '<tt>parser</tt>' class.</p>
1572 <p>The CommandLine library provides the following builtin parser
1573 specializations, which are sufficient for most applications. It can, however,
1574 also be extended to work with new data types and new ways of interpreting the
1575 same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
1576 details on this type of library extension.</p>
1580 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
1581 can be used to map strings values to any data type, through the use of the <a
1582 href="#cl::values">cl::values</a> property, which specifies the mapping
1583 information. The most common use of this parser is for parsing enum values,
1584 which allows you to use the CommandLine library for all of the error checking to
1585 make sure that only valid enum values are specified (as opposed to accepting
1586 arbitrary strings). Despite this, however, the generic parser class can be used
1587 for any data type.</li>
1589 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
1590 is used to convert boolean strings to a boolean value. Currently accepted
1591 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1592 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
1594 <li><a name="stringparser">The <b><tt>parser<string></tt>
1595 specialization</b></a> simply stores the parsed string into the string value
1596 specified. No conversion or modification of the data is performed.</li>
1598 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
1599 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1600 accept a decimal number (with an optional '+' or '-' prefix) which must start
1601 with a non-zero digit. It accepts octal numbers, which are identified with a
1602 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1603 '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
1605 <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
1606 <b><tt>parser<float></tt> specializations</b> use the standard C
1607 <tt>strtod</tt> function to convert floating point strings into floating point
1608 values. As such, a broad range of string formats is supported, including
1609 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1616 <!-- *********************************************************************** -->
1617 <div class="doc_section">
1618 <a name="extensionguide">Extension Guide</a>
1620 <!-- *********************************************************************** -->
1622 <div class="doc_text">
1624 <p>Although the CommandLine library has a lot of functionality built into it
1625 already (as discussed previously), one of its true strengths lie in its
1626 extensibility. This section discusses how the CommandLine library works under
1627 the covers and illustrates how to do some simple, common, extensions.</p>
1631 <!-- ======================================================================= -->
1632 <div class="doc_subsection">
1633 <a name="customparser">Writing a custom parser</a>
1636 <div class="doc_text">
1638 <p>One of the simplest and most common extensions is the use of a custom parser.
1639 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1640 of the CommandLine library that turns string input from the user into a
1641 particular parsed data type, validating the input in the process.</p>
1643 <p>There are two ways to use a new parser:</p>
1649 <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1650 your custom data type.<p>
1652 <p>This approach has the advantage that users of your custom data type will
1653 automatically use your custom parser whenever they define an option with a value
1654 type of your data type. The disadvantage of this approach is that it doesn't
1655 work if your fundemental data type is something that is already supported.</p>
1661 <p>Write an independent class, using it explicitly from options that need
1664 <p>This approach works well in situations where you would line to parse an
1665 option using special syntax for a not-very-special data-type. The drawback of
1666 this approach is that users of your parser have to be aware that they are using
1667 your parser, instead of the builtin ones.</p>
1673 <p>To guide the discussion, we will discuss a custom parser that accepts file
1674 sizes, specified with an optional unit after the numeric size. For example, we
1675 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1676 this case, the underlying data type we want to parse into is
1677 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1678 this the default for all <tt>unsigned</tt> options.</p>
1680 <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
1682 <div class="doc_code"><pre>
1683 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1684 <i>// parse - Return true on error.</i>
1685 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1686 <b>unsigned</b> &Val);
1690 <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
1691 fill in the default, boiler plate, code for us. We give it the data type that
1692 we parse into (the last argument to the <tt>parse</tt> method so that clients of
1693 our custom parser know what object type to pass in to the parse method (here we
1694 declare that we parse into '<tt>unsigned</tt>' variables.</p>
1696 <p>For most purposes, the only method that must be implemented in a custom
1697 parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
1698 whenever the option is invoked, passing in the option itself, the option name,
1699 the string to parse, and a reference to a return value. If the string to parse
1700 is not well formed, the parser should output an error message and return true.
1701 Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
1702 our example, we implement <tt>parse</tt> as:</p>
1704 <div class="doc_code"><pre>
1705 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1706 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1707 <b>const char</b> *ArgStart = Arg.c_str();
1710 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1711 Val = (unsigned)strtol(ArgStart, &End, 0);
1714 <b>switch</b> (*End++) {
1715 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1716 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1717 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1720 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1721 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1722 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1725 <i>// Print an error message if unrecognized character!</i>
1726 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1732 <p>This function implements a very simple parser for the kinds of strings we are
1733 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1734 example), it is good enough for this example. Note that we use the option
1735 itself to print out the error message (the <tt>error</tt> method always returns
1736 true) in order to get a nice error message (shown below). Now that we have our
1737 parser class, we can use it like this:</p>
1739 <div class="doc_code"><pre>
1740 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1741 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1742 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1745 <p>Which adds this to the output of our program:</p>
1747 <div class="doc_code"><pre>
1749 -help - display available options (--help-hidden for more)
1751 <b>-max-file-size=<size> - Maximum file size to accept</b>
1754 <p>And we can test that our parse works correctly now (the test program just
1755 prints out the max-file-size argument value):</p>
1757 <div class="doc_code"><pre>
1760 $ ./test -max-file-size=123MB
1762 $ ./test -max-file-size=3G
1764 $ ./test -max-file-size=dog
1765 -max-file-size option: 'dog' value invalid for file size argument!
1768 <p>It looks like it works. The error message that we get is nice and helpful,
1769 and we seem to accept reasonable file sizes. This wraps up the "custom parser"
1774 <!-- ======================================================================= -->
1775 <div class="doc_subsection">
1776 <a name="explotingexternal">Exploiting external storage</a>
1779 <div class="doc_text">
1780 <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that
1781 will automatically be included in any program that links with that library.
1782 This is a feature. However, sometimes it is necessary to know the value of the
1783 command line option outside of the library. In these cases the library does or
1784 should provide an external storage location that is accessible to users of the
1785 library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the
1786 <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt>
1787 flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p>
1789 <p>TODO: complete this section</p>
1793 <!-- ======================================================================= -->
1794 <div class="doc_subsection">
1795 <a name="dynamicopts">Dynamically adding command line options</a>
1798 <div class="doc_text">
1800 <p>TODO: fill in this section</p>
1804 <!-- *********************************************************************** -->
1808 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1809 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1810 <a href="http://validator.w3.org/check/referer"><img
1811 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
1813 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1814 <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
1815 Last modified: $Date$