1 ==============================
2 CommandLine 2.0 Library Manual
3 ==============================
11 This document describes the CommandLine argument processing library. It will
12 show you how to use it, and what it can do. The CommandLine library uses a
13 declarative approach to specifying the command line options that your program
14 takes. By default, these options declarations implicitly hold the value parsed
15 for the option declared (of course this `can be changed`_).
17 Although there are a **lot** of command line argument parsing libraries out
18 there in many different languages, none of them fit well with what I needed. By
19 looking at the features and problems of other libraries, I designed the
20 CommandLine library to have the following features:
22 #. Speed: The CommandLine library is very quick and uses little resources. The
23 parsing time of the library is directly proportional to the number of
24 arguments parsed, not the number of options recognized. Additionally,
25 command line argument values are captured transparently into user defined
26 global variables, which can be accessed like any other variable (and with the
29 #. Type Safe: As a user of CommandLine, you don't have to worry about
30 remembering the type of arguments that you want (is it an int? a string? a
31 bool? an enum?) and keep casting it around. Not only does this help prevent
32 error prone constructs, it also leads to dramatically cleaner source code.
34 #. No subclasses required: To use CommandLine, you instantiate variables that
35 correspond to the arguments that you would like to capture, you don't
36 subclass a parser. This means that you don't have to write **any**
39 #. Globally accessible: Libraries can specify command line arguments that are
40 automatically enabled in any tool that links to the library. This is
41 possible because the application doesn't have to keep a list of arguments to
42 pass to the parser. This also makes supporting `dynamically loaded options`_
45 #. Cleaner: CommandLine supports enum and other types directly, meaning that
46 there is less error and more security built into the library. You don't have
47 to worry about whether your integral command line argument accidentally got
48 assigned a value that is not valid for your enum type.
50 #. Powerful: The CommandLine library supports many different types of arguments,
51 from simple `boolean flags`_ to `scalars arguments`_ (`strings`_,
52 `integers`_, `enums`_, `doubles`_), to `lists of arguments`_. This is
53 possible because CommandLine is...
55 #. Extensible: It is very simple to add a new argument type to CommandLine.
56 Simply specify the parser that you want to use with the command line option
57 when you declare it. `Custom parsers`_ are no problem.
59 #. Labor Saving: The CommandLine library cuts down on the amount of grunt work
60 that you, the user, have to do. For example, it automatically provides a
61 ``-help`` option that shows the available command line options for your tool.
62 Additionally, it does most of the basic correctness checking for you.
64 #. Capable: The CommandLine library can handle lots of different forms of
65 options often found in real programs. For example, `positional`_ arguments,
66 ``ls`` style `grouping`_ options (to allow processing '``ls -lad``'
67 naturally), ``ld`` style `prefix`_ options (to parse '``-lmalloc
68 -L/usr/lib``'), and interpreter style options.
70 This document will hopefully let you jump in and start using CommandLine in your
71 utility quickly and painlessly. Additionally it should be a simple reference
72 manual to figure out how stuff works.
77 This section of the manual runs through a simple CommandLine'ification of a
78 basic compiler tool. This is intended to show you how to jump into using the
79 CommandLine library in your own program, and show you some of the cool things it
82 To start out, you need to include the CommandLine header file into your program:
86 #include "llvm/Support/CommandLine.h"
88 Additionally, you need to add this as the first line of your main program:
92 int main(int argc, char **argv) {
93 cl::ParseCommandLineOptions(argc, argv);
97 ... which actually parses the arguments and fills in the variable declarations.
99 Now that you are ready to support command line arguments, we need to tell the
100 system which ones we want, and what type of arguments they are. The CommandLine
101 library uses a declarative syntax to model command line arguments with the
102 global variable declarations that capture the parsed values. This means that
103 for every command line option that you would like to support, there should be a
104 global variable declaration to capture the result. For example, in a compiler,
105 we would like to support the Unix-standard '``-o <filename>``' option to specify
106 where to put the output. With the CommandLine library, this is represented like
109 .. _scalars arguments:
114 cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename"));
116 This declares a global variable "``OutputFilename``" that is used to capture the
117 result of the "``o``" argument (first parameter). We specify that this is a
118 simple scalar option by using the "``cl::opt``" template (as opposed to the
119 "``cl::list``" template), and tell the CommandLine library that the data
120 type that we are parsing is a string.
122 The second and third parameters (which are optional) are used to specify what to
123 output for the "``-help``" option. In this case, we get a line that looks like
128 USAGE: compiler [options]
131 -help - display available options (-help-hidden for more)
132 -o <filename> - Specify output filename
134 Because we specified that the command line option should parse using the
135 ``string`` data type, the variable declared is automatically usable as a real
136 string in all contexts that a normal C++ string object may be used. For
142 std::ofstream Output(OutputFilename.c_str());
143 if (Output.good()) ...
146 There are many different options that you can use to customize the command line
147 option handling library, but the above example shows the general interface to
148 these options. The options can be specified in any order, and are specified
149 with helper functions like `cl::desc(...)`_, so there are no positional
150 dependencies to remember. The available options are discussed in detail in the
153 Continuing the example, we would like to have our compiler take an input
154 filename as well as an output filename, but we do not want the input filename to
155 be specified with a hyphen (ie, not ``-filename.c``). To support this style of
156 argument, the CommandLine library allows for `positional`_ arguments to be
157 specified for the program. These positional arguments are filled with command
158 line parameters that are not in option form. We use this feature like this:
163 cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-"));
165 This declaration indicates that the first positional argument should be treated
166 as the input filename. Here we use the `cl::init`_ option to specify an initial
167 value for the command line option, which is used if the option is not specified
168 (if you do not specify a `cl::init`_ modifier for an option, then the default
169 constructor for the data type is used to initialize the value). Command line
170 options default to being optional, so if we would like to require that the user
171 always specify an input filename, we would add the `cl::Required`_ flag, and we
172 could eliminate the `cl::init`_ modifier, like this:
176 cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::Required);
178 Again, the CommandLine library does not require the options to be specified in
179 any particular order, so the above declaration is equivalent to:
183 cl::opt<string> InputFilename(cl::Positional, cl::Required, cl::desc("<input file>"));
185 By simply adding the `cl::Required`_ flag, the CommandLine library will
186 automatically issue an error if the argument is not specified, which shifts all
187 of the command line option verification code out of your application into the
188 library. This is just one example of how using flags can alter the default
189 behaviour of the library, on a per-option basis. By adding one of the
190 declarations above, the ``-help`` option synopsis is now extended to:
194 USAGE: compiler [options] <input file>
197 -help - display available options (-help-hidden for more)
198 -o <filename> - Specify output filename
200 ... indicating that an input filename is expected.
205 In addition to input and output filenames, we would like the compiler example to
206 support three boolean flags: "``-f``" to force writing binary output to a
207 terminal, "``--quiet``" to enable quiet mode, and "``-q``" for backwards
208 compatibility with some of our users. We can support these by declaring options
209 of boolean type like this:
213 cl::opt<bool> Force ("f", cl::desc("Enable binary output on terminals"));
214 cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages"));
215 cl::opt<bool> Quiet2("q", cl::desc("Don't print informational messages"), cl::Hidden);
217 This does what you would expect: it declares three boolean variables
218 ("``Force``", "``Quiet``", and "``Quiet2``") to recognize these options. Note
219 that the "``-q``" option is specified with the "`cl::Hidden`_" flag. This
220 modifier prevents it from being shown by the standard "``-help``" output (note
221 that it is still shown in the "``-help-hidden``" output).
223 The CommandLine library uses a `different parser`_ for different data types.
224 For example, in the string case, the argument passed to the option is copied
225 literally into the content of the string variable... we obviously cannot do that
226 in the boolean case, however, so we must use a smarter parser. In the case of
227 the boolean parser, it allows no options (in which case it assigns the value of
228 true to the variable), or it allows the values "``true``" or "``false``" to be
229 specified, allowing any of the following inputs:
233 compiler -f # No value, 'Force' == true
234 compiler -f=true # Value specified, 'Force' == true
235 compiler -f=TRUE # Value specified, 'Force' == true
236 compiler -f=FALSE # Value specified, 'Force' == false
238 ... you get the idea. The `bool parser`_ just turns the string values into
239 boolean values, and rejects things like '``compiler -f=foo``'. Similarly, the
240 `float`_, `double`_, and `int`_ parsers work like you would expect, using the
241 '``strtol``' and '``strtod``' C library calls to parse the string value into the
244 With the declarations above, "``compiler -help``" emits this:
248 USAGE: compiler [options] <input file>
251 -f - Enable binary output on terminals
252 -o - Override output filename
253 -quiet - Don't print informational messages
254 -help - display available options (-help-hidden for more)
256 and "``compiler -help-hidden``" prints this:
260 USAGE: compiler [options] <input file>
263 -f - Enable binary output on terminals
264 -o - Override output filename
265 -q - Don't print informational messages
266 -quiet - Don't print informational messages
267 -help - display available options (-help-hidden for more)
269 This brief example has shown you how to use the '`cl::opt`_' class to parse
270 simple scalar command line arguments. In addition to simple scalar arguments,
271 the CommandLine library also provides primitives to support CommandLine option
272 `aliases`_, and `lists`_ of options.
279 So far, the example works well, except for the fact that we need to check the
280 quiet condition like this now:
285 if (!Quiet && !Quiet2) printInformationalMessage(...);
288 ... which is a real pain! Instead of defining two values for the same
289 condition, we can use the "`cl::alias`_" class to make the "``-q``" option an
290 **alias** for the "``-quiet``" option, instead of providing a value itself:
294 cl::opt<bool> Force ("f", cl::desc("Overwrite output files"));
295 cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages"));
296 cl::alias QuietA("q", cl::desc("Alias for -quiet"), cl::aliasopt(Quiet));
298 The third line (which is the only one we modified from above) defines a "``-q``"
299 alias that updates the "``Quiet``" variable (as specified by the `cl::aliasopt`_
300 modifier) whenever it is specified. Because aliases do not hold state, the only
301 thing the program has to query is the ``Quiet`` variable now. Another nice
302 feature of aliases is that they automatically hide themselves from the ``-help``
303 output (although, again, they are still visible in the ``-help-hidden output``).
305 Now the application code can simply use:
310 if (!Quiet) printInformationalMessage(...);
313 ... which is much nicer! The "`cl::alias`_" can be used to specify an
314 alternative name for any variable type, and has many uses.
316 .. _unnamed alternatives using the generic parser:
318 Selecting an alternative from a set of possibilities
319 ----------------------------------------------------
321 So far we have seen how the CommandLine library handles builtin types like
322 ``std::string``, ``bool`` and ``int``, but how does it handle things it doesn't
323 know about, like enums or '``int*``'s?
325 The answer is that it uses a table-driven generic parser (unless you specify
326 your own parser, as described in the `Extension Guide`_). This parser maps
327 literal strings to whatever type is required, and requires you to tell it what
328 this mapping should be.
330 Let's say that we would like to add four optimization levels to our optimizer,
331 using the standard flags "``-g``", "``-O0``", "``-O1``", and "``-O2``". We
332 could easily implement this with boolean options like above, but there are
333 several problems with this strategy:
335 #. A user could specify more than one of the options at a time, for example,
336 "``compiler -O3 -O2``". The CommandLine library would not be able to catch
337 this erroneous input for us.
339 #. We would have to test 4 different variables to see which ones are set.
341 #. This doesn't map to the numeric levels that we want... so we cannot easily
342 see if some level >= "``-O1``" is enabled.
344 To cope with these problems, we can use an enum value, and have the CommandLine
345 library fill it in with the appropriate level directly, which is used like this:
353 cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"),
355 clEnumVal(g , "No optimizations, enable debugging"),
356 clEnumVal(O1, "Enable trivial optimizations"),
357 clEnumVal(O2, "Enable default optimizations"),
358 clEnumVal(O3, "Enable expensive optimizations"),
362 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
365 This declaration defines a variable "``OptimizationLevel``" of the
366 "``OptLevel``" enum type. This variable can be assigned any of the values that
367 are listed in the declaration (Note that the declaration list must be terminated
368 with the "``clEnumValEnd``" argument!). The CommandLine library enforces that
369 the user can only specify one of the options, and it ensure that only valid enum
370 values can be specified. The "``clEnumVal``" macros ensure that the command
371 line arguments matched the enum values. With this option added, our help output
376 USAGE: compiler [options] <input file>
379 Choose optimization level:
380 -g - No optimizations, enable debugging
381 -O1 - Enable trivial optimizations
382 -O2 - Enable default optimizations
383 -O3 - Enable expensive optimizations
384 -f - Enable binary output on terminals
385 -help - display available options (-help-hidden for more)
386 -o <filename> - Specify output filename
387 -quiet - Don't print informational messages
389 In this case, it is sort of awkward that flag names correspond directly to enum
390 names, because we probably don't want a enum definition named "``g``" in our
391 program. Because of this, we can alternatively write this example like this:
399 cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"),
401 clEnumValN(Debug, "g", "No optimizations, enable debugging"),
402 clEnumVal(O1 , "Enable trivial optimizations"),
403 clEnumVal(O2 , "Enable default optimizations"),
404 clEnumVal(O3 , "Enable expensive optimizations"),
408 if (OptimizationLevel == Debug) outputDebugInfo(...);
411 By using the "``clEnumValN``" macro instead of "``clEnumVal``", we can directly
412 specify the name that the flag should get. In general a direct mapping is nice,
413 but sometimes you can't or don't want to preserve the mapping, which is when you
419 Another useful argument form is a named alternative style. We shall use this
420 style in our compiler to specify different debug levels that can be used.
421 Instead of each debug level being its own switch, we want to support the
422 following options, of which only one can be specified at a time:
423 "``--debug-level=none``", "``--debug-level=quick``",
424 "``--debug-level=detailed``". To do this, we use the exact same format as our
425 optimization level flags, but we also specify an option name. For this case,
426 the code looks like this:
431 nodebuginfo, quick, detailed
434 // Enable Debug Options to be specified on the command line
435 cl::opt<DebugLev> DebugLevel("debug_level", cl::desc("Set the debugging level:"),
437 clEnumValN(nodebuginfo, "none", "disable debug information"),
438 clEnumVal(quick, "enable quick debug information"),
439 clEnumVal(detailed, "enable detailed debug information"),
442 This definition defines an enumerated command line variable of type "``enum
443 DebugLev``", which works exactly the same way as before. The difference here is
444 just the interface exposed to the user of your program and the help output by
445 the "``-help``" option:
449 USAGE: compiler [options] <input file>
452 Choose optimization level:
453 -g - No optimizations, enable debugging
454 -O1 - Enable trivial optimizations
455 -O2 - Enable default optimizations
456 -O3 - Enable expensive optimizations
457 -debug_level - Set the debugging level:
458 =none - disable debug information
459 =quick - enable quick debug information
460 =detailed - enable detailed debug information
461 -f - Enable binary output on terminals
462 -help - display available options (-help-hidden for more)
463 -o <filename> - Specify output filename
464 -quiet - Don't print informational messages
466 Again, the only structural difference between the debug level declaration and
467 the optimization level declaration is that the debug level declaration includes
468 an option name (``"debug_level"``), which automatically changes how the library
469 processes the argument. The CommandLine library supports both forms so that you
470 can choose the form most appropriate for your application.
474 Parsing a list of options
475 -------------------------
477 Now that we have the standard run-of-the-mill argument types out of the way,
478 lets get a little wild and crazy. Lets say that we want our optimizer to accept
479 a **list** of optimizations to perform, allowing duplicates. For example, we
480 might want to run: "``compiler -dce -constprop -inline -dce -strip``". In this
481 case, the order of the arguments and the number of appearances is very
482 important. This is what the "``cl::list``" template is for. First, start by
483 defining an enum of the optimizations that you would like to perform:
488 // 'inline' is a C++ keyword, so name it 'inlining'
489 dce, constprop, inlining, strip
492 Then define your "``cl::list``" variable:
496 cl::list<Opts> OptimizationList(cl::desc("Available Optimizations:"),
498 clEnumVal(dce , "Dead Code Elimination"),
499 clEnumVal(constprop , "Constant Propagation"),
500 clEnumValN(inlining, "inline", "Procedure Integration"),
501 clEnumVal(strip , "Strip Symbols"),
504 This defines a variable that is conceptually of the type
505 "``std::vector<enum Opts>``". Thus, you can access it with standard vector
510 for (unsigned i = 0; i != OptimizationList.size(); ++i)
511 switch (OptimizationList[i])
514 ... to iterate through the list of options specified.
516 Note that the "``cl::list``" template is completely general and may be used with
517 any data types or other arguments that you can use with the "``cl::opt``"
518 template. One especially useful way to use a list is to capture all of the
519 positional arguments together if there may be more than one specified. In the
520 case of a linker, for example, the linker takes several '``.o``' files, and
521 needs to capture them into a list. This is naturally specified as:
526 cl::list<std::string> InputFilenames(cl::Positional, cl::desc("<Input files>"), cl::OneOrMore);
529 This variable works just like a "``vector<string>``" object. As such, accessing
530 the list is simple, just like above. In this example, we used the
531 `cl::OneOrMore`_ modifier to inform the CommandLine library that it is an error
532 if the user does not specify any ``.o`` files on our command line. Again, this
533 just reduces the amount of checking we have to do.
535 Collecting options as a set of flags
536 ------------------------------------
538 Instead of collecting sets of options in a list, it is also possible to gather
539 information for enum values in a **bit vector**. The representation used by the
540 `cl::bits`_ class is an ``unsigned`` integer. An enum value is represented by a
541 0/1 in the enum's ordinal value bit position. 1 indicating that the enum was
542 specified, 0 otherwise. As each specified value is parsed, the resulting enum's
543 bit is set in the option's bit vector:
547 bits |= 1 << (unsigned)enum;
549 Options that are specified multiple times are redundant. Any instances after
550 the first are discarded.
552 Reworking the above list example, we could replace `cl::list`_ with `cl::bits`_:
556 cl::bits<Opts> OptimizationBits(cl::desc("Available Optimizations:"),
558 clEnumVal(dce , "Dead Code Elimination"),
559 clEnumVal(constprop , "Constant Propagation"),
560 clEnumValN(inlining, "inline", "Procedure Integration"),
561 clEnumVal(strip , "Strip Symbols"),
564 To test to see if ``constprop`` was specified, we can use the ``cl:bits::isSet``
569 if (OptimizationBits.isSet(constprop)) {
573 It's also possible to get the raw bit vector using the ``cl::bits::getBits``
578 unsigned bits = OptimizationBits.getBits();
580 Finally, if external storage is used, then the location specified must be of
581 **type** ``unsigned``. In all other ways a `cl::bits`_ option is equivalent to a
584 .. _additional extra text:
586 Adding freeform text to help output
587 -----------------------------------
589 As our program grows and becomes more mature, we may decide to put summary
590 information about what it does into the help output. The help output is styled
591 to look similar to a Unix ``man`` page, providing concise information about a
592 program. Unix ``man`` pages, however often have a description about what the
593 program does. To add this to your CommandLine program, simply pass a third
594 argument to the `cl::ParseCommandLineOptions`_ call in main. This additional
595 argument is then printed as the overview information for your program, allowing
596 you to include any additional information that you want. For example:
600 int main(int argc, char **argv) {
601 cl::ParseCommandLineOptions(argc, argv, " CommandLine compiler example\n\n"
602 " This program blah blah blah...\n");
606 would yield the help output:
610 **OVERVIEW: CommandLine compiler example
612 This program blah blah blah...**
614 USAGE: compiler [options] <input file>
618 -help - display available options (-help-hidden for more)
619 -o <filename> - Specify output filename
621 Grouping options into categories
622 --------------------------------
624 If our program has a large number of options it may become difficult for users
625 of our tool to navigate the output of ``-help``. To alleviate this problem we
626 can put our options into categories. This can be done by declaring option
627 categories (`cl::OptionCategory`_ objects) and then placing our options into
628 these categories using the `cl::cat`_ option attribute. For example:
632 cl::OptionCategory StageSelectionCat("Stage Selection Options",
633 "These control which stages are run.");
635 cl::opt<bool> Preprocessor("E",cl::desc("Run preprocessor stage."),
636 cl::cat(StageSelectionCat));
638 cl::opt<bool> NoLink("c",cl::desc("Run all stages except linking."),
639 cl::cat(StageSelectionCat));
641 The output of ``-help`` will become categorized if an option category is
642 declared. The output looks something like ::
644 OVERVIEW: This is a small program to demo the LLVM CommandLine API
645 USAGE: Sample [options]
651 -help - Display available options (-help-hidden for more)
652 -help-list - Display list of available options (-help-list-hidden for more)
655 Stage Selection Options:
656 These control which stages are run.
658 -E - Run preprocessor stage.
659 -c - Run all stages except linking.
661 In addition to the behaviour of ``-help`` changing when an option category is
662 declared, the command line option ``-help-list`` becomes visible which will
663 print the command line options as uncategorized list.
665 Note that Options that are not explicitly categorized will be placed in the
666 ``cl::GeneralCategory`` category.
673 Now that you know the basics of how to use the CommandLine library, this section
674 will give you the detailed information you need to tune how command line options
675 work, as well as information on more "advanced" command line option processing
679 .. _positional argument:
680 .. _Positional Arguments:
681 .. _Positional arguments section:
682 .. _positional options:
687 Positional arguments are those arguments that are not named, and are not
688 specified with a hyphen. Positional arguments should be used when an option is
689 specified by its position alone. For example, the standard Unix ``grep`` tool
690 takes a regular expression argument, and an optional filename to search through
691 (which defaults to standard input if a filename is not specified). Using the
692 CommandLine library, this would be specified as:
696 cl::opt<string> Regex (cl::Positional, cl::desc("<regular expression>"), cl::Required);
697 cl::opt<string> Filename(cl::Positional, cl::desc("<input file>"), cl::init("-"));
699 Given these two option declarations, the ``-help`` output for our grep
700 replacement would look like this:
704 USAGE: spiffygrep [options] <regular expression> <input file>
707 -help - display available options (-help-hidden for more)
709 ... and the resultant program could be used just like the standard ``grep``
712 Positional arguments are sorted by their order of construction. This means that
713 command line options will be ordered according to how they are listed in a .cpp
714 file, but will not have an ordering defined if the positional arguments are
715 defined in multiple .cpp files. The fix for this problem is simply to define
716 all of your positional arguments in one .cpp file.
718 Specifying positional options with hyphens
719 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
721 Sometimes you may want to specify a value to your positional argument that
722 starts with a hyphen (for example, searching for '``-foo``' in a file). At
723 first, you will have trouble doing this, because it will try to find an argument
724 named '``-foo``', and will fail (and single quotes will not save you). Note
725 that the system ``grep`` has the same problem:
729 $ spiffygrep '-foo' test.txt
730 Unknown command line argument '-foo'. Try: spiffygrep -help'
732 $ grep '-foo' test.txt
733 grep: illegal option -- f
734 grep: illegal option -- o
735 grep: illegal option -- o
736 Usage: grep -hblcnsviw pattern file . . .
738 The solution for this problem is the same for both your tool and the system
739 version: use the '``--``' marker. When the user specifies '``--``' on the
740 command line, it is telling the program that all options after the '``--``'
741 should be treated as positional arguments, not options. Thus, we can use it
746 $ spiffygrep -- -foo test.txt
749 Determining absolute position with getPosition()
750 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
752 Sometimes an option can affect or modify the meaning of another option. For
753 example, consider ``gcc``'s ``-x LANG`` option. This tells ``gcc`` to ignore the
754 suffix of subsequent positional arguments and force the file to be interpreted
755 as if it contained source code in language ``LANG``. In order to handle this
756 properly, you need to know the absolute position of each argument, especially
757 those in lists, so their interaction(s) can be applied correctly. This is also
758 useful for options like ``-llibname`` which is actually a positional argument
759 that starts with a dash.
761 So, generally, the problem is that you have two ``cl::list`` variables that
762 interact in some way. To ensure the correct interaction, you can use the
763 ``cl::list::getPosition(optnum)`` method. This method returns the absolute
764 position (as found on the command line) of the ``optnum`` item in the
767 The idiom for usage is like this:
771 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
772 static cl::list<std::string> Libraries("l", cl::ZeroOrMore);
774 int main(int argc, char**argv) {
776 std::vector<std::string>::iterator fileIt = Files.begin();
777 std::vector<std::string>::iterator libIt = Libraries.begin();
778 unsigned libPos = 0, filePos = 0;
780 if ( libIt != Libraries.end() )
781 libPos = Libraries.getPosition( libIt - Libraries.begin() );
784 if ( fileIt != Files.end() )
785 filePos = Files.getPosition( fileIt - Files.begin() );
789 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
790 // Source File Is next
793 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
798 break; // we're done with the list
802 Note that, for compatibility reasons, the ``cl::opt`` also supports an
803 ``unsigned getPosition()`` option that will provide the absolute position of
804 that option. You can apply the same approach as above with a ``cl::opt`` and a
805 ``cl::list`` option as you can with two lists.
807 .. _interpreter style options:
808 .. _cl::ConsumeAfter:
809 .. _this section for more information:
811 The ``cl::ConsumeAfter`` modifier
812 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
814 The ``cl::ConsumeAfter`` `formatting option`_ is used to construct programs that
815 use "interpreter style" option processing. With this style of option
816 processing, all arguments specified after the last positional argument are
817 treated as special interpreter arguments that are not interpreted by the command
820 As a concrete example, lets say we are developing a replacement for the standard
821 Unix Bourne shell (``/bin/sh``). To run ``/bin/sh``, first you specify options
822 to the shell itself (like ``-x`` which turns on trace output), then you specify
823 the name of the script to run, then you specify arguments to the script. These
824 arguments to the script are parsed by the Bourne shell command line option
825 processor, but are not interpreted as options to the shell itself. Using the
826 CommandLine library, we would specify this as:
830 cl::opt<string> Script(cl::Positional, cl::desc("<input script>"), cl::init("-"));
831 cl::list<string> Argv(cl::ConsumeAfter, cl::desc("<program arguments>..."));
832 cl::opt<bool> Trace("x", cl::desc("Enable trace output"));
834 which automatically provides the help output:
838 USAGE: spiffysh [options] <input script> <program arguments>...
841 -help - display available options (-help-hidden for more)
842 -x - Enable trace output
844 At runtime, if we run our new shell replacement as ```spiffysh -x test.sh -a -x
845 -y bar``', the ``Trace`` variable will be set to true, the ``Script`` variable
846 will be set to "``test.sh``", and the ``Argv`` list will contain ``["-a", "-x",
847 "-y", "bar"]``, because they were specified after the last positional argument
848 (which is the script name).
850 There are several limitations to when ``cl::ConsumeAfter`` options can be
851 specified. For example, only one ``cl::ConsumeAfter`` can be specified per
852 program, there must be at least one `positional argument`_ specified, there must
853 not be any `cl::list`_ positional arguments, and the ``cl::ConsumeAfter`` option
854 should be a `cl::list`_ option.
857 .. _Internal vs External Storage:
859 Internal vs External Storage
860 ----------------------------
862 By default, all command line options automatically hold the value that they
863 parse from the command line. This is very convenient in the common case,
864 especially when combined with the ability to define command line options in the
865 files that use them. This is called the internal storage model.
867 Sometimes, however, it is nice to separate the command line option processing
868 code from the storage of the value parsed. For example, lets say that we have a
869 '``-debug``' option that we would like to use to enable debug information across
870 the entire body of our program. In this case, the boolean value controlling the
871 debug code should be globally accessible (in a header file, for example) yet the
872 command line option processing code should not be exposed to all of these
873 clients (requiring lots of .cpp files to ``#include CommandLine.h``).
875 To do this, set up your .h file with your option, like this for example:
879 // DebugFlag.h - Get access to the '-debug' command line option
882 // DebugFlag - This boolean is set to true if the '-debug' command line option
883 // is specified. This should probably not be referenced directly, instead, use
884 // the DEBUG macro below.
886 extern bool DebugFlag;
888 // DEBUG macro - This macro should be used by code to emit debug information.
889 // In the '-debug' option is specified on the command line, and if this is a
890 // debug build, then the code specified as the option to the macro will be
891 // executed. Otherwise it will not be.
895 #define DEBUG(X) do { if (DebugFlag) { X; } } while (0)
898 This allows clients to blissfully use the ``DEBUG()`` macro, or the
899 ``DebugFlag`` explicitly if they want to. Now we just need to be able to set
900 the ``DebugFlag`` boolean when the option is set. To do this, we pass an
901 additional argument to our command line argument processor, and we specify where
902 to fill in with the `cl::location`_ attribute:
906 bool DebugFlag; // the actual value
907 static cl::opt<bool, true> // The parser
908 Debug("debug", cl::desc("Enable debug output"), cl::Hidden, cl::location(DebugFlag));
910 In the above example, we specify "``true``" as the second argument to the
911 `cl::opt`_ template, indicating that the template should not maintain a copy of
912 the value itself. In addition to this, we specify the `cl::location`_
913 attribute, so that ``DebugFlag`` is automatically set.
918 This section describes the basic attributes that you can specify on options.
920 * The option name attribute (which is required for all options, except
921 `positional options`_) specifies what the option name is. This option is
922 specified in simple double quotes:
926 cl::opt<**bool**> Quiet("quiet");
930 * The **cl::desc** attribute specifies a description for the option to be
931 shown in the ``-help`` output for the program.
935 * The **cl::value_desc** attribute specifies a string that can be used to
936 fine tune the ``-help`` output for a command line option. Look `here`_ for an
941 * The **cl::init** attribute specifies an initial value for a `scalar`_
942 option. If this attribute is not specified then the command line option value
943 defaults to the value created by the default constructor for the
948 If you specify both **cl::init** and **cl::location** for an option, you
949 must specify **cl::location** first, so that when the command-line parser
950 sees **cl::init**, it knows where to put the initial value. (You will get an
951 error at runtime if you don't put them in the right order.)
955 * The **cl::location** attribute where to store the value for a parsed command
956 line option if using external storage. See the section on `Internal vs
957 External Storage`_ for more information.
961 * The **cl::aliasopt** attribute specifies which option a `cl::alias`_ option is
966 * The **cl::values** attribute specifies the string-to-value mapping to be used
967 by the generic parser. It takes a **clEnumValEnd terminated** list of
968 (option, value, description) triplets that specify the option name, the value
969 mapped to, and the description shown in the ``-help`` for the tool. Because
970 the generic parser is used most frequently with enum values, two macros are
973 #. The **clEnumVal** macro is used as a nice simple way to specify a triplet
974 for an enum. This macro automatically makes the option name be the same as
975 the enum name. The first option to the macro is the enum, the second is
976 the description for the command line option.
978 #. The **clEnumValN** macro is used to specify macro options where the option
979 name doesn't equal the enum name. For this macro, the first argument is
980 the enum value, the second is the flag name, and the second is the
983 You will get a compile time error if you try to use cl::values with a parser
984 that does not support it.
988 * The **cl::multi_val** attribute specifies that this option takes has multiple
989 values (example: ``-sectalign segname sectname sectvalue``). This attribute
990 takes one unsigned argument - the number of values for the option. This
991 attribute is valid only on ``cl::list`` options (and will fail with compile
992 error if you try to use it with other option types). It is allowed to use all
993 of the usual modifiers on multi-valued options (besides
994 ``cl::ValueDisallowed``, obviously).
998 * The **cl::cat** attribute specifies the option category that the option
999 belongs to. The category should be a `cl::OptionCategory`_ object.
1004 Option modifiers are the flags and expressions that you pass into the
1005 constructors for `cl::opt`_ and `cl::list`_. These modifiers give you the
1006 ability to tweak how options are parsed and how ``-help`` output is generated to
1007 fit your application well.
1009 These options fall into five main categories:
1011 #. Hiding an option from ``-help`` output
1013 #. Controlling the number of occurrences required and allowed
1015 #. Controlling whether or not a value must be specified
1017 #. Controlling other formatting options
1019 #. Miscellaneous option modifiers
1021 It is not possible to specify two options from the same category (you'll get a
1022 runtime error) to a single option, except for options in the miscellaneous
1023 category. The CommandLine library specifies defaults for all of these settings
1024 that are the most useful in practice and the most common, which mean that you
1025 usually shouldn't have to worry about these.
1027 Hiding an option from ``-help`` output
1028 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1030 The ``cl::NotHidden``, ``cl::Hidden``, and ``cl::ReallyHidden`` modifiers are
1031 used to control whether or not an option appears in the ``-help`` and
1032 ``-help-hidden`` output for the compiled program:
1036 * The **cl::NotHidden** modifier (which is the default for `cl::opt`_ and
1037 `cl::list`_ options) indicates the option is to appear in both help
1042 * The **cl::Hidden** modifier (which is the default for `cl::alias`_ options)
1043 indicates that the option should not appear in the ``-help`` output, but
1044 should appear in the ``-help-hidden`` output.
1046 .. _cl::ReallyHidden:
1048 * The **cl::ReallyHidden** modifier indicates that the option should not appear
1051 Controlling the number of occurrences required and allowed
1052 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1054 This group of options is used to control how many time an option is allowed (or
1055 required) to be specified on the command line of your program. Specifying a
1056 value for this setting allows the CommandLine library to do error checking for
1059 The allowed values for this option group are:
1063 * The **cl::Optional** modifier (which is the default for the `cl::opt`_ and
1064 `cl::alias`_ classes) indicates that your program will allow either zero or
1065 one occurrence of the option to be specified.
1069 * The **cl::ZeroOrMore** modifier (which is the default for the `cl::list`_
1070 class) indicates that your program will allow the option to be specified zero
1075 * The **cl::Required** modifier indicates that the specified option must be
1076 specified exactly one time.
1080 * The **cl::OneOrMore** modifier indicates that the option must be specified at
1083 * The **cl::ConsumeAfter** modifier is described in the `Positional arguments
1086 If an option is not specified, then the value of the option is equal to the
1087 value specified by the `cl::init`_ attribute. If the ``cl::init`` attribute is
1088 not specified, the option value is initialized with the default constructor for
1091 If an option is specified multiple times for an option of the `cl::opt`_ class,
1092 only the last value will be retained.
1094 Controlling whether or not a value must be specified
1095 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1097 This group of options is used to control whether or not the option allows a
1098 value to be present. In the case of the CommandLine library, a value is either
1099 specified with an equal sign (e.g. '``-index-depth=17``') or as a trailing
1100 string (e.g. '``-o a.out``').
1102 The allowed values for this option group are:
1104 .. _cl::ValueOptional:
1106 * The **cl::ValueOptional** modifier (which is the default for ``bool`` typed
1107 options) specifies that it is acceptable to have a value, or not. A boolean
1108 argument can be enabled just by appearing on the command line, or it can have
1109 an explicit '``-foo=true``'. If an option is specified with this mode, it is
1110 illegal for the value to be provided without the equal sign. Therefore
1111 '``-foo true``' is illegal. To get this behavior, you must use
1112 the `cl::ValueRequired`_ modifier.
1114 .. _cl::ValueRequired:
1116 * The **cl::ValueRequired** modifier (which is the default for all other types
1117 except for `unnamed alternatives using the generic parser`_) specifies that a
1118 value must be provided. This mode informs the command line library that if an
1119 option is not provides with an equal sign, that the next argument provided
1120 must be the value. This allows things like '``-o a.out``' to work.
1122 .. _cl::ValueDisallowed:
1124 * The **cl::ValueDisallowed** modifier (which is the default for `unnamed
1125 alternatives using the generic parser`_) indicates that it is a runtime error
1126 for the user to specify a value. This can be provided to disallow users from
1127 providing options to boolean options (like '``-foo=true``').
1129 In general, the default values for this option group work just like you would
1130 want them to. As mentioned above, you can specify the `cl::ValueDisallowed`_
1131 modifier to a boolean argument to restrict your command line parser. These
1132 options are mostly useful when `extending the library`_.
1134 .. _formatting option:
1136 Controlling other formatting options
1137 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1139 The formatting option group is used to specify that the command line option has
1140 special abilities and is otherwise different from other command line arguments.
1141 As usual, you can only specify one of these arguments at most.
1143 .. _cl::NormalFormatting:
1145 * The **cl::NormalFormatting** modifier (which is the default all options)
1146 specifies that this option is "normal".
1150 * The **cl::Positional** modifier specifies that this is a positional argument
1151 that does not have a command line option associated with it. See the
1152 `Positional Arguments`_ section for more information.
1154 * The **cl::ConsumeAfter** modifier specifies that this option is used to
1155 capture "interpreter style" arguments. See `this section for more
1161 * The **cl::Prefix** modifier specifies that this option prefixes its value.
1162 With 'Prefix' options, the equal sign does not separate the value from the
1163 option name specified. Instead, the value is everything after the prefix,
1164 including any equal sign if present. This is useful for processing odd
1165 arguments like ``-lmalloc`` and ``-L/usr/lib`` in a linker tool or
1166 ``-DNAME=value`` in a compiler tool. Here, the '``l``', '``D``' and '``L``'
1167 options are normal string (or list) options, that have the **cl::Prefix**
1168 modifier added to allow the CommandLine library to recognize them. Note that
1169 **cl::Prefix** options must not have the **cl::ValueDisallowed** modifier
1175 * The **cl::Grouping** modifier is used to implement Unix-style tools (like
1176 ``ls``) that have lots of single letter arguments, but only require a single
1177 dash. For example, the '``ls -labF``' command actually enables four different
1178 options, all of which are single letters. Note that **cl::Grouping** options
1181 The CommandLine library does not restrict how you use the **cl::Prefix** or
1182 **cl::Grouping** modifiers, but it is possible to specify ambiguous argument
1183 settings. Thus, it is possible to have multiple letter options that are prefix
1184 or grouping options, and they will still work as designed.
1186 To do this, the CommandLine library uses a greedy algorithm to parse the input
1187 option into (potentially multiple) prefix and grouping options. The strategy
1188 basically looks like this:
1192 parse(string OrigInput) {
1194 1. string input = OrigInput;
1195 2. if (isOption(input)) return getOption(input).parse(); // Normal option
1196 3. while (!isOption(input) && !input.empty()) input.pop_back(); // Remove the last letter
1197 4. if (input.empty()) return error(); // No matching option
1198 5. if (getOption(input).isPrefix())
1199 return getOption(input).parse(input);
1200 6. while (!input.empty()) { // Must be grouping options
1201 getOption(input).parse();
1202 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());
1204 while (!isOption(input) && !input.empty()) input.pop_back();
1206 7. if (!OrigInput.empty()) error();
1210 Miscellaneous option modifiers
1211 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1213 The miscellaneous option modifiers are the only flags where you can specify more
1214 than one flag from the set: they are not mutually exclusive. These flags
1215 specify boolean properties that modify the option.
1217 .. _cl::CommaSeparated:
1219 * The **cl::CommaSeparated** modifier indicates that any commas specified for an
1220 option's value should be used to split the value up into multiple values for
1221 the option. For example, these two options are equivalent when
1222 ``cl::CommaSeparated`` is specified: "``-foo=a -foo=b -foo=c``" and
1223 "``-foo=a,b,c``". This option only makes sense to be used in a case where the
1224 option is allowed to accept one or more values (i.e. it is a `cl::list`_
1227 .. _cl::PositionalEatsArgs:
1229 * The **cl::PositionalEatsArgs** modifier (which only applies to positional
1230 arguments, and only makes sense for lists) indicates that positional argument
1231 should consume any strings after it (including strings that start with a "-")
1232 up until another recognized positional argument. For example, if you have two
1233 "eating" positional arguments, "``pos1``" and "``pos2``", the string "``-pos1
1234 -foo -bar baz -pos2 -bork``" would cause the "``-foo -bar -baz``" strings to
1235 be applied to the "``-pos1``" option and the "``-bork``" string to be applied
1236 to the "``-pos2``" option.
1240 * The **cl::Sink** modifier is used to handle unknown options. If there is at
1241 least one option with ``cl::Sink`` modifier specified, the parser passes
1242 unrecognized option strings to it as values instead of signaling an error. As
1243 with ``cl::CommaSeparated``, this modifier only makes sense with a `cl::list`_
1246 So far, these are the only three miscellaneous option modifiers.
1253 Some systems, such as certain variants of Microsoft Windows and some older
1254 Unices have a relatively low limit on command-line length. It is therefore
1255 customary to use the so-called 'response files' to circumvent this
1256 restriction. These files are mentioned on the command-line (using the "@file")
1257 syntax. The program reads these files and inserts the contents into argv,
1258 thereby working around the command-line length limits. Response files are
1259 enabled by an optional fourth argument to `cl::ParseEnvironmentOptions`_ and
1260 `cl::ParseCommandLineOptions`_.
1262 Top-Level Classes and Functions
1263 -------------------------------
1265 Despite all of the built-in flexibility, the CommandLine option library really
1266 only consists of one function `cl::ParseCommandLineOptions`_) and three main
1267 classes: `cl::opt`_, `cl::list`_, and `cl::alias`_. This section describes
1268 these three classes in detail.
1270 .. _cl::getRegisteredOptions:
1272 The ``cl::getRegisteredOptions`` function
1273 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1275 The ``cl::getRegisteredOptions`` function is designed to give a programmer
1276 access to declared non positional command line options so that how they appear
1277 in ``-help`` can be modified prior to calling `cl::ParseCommandLineOptions`_.
1278 Note this method should not be called during any static initialisation because
1279 it cannot be guaranteed that all options will have been initialised. Hence it
1280 should be called from ``main``.
1282 This function can be used to gain access to options declared in libraries that
1283 the tool writter may not have direct access to.
1285 The function retrieves a :ref:`StringMap <dss_stringmap>` that maps the option
1286 string (e.g. ``-help``) to an ``Option*``.
1288 Here is an example of how the function could be used:
1292 using namespace llvm;
1293 int main(int argc, char **argv) {
1294 cl::OptionCategory AnotherCategory("Some options");
1296 StringMap<cl::Option*> Map;
1297 cl::getRegisteredOptions(Map);
1299 //Unhide useful option and put it in a different category
1300 assert(Map.count("print-all-options") > 0);
1301 Map["print-all-options"]->setHiddenFlag(cl::NotHidden);
1302 Map["print-all-options"]->setCategory(AnotherCategory);
1304 //Hide an option we don't want to see
1305 assert(Map.count("enable-no-infs-fp-math") > 0);
1306 Map["enable-no-infs-fp-math"]->setHiddenFlag(cl::Hidden);
1308 //Change --version to --show-version
1309 assert(Map.count("version") > 0);
1310 Map["version"]->setArgStr("show-version");
1312 //Change --help description
1313 assert(Map.count("help") > 0);
1314 Map["help"]->setDescription("Shows help");
1316 cl::ParseCommandLineOptions(argc, argv, "This is a small program to demo the LLVM CommandLine API");
1321 .. _cl::ParseCommandLineOptions:
1323 The ``cl::ParseCommandLineOptions`` function
1324 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1326 The ``cl::ParseCommandLineOptions`` function is designed to be called directly
1327 from ``main``, and is used to fill in the values of all of the command line
1328 option variables once ``argc`` and ``argv`` are available.
1330 The ``cl::ParseCommandLineOptions`` function requires two parameters (``argc``
1331 and ``argv``), but may also take an optional third parameter which holds
1332 `additional extra text`_ to emit when the ``-help`` option is invoked, and a
1333 fourth boolean parameter that enables `response files`_.
1335 .. _cl::ParseEnvironmentOptions:
1337 The ``cl::ParseEnvironmentOptions`` function
1338 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1340 The ``cl::ParseEnvironmentOptions`` function has mostly the same effects as
1341 `cl::ParseCommandLineOptions`_, except that it is designed to take values for
1342 options from an environment variable, for those cases in which reading the
1343 command line is not convenient or desired. It fills in the values of all the
1344 command line option variables just like `cl::ParseCommandLineOptions`_ does.
1346 It takes four parameters: the name of the program (since ``argv`` may not be
1347 available, it can't just look in ``argv[0]``), the name of the environment
1348 variable to examine, the optional `additional extra text`_ to emit when the
1349 ``-help`` option is invoked, and the boolean switch that controls whether
1350 `response files`_ should be read.
1352 ``cl::ParseEnvironmentOptions`` will break the environment variable's value up
1353 into words and then process them using `cl::ParseCommandLineOptions`_.
1354 **Note:** Currently ``cl::ParseEnvironmentOptions`` does not support quoting, so
1355 an environment variable containing ``-option "foo bar"`` will be parsed as three
1356 words, ``-option``, ``"foo``, and ``bar"``, which is different from what you
1357 would get from the shell with the same input.
1359 The ``cl::SetVersionPrinter`` function
1360 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1362 The ``cl::SetVersionPrinter`` function is designed to be called directly from
1363 ``main`` and *before* ``cl::ParseCommandLineOptions``. Its use is optional. It
1364 simply arranges for a function to be called in response to the ``--version``
1365 option instead of having the ``CommandLine`` library print out the usual version
1366 string for LLVM. This is useful for programs that are not part of LLVM but wish
1367 to use the ``CommandLine`` facilities. Such programs should just define a small
1368 function that takes no arguments and returns ``void`` and that prints out
1369 whatever version information is appropriate for the program. Pass the address of
1370 that function to ``cl::SetVersionPrinter`` to arrange for it to be called when
1371 the ``--version`` option is given by the user.
1376 The ``cl::opt`` class
1377 ^^^^^^^^^^^^^^^^^^^^^
1379 The ``cl::opt`` class is the class used to represent scalar command line
1380 options, and is the one used most of the time. It is a templated class which
1381 can take up to three arguments (all except for the first have default values
1387 template <class DataType, bool ExternalStorage = false,
1388 class ParserClass = parser<DataType> >
1392 The first template argument specifies what underlying data type the command line
1393 argument is, and is used to select a default parser implementation. The second
1394 template argument is used to specify whether the option should contain the
1395 storage for the option (the default) or whether external storage should be used
1396 to contain the value parsed for the option (see `Internal vs External Storage`_
1397 for more information).
1399 The third template argument specifies which parser to use. The default value
1400 selects an instantiation of the ``parser`` class based on the underlying data
1401 type of the option. In general, this default works well for most applications,
1402 so this option is only used when using a `custom parser`_.
1404 .. _lists of arguments:
1407 The ``cl::list`` class
1408 ^^^^^^^^^^^^^^^^^^^^^^
1410 The ``cl::list`` class is the class used to represent a list of command line
1411 options. It too is a templated class which can take up to three arguments:
1416 template <class DataType, class Storage = bool,
1417 class ParserClass = parser<DataType> >
1421 This class works the exact same as the `cl::opt`_ class, except that the second
1422 argument is the **type** of the external storage, not a boolean value. For this
1423 class, the marker type '``bool``' is used to indicate that internal storage
1428 The ``cl::bits`` class
1429 ^^^^^^^^^^^^^^^^^^^^^^
1431 The ``cl::bits`` class is the class used to represent a list of command line
1432 options in the form of a bit vector. It is also a templated class which can
1433 take up to three arguments:
1438 template <class DataType, class Storage = bool,
1439 class ParserClass = parser<DataType> >
1443 This class works the exact same as the `cl::list`_ class, except that the second
1444 argument must be of **type** ``unsigned`` if external storage is used.
1448 The ``cl::alias`` class
1449 ^^^^^^^^^^^^^^^^^^^^^^^
1451 The ``cl::alias`` class is a nontemplated class that is used to form aliases for
1460 The `cl::aliasopt`_ attribute should be used to specify which option this is an
1461 alias for. Alias arguments default to being `cl::Hidden`_, and use the aliased
1462 options parser to do the conversion from string to data.
1466 The ``cl::extrahelp`` class
1467 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
1469 The ``cl::extrahelp`` class is a nontemplated class that allows extra help text
1470 to be printed out for the ``-help`` option.
1478 To use the extrahelp, simply construct one with a ``const char*`` parameter to
1479 the constructor. The text passed to the constructor will be printed at the
1480 bottom of the help message, verbatim. Note that multiple ``cl::extrahelp``
1481 **can** be used, but this practice is discouraged. If your tool needs to print
1482 additional help information, put all that help into a single ``cl::extrahelp``
1489 cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
1491 .. _cl::OptionCategory:
1493 The ``cl::OptionCategory`` class
1494 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1496 The ``cl::OptionCategory`` class is a simple class for declaring
1502 class OptionCategory;
1505 An option category must have a name and optionally a description which are
1506 passed to the constructor as ``const char*``.
1508 Note that declaring an option category and associating it with an option before
1509 parsing options (e.g. statically) will change the output of ``-help`` from
1510 uncategorized to categorized. If an option category is declared but not
1511 associated with an option then it will be hidden from the output of ``-help``
1512 but will be shown in the output of ``-help-hidden``.
1514 .. _different parser:
1515 .. _discussed previously:
1520 Parsers control how the string value taken from the command line is translated
1521 into a typed value, suitable for use in a C++ program. By default, the
1522 CommandLine library uses an instance of ``parser<type>`` if the command line
1523 option specifies that it uses values of type '``type``'. Because of this,
1524 custom option processing is specified with specializations of the '``parser``'
1527 The CommandLine library provides the following builtin parser specializations,
1528 which are sufficient for most applications. It can, however, also be extended to
1529 work with new data types and new ways of interpreting the same data. See the
1530 `Writing a Custom Parser`_ for more details on this type of library extension.
1535 * The generic ``parser<t>`` parser can be used to map strings values to any data
1536 type, through the use of the `cl::values`_ property, which specifies the
1537 mapping information. The most common use of this parser is for parsing enum
1538 values, which allows you to use the CommandLine library for all of the error
1539 checking to make sure that only valid enum values are specified (as opposed to
1540 accepting arbitrary strings). Despite this, however, the generic parser class
1541 can be used for any data type.
1546 * The **parser<bool> specialization** is used to convert boolean strings to a
1547 boolean value. Currently accepted strings are "``true``", "``TRUE``",
1548 "``True``", "``1``", "``false``", "``FALSE``", "``False``", and "``0``".
1550 * The **parser<boolOrDefault> specialization** is used for cases where the value
1551 is boolean, but we also need to know whether the option was specified at all.
1552 boolOrDefault is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE.
1553 This parser accepts the same strings as **``parser<bool>``**.
1557 * The **parser<string> specialization** simply stores the parsed string into the
1558 string value specified. No conversion or modification of the data is
1564 * The **parser<int> specialization** uses the C ``strtol`` function to parse the
1565 string input. As such, it will accept a decimal number (with an optional '+'
1566 or '-' prefix) which must start with a non-zero digit. It accepts octal
1567 numbers, which are identified with a '``0``' prefix digit, and hexadecimal
1568 numbers with a prefix of '``0x``' or '``0X``'.
1574 * The **parser<double>** and **parser<float> specializations** use the standard
1575 C ``strtod`` function to convert floating point strings into floating point
1576 values. As such, a broad range of string formats is supported, including
1577 exponential notation (ex: ``1.7e15``) and properly supports locales.
1579 .. _Extension Guide:
1580 .. _extending the library:
1585 Although the CommandLine library has a lot of functionality built into it
1586 already (as discussed previously), one of its true strengths lie in its
1587 extensibility. This section discusses how the CommandLine library works under
1588 the covers and illustrates how to do some simple, common, extensions.
1592 .. _Writing a Custom Parser:
1594 Writing a custom parser
1595 -----------------------
1597 One of the simplest and most common extensions is the use of a custom parser.
1598 As `discussed previously`_, parsers are the portion of the CommandLine library
1599 that turns string input from the user into a particular parsed data type,
1600 validating the input in the process.
1602 There are two ways to use a new parser:
1604 #. Specialize the `cl::parser`_ template for your custom data type.
1606 This approach has the advantage that users of your custom data type will
1607 automatically use your custom parser whenever they define an option with a
1608 value type of your data type. The disadvantage of this approach is that it
1609 doesn't work if your fundamental data type is something that is already
1612 #. Write an independent class, using it explicitly from options that need it.
1614 This approach works well in situations where you would line to parse an
1615 option using special syntax for a not-very-special data-type. The drawback
1616 of this approach is that users of your parser have to be aware that they are
1617 using your parser instead of the builtin ones.
1619 To guide the discussion, we will discuss a custom parser that accepts file
1620 sizes, specified with an optional unit after the numeric size. For example, we
1621 would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
1622 this case, the underlying data type we want to parse into is '``unsigned``'. We
1623 choose approach #2 above because we don't want to make this the default for all
1624 ``unsigned`` options.
1626 To start out, we declare our new ``FileSizeParser`` class:
1630 struct FileSizeParser : public cl::basic_parser<unsigned> {
1631 // parse - Return true on error.
1632 bool parse(cl::Option &O, const char *ArgName, const std::string &ArgValue,
1636 Our new class inherits from the ``cl::basic_parser`` template class to fill in
1637 the default, boiler plate code for us. We give it the data type that we parse
1638 into, the last argument to the ``parse`` method, so that clients of our custom
1639 parser know what object type to pass in to the parse method. (Here we declare
1640 that we parse into '``unsigned``' variables.)
1642 For most purposes, the only method that must be implemented in a custom parser
1643 is the ``parse`` method. The ``parse`` method is called whenever the option is
1644 invoked, passing in the option itself, the option name, the string to parse, and
1645 a reference to a return value. If the string to parse is not well-formed, the
1646 parser should output an error message and return true. Otherwise it should
1647 return false and set '``Val``' to the parsed value. In our example, we
1648 implement ``parse`` as:
1652 bool FileSizeParser::parse(cl::Option &O, const char *ArgName,
1653 const std::string &Arg, unsigned &Val) {
1654 const char *ArgStart = Arg.c_str();
1657 // Parse integer part, leaving 'End' pointing to the first non-integer char
1658 Val = (unsigned)strtol(ArgStart, &End, 0);
1662 case 0: return false; // No error
1663 case 'i': // Ignore the 'i' in KiB if people use that
1664 case 'b': case 'B': // Ignore B suffix
1667 case 'g': case 'G': Val *= 1024*1024*1024; break;
1668 case 'm': case 'M': Val *= 1024*1024; break;
1669 case 'k': case 'K': Val *= 1024; break;
1672 // Print an error message if unrecognized character!
1673 return O.error("'" + Arg + "' value invalid for file size argument!");
1678 This function implements a very simple parser for the kinds of strings we are
1679 interested in. Although it has some holes (it allows "``123KKK``" for example),
1680 it is good enough for this example. Note that we use the option itself to print
1681 out the error message (the ``error`` method always returns true) in order to get
1682 a nice error message (shown below). Now that we have our parser class, we can
1687 static cl::opt<unsigned, false, FileSizeParser>
1688 MFS("max-file-size", cl::desc("Maximum file size to accept"),
1689 cl::value_desc("size"));
1691 Which adds this to the output of our program:
1696 -help - display available options (-help-hidden for more)
1698 -max-file-size=<size> - Maximum file size to accept
1700 And we can test that our parse works correctly now (the test program just prints
1701 out the max-file-size argument value):
1707 $ ./test -max-file-size=123MB
1709 $ ./test -max-file-size=3G
1711 $ ./test -max-file-size=dog
1712 -max-file-size option: 'dog' value invalid for file size argument!
1714 It looks like it works. The error message that we get is nice and helpful, and
1715 we seem to accept reasonable file sizes. This wraps up the "custom parser"
1718 Exploiting external storage
1719 ---------------------------
1721 Several of the LLVM libraries define static ``cl::opt`` instances that will
1722 automatically be included in any program that links with that library. This is
1723 a feature. However, sometimes it is necessary to know the value of the command
1724 line option outside of the library. In these cases the library does or should
1725 provide an external storage location that is accessible to users of the
1726 library. Examples of this include the ``llvm::DebugFlag`` exported by the
1727 ``lib/Support/Debug.cpp`` file and the ``llvm::TimePassesIsEnabled`` flag
1728 exported by the ``lib/VMCore/PassManager.cpp`` file.
1732 TODO: complete this section
1734 .. _dynamically loaded options:
1736 Dynamically adding command line options
1740 TODO: fill in this section