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12 CommandLine 2.0 Library Manual
16 <li><a href="#introduction">Introduction</a></li>
18 <li><a href="#quickstart">Quick Start Guide</a>
20 <li><a href="#bool">Boolean Arguments</a></li>
21 <li><a href="#alias">Argument Aliases</a></li>
22 <li><a href="#onealternative">Selecting an alternative from a
23 set of possibilities</a></li>
24 <li><a href="#namedalternatives">Named alternatives</a></li>
25 <li><a href="#list">Parsing a list of options</a></li>
26 <li><a href="#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
196 #include "Support/CommandLine.h"
199 <p>Additionally, you need to add this as the first line of your main
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>
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
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
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>
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>
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>
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
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>
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>
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>
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>
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>
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
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>
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
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>
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
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>
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>
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>
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>
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
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>
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>
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>
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>
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>
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>
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>
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:<pre><tt>
851 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
852 static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore);
854 int main(int argc, char**argv) {
856 std::vector<std::string>::iterator fileIt = Files.begin();
857 std::vector<std::string>::iterator libIt = Libraries.begin();
858 unsigned libPos = 0, filePos = 0;
860 if ( libIt != Libraries.end() )
861 libPos = Libraries.getPosition( libIt - Libraries.begin() );
864 if ( fileIt != Files.end() )
865 filePos = Files.getPosition( fileIt - Files.begin() );
869 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
870 // Source File Is next
873 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
878 break; // we're done with the list
882 <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an
883 <tt>unsigned getPosition()</tt> option that will provide the absolute position
884 of that option. You can apply the same approach as above with a
885 <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p>
888 <!-- _______________________________________________________________________ -->
889 <div class="doc_subsubsection">
890 <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
893 <div class="doc_text">
895 <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
896 used to construct programs that use "interpreter style" option processing. With
897 this style of option processing, all arguments specified after the last
898 positional argument are treated as special interpreter arguments that are not
899 interpreted by the command line argument.</p>
901 <p>As a concrete example, lets say we are developing a replacement for the
902 standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
903 you specify options to the shell itself (like <tt>-x</tt> which turns on trace
904 output), then you specify the name of the script to run, then you specify
905 arguments to the script. These arguments to the script are parsed by the bourne
906 shell command line option processor, but are not interpreted as options to the
907 shell itself. Using the CommandLine library, we would specify this as:</p>
910 <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>("-"));
911 <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>"));
912 <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
915 <p>which automatically provides the help output:</p>
918 USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
921 -help - display available options (--help-hidden for more)
922 <b>-x - Enable trace output</b>
925 <p>At runtime, if we run our new shell replacement as '<tt>spiffysh -x test.sh
926 -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
927 <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
928 <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
929 were specified after the last positional argument (which is the script
932 <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
933 be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
934 per program, there must be at least one <a href="#positional">positional
935 argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
936 positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
937 href="#cl::list">cl::list</a> option.</p>
941 <!-- ======================================================================= -->
942 <div class="doc_subsection">
943 <a name="storage">Internal vs External Storage</a>
946 <div class="doc_text">
948 <p>By default, all command line options automatically hold the value that they
949 parse from the command line. This is very convenient in the common case,
950 especially when combined with the ability to define command line options in the
951 files that use them. This is called the internal storage model.</p>
953 <p>Sometimes, however, it is nice to separate the command line option processing
954 code from the storage of the value parsed. For example, lets say that we have a
955 '<tt>-debug</tt>' option that we would like to use to enable debug information
956 across the entire body of our program. In this case, the boolean value
957 controlling the debug code should be globally accessable (in a header file, for
958 example) yet the command line option processing code should not be exposed to
959 all of these clients (requiring lots of .cpp files to #include
960 <tt>CommandLine.h</tt>).</p>
962 <p>To do this, set up your .h file with your option, like this for example:</p>
965 <i>// DebugFlag.h - Get access to the '-debug' command line option
968 // DebugFlag - This boolean is set to true if the '-debug' command line option
969 // is specified. This should probably not be referenced directly, instead, use
970 // the DEBUG macro below.
972 extern bool DebugFlag;
974 <i>// DEBUG macro - This macro should be used by code to emit debug information.
975 // In the '-debug' option is specified on the command line, and if this is a
976 // debug build, then the code specified as the option to the macro will be
977 // executed. Otherwise it will not be. Example:
979 // DEBUG(cerr << "Bitset contains: " << Bitset << "\n");
981 <span class="doc_red">#ifdef NDEBUG
984 #define DEBUG(X)</span> \
985 do { if (DebugFlag) { X; } } while (0)
986 <span class="doc_red">#endif</span>
989 <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
990 <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
991 set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
992 an additial argument to our command line argument processor, and we specify
993 where to fill in with the <a href="#cl::location">cl::location</a>
997 bool DebugFlag; <i>// the actual value</i>
998 static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
999 Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>,
1000 <a href="#cl::location">cl::location</a>(DebugFlag));
1003 <p>In the above example, we specify "<tt>true</tt>" as the second argument to
1004 the <a href="#cl::opt">cl::opt</a> template, indicating that the template should
1005 not maintain a copy of the value itself. In addition to this, we specify the <a
1006 href="#cl::location">cl::location</a> attribute, so that <tt>DebugFlag</tt> is
1007 automatically set.</p>
1011 <!-- ======================================================================= -->
1012 <div class="doc_subsection">
1013 <a name="attributes">Option Attributes</a>
1016 <div class="doc_text">
1018 <p>This section describes the basic attributes that you can specify on
1023 <li>The option name attribute (which is required for all options, except <a
1024 href="#positional">positional options</a>) specifies what the option name is.
1025 This option is specified in simple double quotes:
1028 <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
1033 <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
1034 description for the option to be shown in the <tt>--help</tt> output for the
1037 <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
1038 specifies a string that can be used to fine tune the <tt>--help</tt> output for
1039 a command line option. Look <a href="#value_desc_example">here</a> for an
1042 <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
1043 inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
1044 not specified then the command line option value defaults to the value created
1045 by the default constructor for the type. <b>Warning</b>: If you specify both
1046 <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
1047 you must specify <b><tt>cl::location</tt></b> first, so that when the
1048 command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
1049 initial value. (You will get an error at runtime if you don't put them in
1050 the right order.)</li>
1052 <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
1053 store the value for a parsed command line option if using external storage. See
1054 the section on <a href="#storage">Internal vs External Storage</a> for more
1057 <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
1058 specifies which option a <a href="#cl::alias">cl::alias</a> option is an alias
1061 <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
1062 the string-to-value mapping to be used by the generic parser. It takes a
1063 <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
1065 specify the option name, the value mapped to, and the description shown in the
1066 <tt>--help</tt> for the tool. Because the generic parser is used most
1067 frequently with enum values, two macros are often useful:
1071 <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
1072 nice simple way to specify a triplet for an enum. This macro automatically
1073 makes the option name be the same as the enum name. The first option to the
1074 macro is the enum, the second is the description for the command line
1077 <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
1078 specify macro options where the option name doesn't equal the enum name. For
1079 this macro, the first argument is the enum value, the second is the flag name,
1080 and the second is the description.</li>
1084 You will get a compile time error if you try to use cl::values with a parser
1085 that does not support it.</li>
1091 <!-- ======================================================================= -->
1092 <div class="doc_subsection">
1093 <a name="modifiers">Option Modifiers</a>
1096 <div class="doc_text">
1098 <p>Option modifiers are the flags and expressions that you pass into the
1099 constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1100 href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
1101 tweak how options are parsed and how <tt>--help</tt> output is generated to fit
1102 your application well.</p>
1104 <p>These options fall into five main catagories:</p>
1107 <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
1108 <li><a href="#numoccurrences">Controlling the number of occurrences
1109 required and allowed</a></li>
1110 <li><a href="#valrequired">Controlling whether or not a value must be
1112 <li><a href="#formatting">Controlling other formatting options</a></li>
1113 <li><a href="#misc">Miscellaneous option modifiers</a></li>
1116 <p>It is not possible to specify two options from the same catagory (you'll get
1117 a runtime error) to a single option, except for options in the miscellaneous
1118 catagory. The CommandLine library specifies defaults for all of these settings
1119 that are the most useful in practice and the most common, which mean that you
1120 usually shouldn't have to worry about these.</p>
1124 <!-- _______________________________________________________________________ -->
1125 <div class="doc_subsubsection">
1126 <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
1129 <div class="doc_text">
1131 <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
1132 <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
1133 appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
1134 compiled program:</p>
1138 <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
1139 (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1140 href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
1141 in both help listings.</li>
1143 <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
1144 default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
1145 the option should not appear in the <tt>--help</tt> output, but should appear in
1146 the <tt>--help-hidden</tt> output.</li>
1148 <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
1149 indicates that the option should not appear in any help output.</li>
1155 <!-- _______________________________________________________________________ -->
1156 <div class="doc_subsubsection">
1157 <a name="numoccurrences">Controlling the number of occurrences required and
1161 <div class="doc_text">
1163 <p>This group of options is used to control how many time an option is allowed
1164 (or required) to be specified on the command line of your program. Specifying a
1165 value for this setting allows the CommandLine library to do error checking for
1168 <p>The allowed values for this option group are:</p>
1172 <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
1173 is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
1174 href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
1175 allow either zero or one occurrence of the option to be specified.</li>
1177 <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
1178 (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
1179 indicates that your program will allow the option to be specified zero or more
1182 <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
1183 indicates that the specified option must be specified exactly one time.</li>
1185 <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
1186 indicates that the option must be specified at least one time.</li>
1188 <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
1189 href="#positional">Positional arguments section</a></li>
1193 <p>If an option is not specified, then the value of the option is equal to the
1194 value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
1195 the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
1196 option value is initialized with the default constructor for the data type.</p>
1198 <p>If an option is specified multiple times for an option of the <tt><a
1199 href="#cl::opt">cl::opt</a></tt> class, only the last value will be
1204 <!-- _______________________________________________________________________ -->
1205 <div class="doc_subsubsection">
1206 <a name="valrequired">Controlling whether or not a value must be specified</a>
1209 <div class="doc_text">
1211 <p>This group of options is used to control whether or not the option allows a
1212 value to be present. In the case of the CommandLine library, a value is either
1213 specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
1214 string (e.g. '<tt>-o a.out</tt>').</p>
1216 <p>The allowed values for this option group are:</p>
1220 <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
1221 (which is the default for <tt>bool</tt> typed options) specifies that it is
1222 acceptable to have a value, or not. A boolean argument can be enabled just by
1223 appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
1224 If an option is specified with this mode, it is illegal for the value to be
1225 provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
1226 get this behavior, you must use the <a
1227 href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
1229 <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
1230 (which is the default for all other types except for <a
1231 href="#onealternative">unnamed alternatives using the generic parser</a>)
1232 specifies that a value must be provided. This mode informs the command line
1233 library that if an option is not provides with an equal sign, that the next
1234 argument provided must be the value. This allows things like '<tt>-o
1235 a.out</tt>' to work.</li>
1237 <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
1238 modifier (which is the default for <a href="#onealternative">unnamed
1239 alternatives using the generic parser</a>) indicates that it is a runtime error
1240 for the user to specify a value. This can be provided to disallow users from
1241 providing options to boolean options (like '<tt>-foo=true</tt>').</li>
1245 <p>In general, the default values for this option group work just like you would
1246 want them to. As mentioned above, you can specify the <a
1247 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
1248 argument to restrict your command line parser. These options are mostly useful
1249 when <a href="#extensionguide">extending the library</a>.</p>
1253 <!-- _______________________________________________________________________ -->
1254 <div class="doc_subsubsection">
1255 <a name="formatting">Controlling other formatting options</a>
1258 <div class="doc_text">
1260 <p>The formatting option group is used to specify that the command line option
1261 has special abilities and is otherwise different from other command line
1262 arguments. As usual, you can only specify at most one of these arguments.</p>
1266 <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
1267 modifier (which is the default all options) specifies that this option is
1270 <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
1271 specifies that this is a positional argument, that does not have a command line
1272 option associated with it. See the <a href="#positional">Positional
1273 Arguments</a> section for more information.</li>
1275 <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
1276 specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
1278 <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
1279 that this option prefixes its value. With 'Prefix' options, the equal sign does
1280 not separate the value from the option name specified. Instead, the value is
1281 everything after the prefix, including any equal sign if present. This is useful
1282 for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a
1283 linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the
1284 '<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list)
1285 options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
1286 allow the CommandLine library to recognize them. Note that
1287 <a href="#cl::Prefix">cl::Prefix</a> options must not have the <a
1288 href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li>
1290 <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
1291 to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
1292 arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
1293 command actually enables four different options, all of which are single
1294 letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
1299 <p>The CommandLine library does not restrict how you use the <a
1300 href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
1301 modifiers, but it is possible to specify ambiguous argument settings. Thus, it
1302 is possible to have multiple letter options that are prefix or grouping options,
1303 and they will still work as designed.</p>
1305 <p>To do this, the CommandLine library uses a greedy algorithm to parse the
1306 input option into (potentially multiple) prefix and grouping options. The
1307 strategy basically looks like this:</p>
1309 <p><tt>parse(string OrigInput) {</tt>
1312 <li><tt>string input = OrigInput;</tt>
1313 <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
1314 <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
1315 <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
1316 <li><tt>if (getOption(input).isPrefix())<br>
1317 return getOption(input).parse(input);</tt>
1318 <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
1319 getOption(input).parse();<br>
1320 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
1321 input = OrigInput;<br>
1322 while (!isOption(input) && !input.empty()) input.pop_back();<br>
1324 <li><tt>if (!OrigInput.empty()) error();</tt></li>
1332 <!-- _______________________________________________________________________ -->
1333 <div class="doc_subsubsection">
1334 <a name="misc">Miscellaneous option modifiers</a>
1337 <div class="doc_text">
1339 <p>The miscellaneous option modifiers are the only flags where you can specify
1340 more than one flag from the set: they are not mutually exclusive. These flags
1341 specify boolean properties that modify the option.</p>
1345 <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
1346 indicates that any commas specified for an option's value should be used to
1347 split the value up into multiple values for the option. For example, these two
1348 options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
1349 "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
1350 makes sense to be used in a case where the option is allowed to accept one or
1351 more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
1353 <li><a name="cl::PositionalEatsArgs">The
1354 <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
1355 positional arguments, and only makes sense for lists) indicates that positional
1356 argument should consume any strings after it (including strings that start with
1357 a "-") up until another recognized positional argument. For example, if you
1358 have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the
1359 string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
1360 -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
1361 "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
1365 <p>So far, these are the only two miscellaneous option modifiers.</p>
1369 <!-- ======================================================================= -->
1370 <div class="doc_subsection">
1371 <a name="toplevel">Top-Level Classes and Functions</a>
1374 <div class="doc_text">
1376 <p>Despite all of the built-in flexibility, the CommandLine option library
1377 really only consists of one function (<a
1378 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
1379 and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
1380 href="#cl::list"><tt>cl::list</tt></a>, and <a
1381 href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
1382 classes in detail.</p>
1386 <!-- _______________________________________________________________________ -->
1387 <div class="doc_subsubsection">
1388 <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
1392 <div class="doc_text">
1394 <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
1395 directly from <tt>main</tt>, and is used to fill in the values of all of the
1396 command line option variables once <tt>argc</tt> and <tt>argv</tt> are
1399 <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
1400 (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
1401 which holds <a href="#description">additional extra text</a> to emit when the
1402 <tt>--help</tt> option is invoked.</p>
1406 <!-- _______________________________________________________________________ -->
1407 <div class="doc_subsubsection">
1408 <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
1412 <div class="doc_text">
1414 <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
1416 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
1417 except that it is designed to take values for options from an environment
1418 variable, for those cases in which reading the command line is not convenient or
1419 not desired. It fills in the values of all the command line option variables
1421 href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
1424 <p>It takes three parameters: first, the name of the program (since
1425 <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
1426 second, the name of the environment variable to examine, and third, the optional
1427 <a href="#description">additional extra text</a> to emit when the
1428 <tt>--help</tt> option is invoked.</p>
1430 <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
1431 variable's value up into words and then process them using
1432 <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
1433 <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
1434 quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
1435 be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
1436 which is different from what you would get from the shell with the same
1441 <!-- _______________________________________________________________________ -->
1442 <div class="doc_subsubsection">
1443 <a name="cl::opt">The <tt>cl::opt</tt> class</a>
1446 <div class="doc_text">
1448 <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
1449 options, and is the one used most of the time. It is a templated class which
1450 can take up to three arguments (all except for the first have default values
1454 <b>namespace</b> cl {
1455 <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
1456 <b>class</b> ParserClass = parser<DataType> >
1461 <p>The first template argument specifies what underlying data type the command
1462 line argument is, and is used to select a default parser implementation. The
1463 second template argument is used to specify whether the option should contain
1464 the storage for the option (the default) or whether external storage should be
1465 used to contain the value parsed for the option (see <a href="#storage">Internal
1466 vs External Storage</a> for more information).</p>
1468 <p>The third template argument specifies which parser to use. The default value
1469 selects an instantiation of the <tt>parser</tt> class based on the underlying
1470 data type of the option. In general, this default works well for most
1471 applications, so this option is only used when using a <a
1472 href="#customparser">custom parser</a>.</p>
1476 <!-- _______________________________________________________________________ -->
1477 <div class="doc_subsubsection">
1478 <a name="cl::list">The <tt>cl::list</tt> class</a>
1481 <div class="doc_text">
1483 <p>The <tt>cl::list</tt> class is the class used to represent a list of command
1484 line options. It too is a templated class which can take up to three
1488 <b>namespace</b> cl {
1489 <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
1490 <b>class</b> ParserClass = parser<DataType> >
1495 <p>This class works the exact same as the <a
1496 href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
1497 the <b>type</b> of the external storage, not a boolean value. For this class,
1498 the marker type '<tt>bool</tt>' is used to indicate that internal storage should
1503 <!-- _______________________________________________________________________ -->
1504 <div class="doc_subsubsection">
1505 <a name="cl::alias">The <tt>cl::alias</tt> class</a>
1508 <div class="doc_text">
1510 <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
1511 aliases for other arguments.</p>
1514 <b>namespace</b> cl {
1519 <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
1520 used to specify which option this is an alias for. Alias arguments default to
1521 being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
1522 the conversion from string to data.</p>
1526 <!-- _______________________________________________________________________ -->
1527 <div class="doc_subsubsection">
1528 <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a>
1531 <div class="doc_text">
1533 <p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra
1534 help text to be printed out for the <tt>--help</tt> option.</p>
1537 <b>namespace</b> cl {
1538 <b>struct</b> extrahelp;
1542 <p>To use the extrahelp, simply construct one with a <tt>const char*</tt>
1543 parameter to the constructor. The text passed to the constructor will be printed
1544 at the bottom of the help message, verbatim. Note that multiple
1545 <tt>cl::extrahelp</tt> <b>can</b> be used but this practice is discouraged. If
1546 your tool needs to print additional help information, put all that help into a
1547 single <tt>cl::extrahelp</tt> instance.</p>
1550 cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
1554 <!-- ======================================================================= -->
1555 <div class="doc_subsection">
1556 <a name="builtinparsers">Builtin parsers</a>
1559 <div class="doc_text">
1561 <p>Parsers control how the string value taken from the command line is
1562 translated into a typed value, suitable for use in a C++ program. By default,
1563 the CommandLine library uses an instance of <tt>parser<type></tt> if the
1564 command line option specifies that it uses values of type '<tt>type</tt>'.
1565 Because of this, custom option processing is specified with specializations of
1566 the '<tt>parser</tt>' class.</p>
1568 <p>The CommandLine library provides the following builtin parser
1569 specializations, which are sufficient for most applications. It can, however,
1570 also be extended to work with new data types and new ways of interpreting the
1571 same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
1572 details on this type of library extension.</p>
1576 <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
1577 can be used to map strings values to any data type, through the use of the <a
1578 href="#cl::values">cl::values</a> property, which specifies the mapping
1579 information. The most common use of this parser is for parsing enum values,
1580 which allows you to use the CommandLine library for all of the error checking to
1581 make sure that only valid enum values are specified (as opposed to accepting
1582 arbitrary strings). Despite this, however, the generic parser class can be used
1583 for any data type.</li>
1585 <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
1586 is used to convert boolean strings to a boolean value. Currently accepted
1587 strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
1588 "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
1590 <li><a name="stringparser">The <b><tt>parser<string></tt>
1591 specialization</b></a> simply stores the parsed string into the string value
1592 specified. No conversion or modification of the data is performed.</li>
1594 <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
1595 uses the C <tt>strtol</tt> function to parse the string input. As such, it will
1596 accept a decimal number (with an optional '+' or '-' prefix) which must start
1597 with a non-zero digit. It accepts octal numbers, which are identified with a
1598 '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
1599 '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
1601 <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
1602 <b><tt>parser<float></tt> specializations</b> use the standard C
1603 <tt>strtod</tt> function to convert floating point strings into floating point
1604 values. As such, a broad range of string formats is supported, including
1605 exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
1612 <!-- *********************************************************************** -->
1613 <div class="doc_section">
1614 <a name="extensionguide">Extension Guide</a>
1616 <!-- *********************************************************************** -->
1618 <div class="doc_text">
1620 <p>Although the CommandLine library has a lot of functionality built into it
1621 already (as discussed previously), one of its true strengths lie in its
1622 extensibility. This section discusses how the CommandLine library works under
1623 the covers and illustrates how to do some simple, common, extensions.</p>
1627 <!-- ======================================================================= -->
1628 <div class="doc_subsection">
1629 <a name="customparser">Writing a custom parser</a>
1632 <div class="doc_text">
1634 <p>One of the simplest and most common extensions is the use of a custom parser.
1635 As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
1636 of the CommandLine library that turns string input from the user into a
1637 particular parsed data type, validating the input in the process.</p>
1639 <p>There are two ways to use a new parser:</p>
1645 <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
1646 your custom data type.<p>
1648 <p>This approach has the advantage that users of your custom data type will
1649 automatically use your custom parser whenever they define an option with a value
1650 type of your data type. The disadvantage of this approach is that it doesn't
1651 work if your fundemental data type is something that is already supported.</p>
1657 <p>Write an independent class, using it explicitly from options that need
1660 <p>This approach works well in situations where you would line to parse an
1661 option using special syntax for a not-very-special data-type. The drawback of
1662 this approach is that users of your parser have to be aware that they are using
1663 your parser, instead of the builtin ones.</p>
1669 <p>To guide the discussion, we will discuss a custom parser that accepts file
1670 sizes, specified with an optional unit after the numeric size. For example, we
1671 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1672 this case, the underlying data type we want to parse into is
1673 '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
1674 this the default for all <tt>unsigned</tt> options.</p>
1676 <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
1679 <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
1680 <i>// parse - Return true on error.</i>
1681 <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
1682 <b>unsigned</b> &Val);
1686 <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
1687 fill in the default, boiler plate, code for us. We give it the data type that
1688 we parse into (the last argument to the <tt>parse</tt> method so that clients of
1689 our custom parser know what object type to pass in to the parse method (here we
1690 declare that we parse into '<tt>unsigned</tt>' variables.</p>
1692 <p>For most purposes, the only method that must be implemented in a custom
1693 parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
1694 whenever the option is invoked, passing in the option itself, the option name,
1695 the string to parse, and a reference to a return value. If the string to parse
1696 is not well formed, the parser should output an error message and return true.
1697 Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
1698 our example, we implement <tt>parse</tt> as:</p>
1701 <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
1702 <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
1703 <b>const char</b> *ArgStart = Arg.c_str();
1706 <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
1707 Val = (unsigned)strtol(ArgStart, &End, 0);
1710 <b>switch</b> (*End++) {
1711 <b>case</b> 0: <b>return</b> false; <i>// No error</i>
1712 <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
1713 <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
1716 <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
1717 <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
1718 <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
1721 <i>// Print an error message if unrecognized character!</i>
1722 <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
1728 <p>This function implements a very simple parser for the kinds of strings we are
1729 interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
1730 example), it is good enough for this example. Note that we use the option
1731 itself to print out the error message (the <tt>error</tt> method always returns
1732 true) in order to get a nice error message (shown below). Now that we have our
1733 parser class, we can use it like this:</p>
1736 <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
1737 MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
1738 <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
1741 <p>Which adds this to the output of our program:</p>
1745 -help - display available options (--help-hidden for more)
1747 <b>-max-file-size=<size> - Maximum file size to accept</b>
1750 <p>And we can test that our parse works correctly now (the test program just
1751 prints out the max-file-size argument value):</p>
1756 $ ./test -max-file-size=123MB
1758 $ ./test -max-file-size=3G
1760 $ ./test -max-file-size=dog
1761 -max-file-size option: 'dog' value invalid for file size argument!
1764 <p>It looks like it works. The error message that we get is nice and helpful,
1765 and we seem to accept reasonable file sizes. This wraps up the "custom parser"
1770 <!-- ======================================================================= -->
1771 <div class="doc_subsection">
1772 <a name="explotingexternal">Exploiting external storage</a>
1775 <div class="doc_text">
1776 <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that
1777 will automatically be included in any program that links with that library.
1778 This is a feature. However, sometimes it is necessary to know the value of the
1779 command line option outside of the library. In these cases the library does or
1780 should provide an external storage location that is accessible to users of the
1781 library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the
1782 <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt>
1783 flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p>
1785 <p>TODO: complete this section</p>
1789 <!-- ======================================================================= -->
1790 <div class="doc_subsection">
1791 <a name="dynamicopts">Dynamically adding command line options</a>
1794 <div class="doc_text">
1796 <p>TODO: fill in this section</p>
1800 <!-- *********************************************************************** -->
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