1============================== 2CommandLine 2.0 Library Manual 3============================== 4 5.. contents:: 6 :local: 7 8Introduction 9============ 10 11This document describes the CommandLine argument processing library. It will 12show you how to use it, and what it can do. The CommandLine library uses a 13declarative approach to specifying the command line options that your program 14takes. By default, these options declarations implicitly hold the value parsed 15for the option declared (of course this `can be changed`_). 16 17Although there are a **lot** of command line argument parsing libraries out 18there in many different languages, none of them fit well with what I needed. By 19looking at the features and problems of other libraries, I designed the 20CommandLine library to have the following features: 21 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 27 same performance). 28 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. 33 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** 37 boilerplate code. 38 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`_ 43 trivial. 44 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. 49 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... 54 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. 58 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. 63 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. 69 70This document will hopefully let you jump in and start using CommandLine in your 71utility quickly and painlessly. Additionally it should be a simple reference 72manual to figure out how stuff works. 73 74Quick Start Guide 75================= 76 77This section of the manual runs through a simple CommandLine'ification of a 78basic compiler tool. This is intended to show you how to jump into using the 79CommandLine library in your own program, and show you some of the cool things it 80can do. 81 82To start out, you need to include the CommandLine header file into your program: 83 84.. code-block:: c++ 85 86 #include "llvm/Support/CommandLine.h" 87 88Additionally, you need to add this as the first line of your main program: 89 90.. code-block:: c++ 91 92 int main(int argc, char **argv) { 93 cl::ParseCommandLineOptions(argc, argv); 94 ... 95 } 96 97... which actually parses the arguments and fills in the variable declarations. 98 99Now that you are ready to support command line arguments, we need to tell the 100system which ones we want, and what type of arguments they are. The CommandLine 101library uses a declarative syntax to model command line arguments with the 102global variable declarations that capture the parsed values. This means that 103for every command line option that you would like to support, there should be a 104global variable declaration to capture the result. For example, in a compiler, 105we would like to support the Unix-standard '``-o <filename>``' option to specify 106where to put the output. With the CommandLine library, this is represented like 107this: 108 109.. _scalars arguments: 110.. _here: 111 112.. code-block:: c++ 113 114 cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename")); 115 116This declares a global variable "``OutputFilename``" that is used to capture the 117result of the "``o``" argument (first parameter). We specify that this is a 118simple scalar option by using the "``cl::opt``" template (as opposed to the 119"``cl::list``" template), and tell the CommandLine library that the data 120type that we are parsing is a string. 121 122The second and third parameters (which are optional) are used to specify what to 123output for the "``-help``" option. In this case, we get a line that looks like 124this: 125 126:: 127 128 USAGE: compiler [options] 129 130 OPTIONS: 131 -help - display available options (-help-hidden for more) 132 -o <filename> - Specify output filename 133 134Because we specified that the command line option should parse using the 135``string`` data type, the variable declared is automatically usable as a real 136string in all contexts that a normal C++ string object may be used. For 137example: 138 139.. code-block:: c++ 140 141 ... 142 std::ofstream Output(OutputFilename.c_str()); 143 if (Output.good()) ... 144 ... 145 146There are many different options that you can use to customize the command line 147option handling library, but the above example shows the general interface to 148these options. The options can be specified in any order, and are specified 149with helper functions like `cl::desc(...)`_, so there are no positional 150dependencies to remember. The available options are discussed in detail in the 151`Reference Guide`_. 152 153Continuing the example, we would like to have our compiler take an input 154filename as well as an output filename, but we do not want the input filename to 155be specified with a hyphen (ie, not ``-filename.c``). To support this style of 156argument, the CommandLine library allows for `positional`_ arguments to be 157specified for the program. These positional arguments are filled with command 158line parameters that are not in option form. We use this feature like this: 159 160.. code-block:: c++ 161 162 163 cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-")); 164 165This declaration indicates that the first positional argument should be treated 166as the input filename. Here we use the `cl::init`_ option to specify an initial 167value 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 169constructor for the data type is used to initialize the value). Command line 170options default to being optional, so if we would like to require that the user 171always specify an input filename, we would add the `cl::Required`_ flag, and we 172could eliminate the `cl::init`_ modifier, like this: 173 174.. code-block:: c++ 175 176 cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::Required); 177 178Again, the CommandLine library does not require the options to be specified in 179any particular order, so the above declaration is equivalent to: 180 181.. code-block:: c++ 182 183 cl::opt<string> InputFilename(cl::Positional, cl::Required, cl::desc("<input file>")); 184 185By simply adding the `cl::Required`_ flag, the CommandLine library will 186automatically issue an error if the argument is not specified, which shifts all 187of the command line option verification code out of your application into the 188library. This is just one example of how using flags can alter the default 189behaviour of the library, on a per-option basis. By adding one of the 190declarations above, the ``-help`` option synopsis is now extended to: 191 192:: 193 194 USAGE: compiler [options] <input file> 195 196 OPTIONS: 197 -help - display available options (-help-hidden for more) 198 -o <filename> - Specify output filename 199 200... indicating that an input filename is expected. 201 202Boolean Arguments 203----------------- 204 205In addition to input and output filenames, we would like the compiler example to 206support three boolean flags: "``-f``" to force writing binary output to a 207terminal, "``--quiet``" to enable quiet mode, and "``-q``" for backwards 208compatibility with some of our users. We can support these by declaring options 209of boolean type like this: 210 211.. code-block:: c++ 212 213 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); 216 217This does what you would expect: it declares three boolean variables 218("``Force``", "``Quiet``", and "``Quiet2``") to recognize these options. Note 219that the "``-q``" option is specified with the "`cl::Hidden`_" flag. This 220modifier prevents it from being shown by the standard "``-help``" output (note 221that it is still shown in the "``-help-hidden``" output). 222 223The CommandLine library uses a `different parser`_ for different data types. 224For example, in the string case, the argument passed to the option is copied 225literally into the content of the string variable... we obviously cannot do that 226in the boolean case, however, so we must use a smarter parser. In the case of 227the boolean parser, it allows no options (in which case it assigns the value of 228true to the variable), or it allows the values "``true``" or "``false``" to be 229specified, allowing any of the following inputs: 230 231:: 232 233 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 237 238... you get the idea. The `bool parser`_ just turns the string values into 239boolean 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 242specified data type. 243 244With the declarations above, "``compiler -help``" emits this: 245 246:: 247 248 USAGE: compiler [options] <input file> 249 250 OPTIONS: 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) 255 256and "``compiler -help-hidden``" prints this: 257 258:: 259 260 USAGE: compiler [options] <input file> 261 262 OPTIONS: 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) 268 269This brief example has shown you how to use the '`cl::opt`_' class to parse 270simple scalar command line arguments. In addition to simple scalar arguments, 271the CommandLine library also provides primitives to support CommandLine option 272`aliases`_, and `lists`_ of options. 273 274.. _aliases: 275 276Argument Aliases 277---------------- 278 279So far, the example works well, except for the fact that we need to check the 280quiet condition like this now: 281 282.. code-block:: c++ 283 284 ... 285 if (!Quiet && !Quiet2) printInformationalMessage(...); 286 ... 287 288... which is a real pain! Instead of defining two values for the same 289condition, 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: 291 292.. code-block:: c++ 293 294 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)); 297 298The third line (which is the only one we modified from above) defines a "``-q``" 299alias that updates the "``Quiet``" variable (as specified by the `cl::aliasopt`_ 300modifier) whenever it is specified. Because aliases do not hold state, the only 301thing the program has to query is the ``Quiet`` variable now. Another nice 302feature of aliases is that they automatically hide themselves from the ``-help`` 303output (although, again, they are still visible in the ``-help-hidden output``). 304 305Now the application code can simply use: 306 307.. code-block:: c++ 308 309 ... 310 if (!Quiet) printInformationalMessage(...); 311 ... 312 313... which is much nicer! The "`cl::alias`_" can be used to specify an 314alternative name for any variable type, and has many uses. 315 316.. _unnamed alternatives using the generic parser: 317 318Selecting an alternative from a set of possibilities 319---------------------------------------------------- 320 321So 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 323know about, like enums or '``int*``'s? 324 325The answer is that it uses a table-driven generic parser (unless you specify 326your own parser, as described in the `Extension Guide`_). This parser maps 327literal strings to whatever type is required, and requires you to tell it what 328this mapping should be. 329 330Let's say that we would like to add four optimization levels to our optimizer, 331using the standard flags "``-g``", "``-O0``", "``-O1``", and "``-O2``". We 332could easily implement this with boolean options like above, but there are 333several problems with this strategy: 334 335#. 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. 338 339#. We would have to test 4 different variables to see which ones are set. 340 341#. This doesn't map to the numeric levels that we want... so we cannot easily 342 see if some level >= "``-O1``" is enabled. 343 344To cope with these problems, we can use an enum value, and have the CommandLine 345library fill it in with the appropriate level directly, which is used like this: 346 347.. code-block:: c++ 348 349 enum OptLevel { 350 g, O1, O2, O3 351 }; 352 353 cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"), 354 cl::values( 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"))); 359 360 ... 361 if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); 362 ... 363 364This declaration defines a variable "``OptimizationLevel``" of the 365"``OptLevel``" enum type. This variable can be assigned any of the values that 366are listed in the declaration. The CommandLine library enforces that 367the user can only specify one of the options, and it ensure that only valid enum 368values can be specified. The "``clEnumVal``" macros ensure that the command 369line arguments matched the enum values. With this option added, our help output 370now is: 371 372:: 373 374 USAGE: compiler [options] <input file> 375 376 OPTIONS: 377 Choose optimization level: 378 -g - No optimizations, enable debugging 379 -O1 - Enable trivial optimizations 380 -O2 - Enable default optimizations 381 -O3 - Enable expensive optimizations 382 -f - Enable binary output on terminals 383 -help - display available options (-help-hidden for more) 384 -o <filename> - Specify output filename 385 -quiet - Don't print informational messages 386 387In this case, it is sort of awkward that flag names correspond directly to enum 388names, because we probably don't want a enum definition named "``g``" in our 389program. Because of this, we can alternatively write this example like this: 390 391.. code-block:: c++ 392 393 enum OptLevel { 394 Debug, O1, O2, O3 395 }; 396 397 cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"), 398 cl::values( 399 clEnumValN(Debug, "g", "No optimizations, enable debugging"), 400 clEnumVal(O1 , "Enable trivial optimizations"), 401 clEnumVal(O2 , "Enable default optimizations"), 402 clEnumVal(O3 , "Enable expensive optimizations"))); 403 404 ... 405 if (OptimizationLevel == Debug) outputDebugInfo(...); 406 ... 407 408By using the "``clEnumValN``" macro instead of "``clEnumVal``", we can directly 409specify the name that the flag should get. In general a direct mapping is nice, 410but sometimes you can't or don't want to preserve the mapping, which is when you 411would use it. 412 413Named Alternatives 414------------------ 415 416Another useful argument form is a named alternative style. We shall use this 417style in our compiler to specify different debug levels that can be used. 418Instead of each debug level being its own switch, we want to support the 419following options, of which only one can be specified at a time: 420"``--debug-level=none``", "``--debug-level=quick``", 421"``--debug-level=detailed``". To do this, we use the exact same format as our 422optimization level flags, but we also specify an option name. For this case, 423the code looks like this: 424 425.. code-block:: c++ 426 427 enum DebugLev { 428 nodebuginfo, quick, detailed 429 }; 430 431 // Enable Debug Options to be specified on the command line 432 cl::opt<DebugLev> DebugLevel("debug_level", cl::desc("Set the debugging level:"), 433 cl::values( 434 clEnumValN(nodebuginfo, "none", "disable debug information"), 435 clEnumVal(quick, "enable quick debug information"), 436 clEnumVal(detailed, "enable detailed debug information"))); 437 438This definition defines an enumerated command line variable of type "``enum 439DebugLev``", which works exactly the same way as before. The difference here is 440just the interface exposed to the user of your program and the help output by 441the "``-help``" option: 442 443:: 444 445 USAGE: compiler [options] <input file> 446 447 OPTIONS: 448 Choose optimization level: 449 -g - No optimizations, enable debugging 450 -O1 - Enable trivial optimizations 451 -O2 - Enable default optimizations 452 -O3 - Enable expensive optimizations 453 -debug_level - Set the debugging level: 454 =none - disable debug information 455 =quick - enable quick debug information 456 =detailed - enable detailed debug information 457 -f - Enable binary output on terminals 458 -help - display available options (-help-hidden for more) 459 -o <filename> - Specify output filename 460 -quiet - Don't print informational messages 461 462Again, the only structural difference between the debug level declaration and 463the optimization level declaration is that the debug level declaration includes 464an option name (``"debug_level"``), which automatically changes how the library 465processes the argument. The CommandLine library supports both forms so that you 466can choose the form most appropriate for your application. 467 468.. _lists: 469 470Parsing a list of options 471------------------------- 472 473Now that we have the standard run-of-the-mill argument types out of the way, 474lets get a little wild and crazy. Lets say that we want our optimizer to accept 475a **list** of optimizations to perform, allowing duplicates. For example, we 476might want to run: "``compiler -dce -constprop -inline -dce -strip``". In this 477case, the order of the arguments and the number of appearances is very 478important. This is what the "``cl::list``" template is for. First, start by 479defining an enum of the optimizations that you would like to perform: 480 481.. code-block:: c++ 482 483 enum Opts { 484 // 'inline' is a C++ keyword, so name it 'inlining' 485 dce, constprop, inlining, strip 486 }; 487 488Then define your "``cl::list``" variable: 489 490.. code-block:: c++ 491 492 cl::list<Opts> OptimizationList(cl::desc("Available Optimizations:"), 493 cl::values( 494 clEnumVal(dce , "Dead Code Elimination"), 495 clEnumVal(constprop , "Constant Propagation"), 496 clEnumValN(inlining, "inline", "Procedure Integration"), 497 clEnumVal(strip , "Strip Symbols"))); 498 499This defines a variable that is conceptually of the type 500"``std::vector<enum Opts>``". Thus, you can access it with standard vector 501methods: 502 503.. code-block:: c++ 504 505 for (unsigned i = 0; i != OptimizationList.size(); ++i) 506 switch (OptimizationList[i]) 507 ... 508 509... to iterate through the list of options specified. 510 511Note that the "``cl::list``" template is completely general and may be used with 512any data types or other arguments that you can use with the "``cl::opt``" 513template. One especially useful way to use a list is to capture all of the 514positional arguments together if there may be more than one specified. In the 515case of a linker, for example, the linker takes several '``.o``' files, and 516needs to capture them into a list. This is naturally specified as: 517 518.. code-block:: c++ 519 520 ... 521 cl::list<std::string> InputFilenames(cl::Positional, cl::desc("<Input files>"), cl::OneOrMore); 522 ... 523 524This variable works just like a "``vector<string>``" object. As such, accessing 525the list is simple, just like above. In this example, we used the 526`cl::OneOrMore`_ modifier to inform the CommandLine library that it is an error 527if the user does not specify any ``.o`` files on our command line. Again, this 528just reduces the amount of checking we have to do. 529 530Collecting options as a set of flags 531------------------------------------ 532 533Instead of collecting sets of options in a list, it is also possible to gather 534information for enum values in a **bit vector**. The representation used by the 535`cl::bits`_ class is an ``unsigned`` integer. An enum value is represented by a 5360/1 in the enum's ordinal value bit position. 1 indicating that the enum was 537specified, 0 otherwise. As each specified value is parsed, the resulting enum's 538bit is set in the option's bit vector: 539 540.. code-block:: c++ 541 542 bits |= 1 << (unsigned)enum; 543 544Options that are specified multiple times are redundant. Any instances after 545the first are discarded. 546 547Reworking the above list example, we could replace `cl::list`_ with `cl::bits`_: 548 549.. code-block:: c++ 550 551 cl::bits<Opts> OptimizationBits(cl::desc("Available Optimizations:"), 552 cl::values( 553 clEnumVal(dce , "Dead Code Elimination"), 554 clEnumVal(constprop , "Constant Propagation"), 555 clEnumValN(inlining, "inline", "Procedure Integration"), 556 clEnumVal(strip , "Strip Symbols"))); 557 558To test to see if ``constprop`` was specified, we can use the ``cl:bits::isSet`` 559function: 560 561.. code-block:: c++ 562 563 if (OptimizationBits.isSet(constprop)) { 564 ... 565 } 566 567It's also possible to get the raw bit vector using the ``cl::bits::getBits`` 568function: 569 570.. code-block:: c++ 571 572 unsigned bits = OptimizationBits.getBits(); 573 574Finally, if external storage is used, then the location specified must be of 575**type** ``unsigned``. In all other ways a `cl::bits`_ option is equivalent to a 576`cl::list`_ option. 577 578.. _additional extra text: 579 580Adding freeform text to help output 581----------------------------------- 582 583As our program grows and becomes more mature, we may decide to put summary 584information about what it does into the help output. The help output is styled 585to look similar to a Unix ``man`` page, providing concise information about a 586program. Unix ``man`` pages, however often have a description about what the 587program does. To add this to your CommandLine program, simply pass a third 588argument to the `cl::ParseCommandLineOptions`_ call in main. This additional 589argument is then printed as the overview information for your program, allowing 590you to include any additional information that you want. For example: 591 592.. code-block:: c++ 593 594 int main(int argc, char **argv) { 595 cl::ParseCommandLineOptions(argc, argv, " CommandLine compiler example\n\n" 596 " This program blah blah blah...\n"); 597 ... 598 } 599 600would yield the help output: 601 602:: 603 604 **OVERVIEW: CommandLine compiler example 605 606 This program blah blah blah...** 607 608 USAGE: compiler [options] <input file> 609 610 OPTIONS: 611 ... 612 -help - display available options (-help-hidden for more) 613 -o <filename> - Specify output filename 614 615.. _grouping options into categories: 616 617Grouping options into categories 618-------------------------------- 619 620If our program has a large number of options it may become difficult for users 621of our tool to navigate the output of ``-help``. To alleviate this problem we 622can put our options into categories. This can be done by declaring option 623categories (`cl::OptionCategory`_ objects) and then placing our options into 624these categories using the `cl::cat`_ option attribute. For example: 625 626.. code-block:: c++ 627 628 cl::OptionCategory StageSelectionCat("Stage Selection Options", 629 "These control which stages are run."); 630 631 cl::opt<bool> Preprocessor("E",cl::desc("Run preprocessor stage."), 632 cl::cat(StageSelectionCat)); 633 634 cl::opt<bool> NoLink("c",cl::desc("Run all stages except linking."), 635 cl::cat(StageSelectionCat)); 636 637The output of ``-help`` will become categorized if an option category is 638declared. The output looks something like :: 639 640 OVERVIEW: This is a small program to demo the LLVM CommandLine API 641 USAGE: Sample [options] 642 643 OPTIONS: 644 645 General options: 646 647 -help - Display available options (-help-hidden for more) 648 -help-list - Display list of available options (-help-list-hidden for more) 649 650 651 Stage Selection Options: 652 These control which stages are run. 653 654 -E - Run preprocessor stage. 655 -c - Run all stages except linking. 656 657In addition to the behaviour of ``-help`` changing when an option category is 658declared, the command line option ``-help-list`` becomes visible which will 659print the command line options as uncategorized list. 660 661Note that Options that are not explicitly categorized will be placed in the 662``cl::GeneralCategory`` category. 663 664.. _Reference Guide: 665 666Reference Guide 667=============== 668 669Now that you know the basics of how to use the CommandLine library, this section 670will give you the detailed information you need to tune how command line options 671work, as well as information on more "advanced" command line option processing 672capabilities. 673 674.. _positional: 675.. _positional argument: 676.. _Positional Arguments: 677.. _Positional arguments section: 678.. _positional options: 679 680Positional Arguments 681-------------------- 682 683Positional arguments are those arguments that are not named, and are not 684specified with a hyphen. Positional arguments should be used when an option is 685specified by its position alone. For example, the standard Unix ``grep`` tool 686takes a regular expression argument, and an optional filename to search through 687(which defaults to standard input if a filename is not specified). Using the 688CommandLine library, this would be specified as: 689 690.. code-block:: c++ 691 692 cl::opt<string> Regex (cl::Positional, cl::desc("<regular expression>"), cl::Required); 693 cl::opt<string> Filename(cl::Positional, cl::desc("<input file>"), cl::init("-")); 694 695Given these two option declarations, the ``-help`` output for our grep 696replacement would look like this: 697 698:: 699 700 USAGE: spiffygrep [options] <regular expression> <input file> 701 702 OPTIONS: 703 -help - display available options (-help-hidden for more) 704 705... and the resultant program could be used just like the standard ``grep`` 706tool. 707 708Positional arguments are sorted by their order of construction. This means that 709command line options will be ordered according to how they are listed in a .cpp 710file, but will not have an ordering defined if the positional arguments are 711defined in multiple .cpp files. The fix for this problem is simply to define 712all of your positional arguments in one .cpp file. 713 714Specifying positional options with hyphens 715^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 716 717Sometimes you may want to specify a value to your positional argument that 718starts with a hyphen (for example, searching for '``-foo``' in a file). At 719first, you will have trouble doing this, because it will try to find an argument 720named '``-foo``', and will fail (and single quotes will not save you). Note 721that the system ``grep`` has the same problem: 722 723:: 724 725 $ spiffygrep '-foo' test.txt 726 Unknown command line argument '-foo'. Try: spiffygrep -help' 727 728 $ grep '-foo' test.txt 729 grep: illegal option -- f 730 grep: illegal option -- o 731 grep: illegal option -- o 732 Usage: grep -hblcnsviw pattern file . . . 733 734The solution for this problem is the same for both your tool and the system 735version: use the '``--``' marker. When the user specifies '``--``' on the 736command line, it is telling the program that all options after the '``--``' 737should be treated as positional arguments, not options. Thus, we can use it 738like this: 739 740:: 741 742 $ spiffygrep -- -foo test.txt 743 ...output... 744 745Determining absolute position with getPosition() 746^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 747 748Sometimes an option can affect or modify the meaning of another option. For 749example, consider ``gcc``'s ``-x LANG`` option. This tells ``gcc`` to ignore the 750suffix of subsequent positional arguments and force the file to be interpreted 751as if it contained source code in language ``LANG``. In order to handle this 752properly, you need to know the absolute position of each argument, especially 753those in lists, so their interaction(s) can be applied correctly. This is also 754useful for options like ``-llibname`` which is actually a positional argument 755that starts with a dash. 756 757So, generally, the problem is that you have two ``cl::list`` variables that 758interact in some way. To ensure the correct interaction, you can use the 759``cl::list::getPosition(optnum)`` method. This method returns the absolute 760position (as found on the command line) of the ``optnum`` item in the 761``cl::list``. 762 763The idiom for usage is like this: 764 765.. code-block:: c++ 766 767 static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); 768 static cl::list<std::string> Libraries("l", cl::ZeroOrMore); 769 770 int main(int argc, char**argv) { 771 // ... 772 std::vector<std::string>::iterator fileIt = Files.begin(); 773 std::vector<std::string>::iterator libIt = Libraries.begin(); 774 unsigned libPos = 0, filePos = 0; 775 while ( 1 ) { 776 if ( libIt != Libraries.end() ) 777 libPos = Libraries.getPosition( libIt - Libraries.begin() ); 778 else 779 libPos = 0; 780 if ( fileIt != Files.end() ) 781 filePos = Files.getPosition( fileIt - Files.begin() ); 782 else 783 filePos = 0; 784 785 if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) { 786 // Source File Is next 787 ++fileIt; 788 } 789 else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) { 790 // Library is next 791 ++libIt; 792 } 793 else 794 break; // we're done with the list 795 } 796 } 797 798Note that, for compatibility reasons, the ``cl::opt`` also supports an 799``unsigned getPosition()`` option that will provide the absolute position of 800that option. You can apply the same approach as above with a ``cl::opt`` and a 801``cl::list`` option as you can with two lists. 802 803.. _interpreter style options: 804.. _cl::ConsumeAfter: 805.. _this section for more information: 806 807The ``cl::ConsumeAfter`` modifier 808^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 809 810The ``cl::ConsumeAfter`` `formatting option`_ is used to construct programs that 811use "interpreter style" option processing. With this style of option 812processing, all arguments specified after the last positional argument are 813treated as special interpreter arguments that are not interpreted by the command 814line argument. 815 816As a concrete example, lets say we are developing a replacement for the standard 817Unix Bourne shell (``/bin/sh``). To run ``/bin/sh``, first you specify options 818to the shell itself (like ``-x`` which turns on trace output), then you specify 819the name of the script to run, then you specify arguments to the script. These 820arguments to the script are parsed by the Bourne shell command line option 821processor, but are not interpreted as options to the shell itself. Using the 822CommandLine library, we would specify this as: 823 824.. code-block:: c++ 825 826 cl::opt<string> Script(cl::Positional, cl::desc("<input script>"), cl::init("-")); 827 cl::list<string> Argv(cl::ConsumeAfter, cl::desc("<program arguments>...")); 828 cl::opt<bool> Trace("x", cl::desc("Enable trace output")); 829 830which automatically provides the help output: 831 832:: 833 834 USAGE: spiffysh [options] <input script> <program arguments>... 835 836 OPTIONS: 837 -help - display available options (-help-hidden for more) 838 -x - Enable trace output 839 840At runtime, if we run our new shell replacement as ```spiffysh -x test.sh -a -x 841-y bar``', the ``Trace`` variable will be set to true, the ``Script`` variable 842will be set to "``test.sh``", and the ``Argv`` list will contain ``["-a", "-x", 843"-y", "bar"]``, because they were specified after the last positional argument 844(which is the script name). 845 846There are several limitations to when ``cl::ConsumeAfter`` options can be 847specified. For example, only one ``cl::ConsumeAfter`` can be specified per 848program, there must be at least one `positional argument`_ specified, there must 849not be any `cl::list`_ positional arguments, and the ``cl::ConsumeAfter`` option 850should be a `cl::list`_ option. 851 852.. _can be changed: 853.. _Internal vs External Storage: 854 855Internal vs External Storage 856---------------------------- 857 858By default, all command line options automatically hold the value that they 859parse from the command line. This is very convenient in the common case, 860especially when combined with the ability to define command line options in the 861files that use them. This is called the internal storage model. 862 863Sometimes, however, it is nice to separate the command line option processing 864code from the storage of the value parsed. For example, lets say that we have a 865'``-debug``' option that we would like to use to enable debug information across 866the entire body of our program. In this case, the boolean value controlling the 867debug code should be globally accessible (in a header file, for example) yet the 868command line option processing code should not be exposed to all of these 869clients (requiring lots of .cpp files to ``#include CommandLine.h``). 870 871To do this, set up your .h file with your option, like this for example: 872 873.. code-block:: c++ 874 875 // DebugFlag.h - Get access to the '-debug' command line option 876 // 877 878 // DebugFlag - This boolean is set to true if the '-debug' command line option 879 // is specified. This should probably not be referenced directly, instead, use 880 // the DEBUG macro below. 881 // 882 extern bool DebugFlag; 883 884 // DEBUG macro - This macro should be used by code to emit debug information. 885 // In the '-debug' option is specified on the command line, and if this is a 886 // debug build, then the code specified as the option to the macro will be 887 // executed. Otherwise it will not be. 888 #ifdef NDEBUG 889 #define LLVM_DEBUG(X) 890 #else 891 #define LLVM_DEBUG(X) do { if (DebugFlag) { X; } } while (0) 892 #endif 893 894This allows clients to blissfully use the ``LLVM_DEBUG()`` macro, or the 895``DebugFlag`` explicitly if they want to. Now we just need to be able to set 896the ``DebugFlag`` boolean when the option is set. To do this, we pass an 897additional argument to our command line argument processor, and we specify where 898to fill in with the `cl::location`_ attribute: 899 900.. code-block:: c++ 901 902 bool DebugFlag; // the actual value 903 static cl::opt<bool, true> // The parser 904 Debug("debug", cl::desc("Enable debug output"), cl::Hidden, cl::location(DebugFlag)); 905 906In the above example, we specify "``true``" as the second argument to the 907`cl::opt`_ template, indicating that the template should not maintain a copy of 908the value itself. In addition to this, we specify the `cl::location`_ 909attribute, so that ``DebugFlag`` is automatically set. 910 911Option Attributes 912----------------- 913 914This section describes the basic attributes that you can specify on options. 915 916* The option name attribute (which is required for all options, except 917 `positional options`_) specifies what the option name is. This option is 918 specified in simple double quotes: 919 920 .. code-block:: c++ 921 922 cl::opt<bool> Quiet("quiet"); 923 924.. _cl::desc(...): 925 926* The **cl::desc** attribute specifies a description for the option to be 927 shown in the ``-help`` output for the program. This attribute supports 928 multi-line descriptions with lines separated by '\n'. 929 930.. _cl::value_desc: 931 932* The **cl::value_desc** attribute specifies a string that can be used to 933 fine tune the ``-help`` output for a command line option. Look `here`_ for an 934 example. 935 936.. _cl::init: 937 938* The **cl::init** attribute specifies an initial value for a `scalar`_ 939 option. If this attribute is not specified then the command line option value 940 defaults to the value created by the default constructor for the 941 type. 942 943 .. warning:: 944 945 If you specify both **cl::init** and **cl::location** for an option, you 946 must specify **cl::location** first, so that when the command-line parser 947 sees **cl::init**, it knows where to put the initial value. (You will get an 948 error at runtime if you don't put them in the right order.) 949 950.. _cl::location: 951 952* The **cl::location** attribute where to store the value for a parsed command 953 line option if using external storage. See the section on `Internal vs 954 External Storage`_ for more information. 955 956.. _cl::aliasopt: 957 958* The **cl::aliasopt** attribute specifies which option a `cl::alias`_ option is 959 an alias for. 960 961.. _cl::values: 962 963* The **cl::values** attribute specifies the string-to-value mapping to be used 964 by the generic parser. It takes a list of (option, value, description) 965 triplets that specify the option name, the value mapped to, and the 966 description shown in the ``-help`` for the tool. Because the generic parser 967 is used most frequently with enum values, two macros are often useful: 968 969 #. The **clEnumVal** macro is used as a nice simple way to specify a triplet 970 for an enum. This macro automatically makes the option name be the same as 971 the enum name. The first option to the macro is the enum, the second is 972 the description for the command line option. 973 974 #. The **clEnumValN** macro is used to specify macro options where the option 975 name doesn't equal the enum name. For this macro, the first argument is 976 the enum value, the second is the flag name, and the second is the 977 description. 978 979 You will get a compile time error if you try to use cl::values with a parser 980 that does not support it. 981 982.. _cl::multi_val: 983 984* The **cl::multi_val** attribute specifies that this option takes has multiple 985 values (example: ``-sectalign segname sectname sectvalue``). This attribute 986 takes one unsigned argument - the number of values for the option. This 987 attribute is valid only on ``cl::list`` options (and will fail with compile 988 error if you try to use it with other option types). It is allowed to use all 989 of the usual modifiers on multi-valued options (besides 990 ``cl::ValueDisallowed``, obviously). 991 992.. _cl::cat: 993 994* The **cl::cat** attribute specifies the option category that the option 995 belongs to. The category should be a `cl::OptionCategory`_ object. 996 997Option Modifiers 998---------------- 999 1000Option modifiers are the flags and expressions that you pass into the 1001constructors for `cl::opt`_ and `cl::list`_. These modifiers give you the 1002ability to tweak how options are parsed and how ``-help`` output is generated to 1003fit your application well. 1004 1005These options fall into five main categories: 1006 1007#. Hiding an option from ``-help`` output 1008 1009#. Controlling the number of occurrences required and allowed 1010 1011#. Controlling whether or not a value must be specified 1012 1013#. Controlling other formatting options 1014 1015#. Miscellaneous option modifiers 1016 1017It is not possible to specify two options from the same category (you'll get a 1018runtime error) to a single option, except for options in the miscellaneous 1019category. The CommandLine library specifies defaults for all of these settings 1020that are the most useful in practice and the most common, which mean that you 1021usually shouldn't have to worry about these. 1022 1023Hiding an option from ``-help`` output 1024^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1025 1026The ``cl::NotHidden``, ``cl::Hidden``, and ``cl::ReallyHidden`` modifiers are 1027used to control whether or not an option appears in the ``-help`` and 1028``-help-hidden`` output for the compiled program: 1029 1030.. _cl::NotHidden: 1031 1032* The **cl::NotHidden** modifier (which is the default for `cl::opt`_ and 1033 `cl::list`_ options) indicates the option is to appear in both help 1034 listings. 1035 1036.. _cl::Hidden: 1037 1038* The **cl::Hidden** modifier (which is the default for `cl::alias`_ options) 1039 indicates that the option should not appear in the ``-help`` output, but 1040 should appear in the ``-help-hidden`` output. 1041 1042.. _cl::ReallyHidden: 1043 1044* The **cl::ReallyHidden** modifier indicates that the option should not appear 1045 in any help output. 1046 1047Controlling the number of occurrences required and allowed 1048^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1049 1050This group of options is used to control how many time an option is allowed (or 1051required) to be specified on the command line of your program. Specifying a 1052value for this setting allows the CommandLine library to do error checking for 1053you. 1054 1055The allowed values for this option group are: 1056 1057.. _cl::Optional: 1058 1059* The **cl::Optional** modifier (which is the default for the `cl::opt`_ and 1060 `cl::alias`_ classes) indicates that your program will allow either zero or 1061 one occurrence of the option to be specified. 1062 1063.. _cl::ZeroOrMore: 1064 1065* The **cl::ZeroOrMore** modifier (which is the default for the `cl::list`_ 1066 class) indicates that your program will allow the option to be specified zero 1067 or more times. 1068 1069.. _cl::Required: 1070 1071* The **cl::Required** modifier indicates that the specified option must be 1072 specified exactly one time. 1073 1074.. _cl::OneOrMore: 1075 1076* The **cl::OneOrMore** modifier indicates that the option must be specified at 1077 least one time. 1078 1079* The **cl::ConsumeAfter** modifier is described in the `Positional arguments 1080 section`_. 1081 1082If an option is not specified, then the value of the option is equal to the 1083value specified by the `cl::init`_ attribute. If the ``cl::init`` attribute is 1084not specified, the option value is initialized with the default constructor for 1085the data type. 1086 1087If an option is specified multiple times for an option of the `cl::opt`_ class, 1088only the last value will be retained. 1089 1090Controlling whether or not a value must be specified 1091^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1092 1093This group of options is used to control whether or not the option allows a 1094value to be present. In the case of the CommandLine library, a value is either 1095specified with an equal sign (e.g. '``-index-depth=17``') or as a trailing 1096string (e.g. '``-o a.out``'). 1097 1098The allowed values for this option group are: 1099 1100.. _cl::ValueOptional: 1101 1102* The **cl::ValueOptional** modifier (which is the default for ``bool`` typed 1103 options) specifies that it is acceptable to have a value, or not. A boolean 1104 argument can be enabled just by appearing on the command line, or it can have 1105 an explicit '``-foo=true``'. If an option is specified with this mode, it is 1106 illegal for the value to be provided without the equal sign. Therefore 1107 '``-foo true``' is illegal. To get this behavior, you must use 1108 the `cl::ValueRequired`_ modifier. 1109 1110.. _cl::ValueRequired: 1111 1112* The **cl::ValueRequired** modifier (which is the default for all other types 1113 except for `unnamed alternatives using the generic parser`_) specifies that a 1114 value must be provided. This mode informs the command line library that if an 1115 option is not provides with an equal sign, that the next argument provided 1116 must be the value. This allows things like '``-o a.out``' to work. 1117 1118.. _cl::ValueDisallowed: 1119 1120* The **cl::ValueDisallowed** modifier (which is the default for `unnamed 1121 alternatives using the generic parser`_) indicates that it is a runtime error 1122 for the user to specify a value. This can be provided to disallow users from 1123 providing options to boolean options (like '``-foo=true``'). 1124 1125In general, the default values for this option group work just like you would 1126want them to. As mentioned above, you can specify the `cl::ValueDisallowed`_ 1127modifier to a boolean argument to restrict your command line parser. These 1128options are mostly useful when `extending the library`_. 1129 1130.. _formatting option: 1131 1132Controlling other formatting options 1133^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1134 1135The formatting option group is used to specify that the command line option has 1136special abilities and is otherwise different from other command line arguments. 1137As usual, you can only specify one of these arguments at most. 1138 1139.. _cl::NormalFormatting: 1140 1141* The **cl::NormalFormatting** modifier (which is the default all options) 1142 specifies that this option is "normal". 1143 1144.. _cl::Positional: 1145 1146* The **cl::Positional** modifier specifies that this is a positional argument 1147 that does not have a command line option associated with it. See the 1148 `Positional Arguments`_ section for more information. 1149 1150* The **cl::ConsumeAfter** modifier specifies that this option is used to 1151 capture "interpreter style" arguments. See `this section for more 1152 information`_. 1153 1154.. _prefix: 1155.. _cl::Prefix: 1156 1157* The **cl::Prefix** modifier specifies that this option prefixes its value. 1158 With 'Prefix' options, the equal sign does not separate the value from the 1159 option name specified. Instead, the value is everything after the prefix, 1160 including any equal sign if present. This is useful for processing odd 1161 arguments like ``-lmalloc`` and ``-L/usr/lib`` in a linker tool or 1162 ``-DNAME=value`` in a compiler tool. Here, the '``l``', '``D``' and '``L``' 1163 options are normal string (or list) options, that have the **cl::Prefix** 1164 modifier added to allow the CommandLine library to recognize them. Note that 1165 **cl::Prefix** options must not have the **cl::ValueDisallowed** modifier 1166 specified. 1167 1168.. _grouping: 1169.. _cl::Grouping: 1170 1171* The **cl::Grouping** modifier is used to implement Unix-style tools (like 1172 ``ls``) that have lots of single letter arguments, but only require a single 1173 dash. For example, the '``ls -labF``' command actually enables four different 1174 options, all of which are single letters. Note that **cl::Grouping** options 1175 cannot have values. 1176 1177The CommandLine library does not restrict how you use the **cl::Prefix** or 1178**cl::Grouping** modifiers, but it is possible to specify ambiguous argument 1179settings. Thus, it is possible to have multiple letter options that are prefix 1180or grouping options, and they will still work as designed. 1181 1182To do this, the CommandLine library uses a greedy algorithm to parse the input 1183option into (potentially multiple) prefix and grouping options. The strategy 1184basically looks like this: 1185 1186:: 1187 1188 parse(string OrigInput) { 1189 1190 1. string input = OrigInput; 1191 2. if (isOption(input)) return getOption(input).parse(); // Normal option 1192 3. while (!isOption(input) && !input.empty()) input.pop_back(); // Remove the last letter 1193 4. if (input.empty()) return error(); // No matching option 1194 5. if (getOption(input).isPrefix()) 1195 return getOption(input).parse(input); 1196 6. while (!input.empty()) { // Must be grouping options 1197 getOption(input).parse(); 1198 OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length()); 1199 input = OrigInput; 1200 while (!isOption(input) && !input.empty()) input.pop_back(); 1201 } 1202 7. if (!OrigInput.empty()) error(); 1203 1204 } 1205 1206Miscellaneous option modifiers 1207^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1208 1209The miscellaneous option modifiers are the only flags where you can specify more 1210than one flag from the set: they are not mutually exclusive. These flags 1211specify boolean properties that modify the option. 1212 1213.. _cl::CommaSeparated: 1214 1215* The **cl::CommaSeparated** modifier indicates that any commas specified for an 1216 option's value should be used to split the value up into multiple values for 1217 the option. For example, these two options are equivalent when 1218 ``cl::CommaSeparated`` is specified: "``-foo=a -foo=b -foo=c``" and 1219 "``-foo=a,b,c``". This option only makes sense to be used in a case where the 1220 option is allowed to accept one or more values (i.e. it is a `cl::list`_ 1221 option). 1222 1223.. _cl::PositionalEatsArgs: 1224 1225* The **cl::PositionalEatsArgs** modifier (which only applies to positional 1226 arguments, and only makes sense for lists) indicates that positional argument 1227 should consume any strings after it (including strings that start with a "-") 1228 up until another recognized positional argument. For example, if you have two 1229 "eating" positional arguments, "``pos1``" and "``pos2``", the string "``-pos1 1230 -foo -bar baz -pos2 -bork``" would cause the "``-foo -bar -baz``" strings to 1231 be applied to the "``-pos1``" option and the "``-bork``" string to be applied 1232 to the "``-pos2``" option. 1233 1234.. _cl::Sink: 1235 1236* The **cl::Sink** modifier is used to handle unknown options. If there is at 1237 least one option with ``cl::Sink`` modifier specified, the parser passes 1238 unrecognized option strings to it as values instead of signaling an error. As 1239 with ``cl::CommaSeparated``, this modifier only makes sense with a `cl::list`_ 1240 option. 1241 1242So far, these are the only three miscellaneous option modifiers. 1243 1244.. _response files: 1245 1246Response files 1247^^^^^^^^^^^^^^ 1248 1249Some systems, such as certain variants of Microsoft Windows and some older 1250Unices have a relatively low limit on command-line length. It is therefore 1251customary to use the so-called 'response files' to circumvent this 1252restriction. These files are mentioned on the command-line (using the "@file") 1253syntax. The program reads these files and inserts the contents into argv, 1254thereby working around the command-line length limits. 1255 1256Top-Level Classes and Functions 1257------------------------------- 1258 1259Despite all of the built-in flexibility, the CommandLine option library really 1260only consists of one function `cl::ParseCommandLineOptions`_) and three main 1261classes: `cl::opt`_, `cl::list`_, and `cl::alias`_. This section describes 1262these three classes in detail. 1263 1264.. _cl::getRegisteredOptions: 1265 1266The ``cl::getRegisteredOptions`` function 1267^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1268 1269The ``cl::getRegisteredOptions`` function is designed to give a programmer 1270access to declared non-positional command line options so that how they appear 1271in ``-help`` can be modified prior to calling `cl::ParseCommandLineOptions`_. 1272Note this method should not be called during any static initialisation because 1273it cannot be guaranteed that all options will have been initialised. Hence it 1274should be called from ``main``. 1275 1276This function can be used to gain access to options declared in libraries that 1277the tool writter may not have direct access to. 1278 1279The function retrieves a :ref:`StringMap <dss_stringmap>` that maps the option 1280string (e.g. ``-help``) to an ``Option*``. 1281 1282Here is an example of how the function could be used: 1283 1284.. code-block:: c++ 1285 1286 using namespace llvm; 1287 int main(int argc, char **argv) { 1288 cl::OptionCategory AnotherCategory("Some options"); 1289 1290 StringMap<cl::Option*> &Map = cl::getRegisteredOptions(); 1291 1292 //Unhide useful option and put it in a different category 1293 assert(Map.count("print-all-options") > 0); 1294 Map["print-all-options"]->setHiddenFlag(cl::NotHidden); 1295 Map["print-all-options"]->setCategory(AnotherCategory); 1296 1297 //Hide an option we don't want to see 1298 assert(Map.count("enable-no-infs-fp-math") > 0); 1299 Map["enable-no-infs-fp-math"]->setHiddenFlag(cl::Hidden); 1300 1301 //Change --version to --show-version 1302 assert(Map.count("version") > 0); 1303 Map["version"]->setArgStr("show-version"); 1304 1305 //Change --help description 1306 assert(Map.count("help") > 0); 1307 Map["help"]->setDescription("Shows help"); 1308 1309 cl::ParseCommandLineOptions(argc, argv, "This is a small program to demo the LLVM CommandLine API"); 1310 ... 1311 } 1312 1313 1314.. _cl::ParseCommandLineOptions: 1315 1316The ``cl::ParseCommandLineOptions`` function 1317^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1318 1319The ``cl::ParseCommandLineOptions`` function is designed to be called directly 1320from ``main``, and is used to fill in the values of all of the command line 1321option variables once ``argc`` and ``argv`` are available. 1322 1323The ``cl::ParseCommandLineOptions`` function requires two parameters (``argc`` 1324and ``argv``), but may also take an optional third parameter which holds 1325`additional extra text`_ to emit when the ``-help`` option is invoked. 1326 1327.. _cl::ParseEnvironmentOptions: 1328 1329The ``cl::ParseEnvironmentOptions`` function 1330^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1331 1332The ``cl::ParseEnvironmentOptions`` function has mostly the same effects as 1333`cl::ParseCommandLineOptions`_, except that it is designed to take values for 1334options from an environment variable, for those cases in which reading the 1335command line is not convenient or desired. It fills in the values of all the 1336command line option variables just like `cl::ParseCommandLineOptions`_ does. 1337 1338It takes four parameters: the name of the program (since ``argv`` may not be 1339available, it can't just look in ``argv[0]``), the name of the environment 1340variable to examine, and the optional `additional extra text`_ to emit when the 1341``-help`` option is invoked. 1342 1343``cl::ParseEnvironmentOptions`` will break the environment variable's value up 1344into words and then process them using `cl::ParseCommandLineOptions`_. 1345**Note:** Currently ``cl::ParseEnvironmentOptions`` does not support quoting, so 1346an environment variable containing ``-option "foo bar"`` will be parsed as three 1347words, ``-option``, ``"foo``, and ``bar"``, which is different from what you 1348would get from the shell with the same input. 1349 1350The ``cl::SetVersionPrinter`` function 1351^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1352 1353The ``cl::SetVersionPrinter`` function is designed to be called directly from 1354``main`` and *before* ``cl::ParseCommandLineOptions``. Its use is optional. It 1355simply arranges for a function to be called in response to the ``--version`` 1356option instead of having the ``CommandLine`` library print out the usual version 1357string for LLVM. This is useful for programs that are not part of LLVM but wish 1358to use the ``CommandLine`` facilities. Such programs should just define a small 1359function that takes no arguments and returns ``void`` and that prints out 1360whatever version information is appropriate for the program. Pass the address of 1361that function to ``cl::SetVersionPrinter`` to arrange for it to be called when 1362the ``--version`` option is given by the user. 1363 1364.. _cl::opt: 1365.. _scalar: 1366 1367The ``cl::opt`` class 1368^^^^^^^^^^^^^^^^^^^^^ 1369 1370The ``cl::opt`` class is the class used to represent scalar command line 1371options, and is the one used most of the time. It is a templated class which 1372can take up to three arguments (all except for the first have default values 1373though): 1374 1375.. code-block:: c++ 1376 1377 namespace cl { 1378 template <class DataType, bool ExternalStorage = false, 1379 class ParserClass = parser<DataType> > 1380 class opt; 1381 } 1382 1383The first template argument specifies what underlying data type the command line 1384argument is, and is used to select a default parser implementation. The second 1385template argument is used to specify whether the option should contain the 1386storage for the option (the default) or whether external storage should be used 1387to contain the value parsed for the option (see `Internal vs External Storage`_ 1388for more information). 1389 1390The third template argument specifies which parser to use. The default value 1391selects an instantiation of the ``parser`` class based on the underlying data 1392type of the option. In general, this default works well for most applications, 1393so this option is only used when using a `custom parser`_. 1394 1395.. _lists of arguments: 1396.. _cl::list: 1397 1398The ``cl::list`` class 1399^^^^^^^^^^^^^^^^^^^^^^ 1400 1401The ``cl::list`` class is the class used to represent a list of command line 1402options. It too is a templated class which can take up to three arguments: 1403 1404.. code-block:: c++ 1405 1406 namespace cl { 1407 template <class DataType, class Storage = bool, 1408 class ParserClass = parser<DataType> > 1409 class list; 1410 } 1411 1412This class works the exact same as the `cl::opt`_ class, except that the second 1413argument is the **type** of the external storage, not a boolean value. For this 1414class, the marker type '``bool``' is used to indicate that internal storage 1415should be used. 1416 1417.. _cl::bits: 1418 1419The ``cl::bits`` class 1420^^^^^^^^^^^^^^^^^^^^^^ 1421 1422The ``cl::bits`` class is the class used to represent a list of command line 1423options in the form of a bit vector. It is also a templated class which can 1424take up to three arguments: 1425 1426.. code-block:: c++ 1427 1428 namespace cl { 1429 template <class DataType, class Storage = bool, 1430 class ParserClass = parser<DataType> > 1431 class bits; 1432 } 1433 1434This class works the exact same as the `cl::list`_ class, except that the second 1435argument must be of **type** ``unsigned`` if external storage is used. 1436 1437.. _cl::alias: 1438 1439The ``cl::alias`` class 1440^^^^^^^^^^^^^^^^^^^^^^^ 1441 1442The ``cl::alias`` class is a nontemplated class that is used to form aliases for 1443other arguments. 1444 1445.. code-block:: c++ 1446 1447 namespace cl { 1448 class alias; 1449 } 1450 1451The `cl::aliasopt`_ attribute should be used to specify which option this is an 1452alias for. Alias arguments default to being `cl::Hidden`_, and use the aliased 1453options parser to do the conversion from string to data. 1454 1455.. _cl::extrahelp: 1456 1457The ``cl::extrahelp`` class 1458^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1459 1460The ``cl::extrahelp`` class is a nontemplated class that allows extra help text 1461to be printed out for the ``-help`` option. 1462 1463.. code-block:: c++ 1464 1465 namespace cl { 1466 struct extrahelp; 1467 } 1468 1469To use the extrahelp, simply construct one with a ``const char*`` parameter to 1470the constructor. The text passed to the constructor will be printed at the 1471bottom of the help message, verbatim. Note that multiple ``cl::extrahelp`` 1472**can** be used, but this practice is discouraged. If your tool needs to print 1473additional help information, put all that help into a single ``cl::extrahelp`` 1474instance. 1475 1476For example: 1477 1478.. code-block:: c++ 1479 1480 cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); 1481 1482.. _cl::OptionCategory: 1483 1484The ``cl::OptionCategory`` class 1485^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1486 1487The ``cl::OptionCategory`` class is a simple class for declaring 1488option categories. 1489 1490.. code-block:: c++ 1491 1492 namespace cl { 1493 class OptionCategory; 1494 } 1495 1496An option category must have a name and optionally a description which are 1497passed to the constructor as ``const char*``. 1498 1499Note that declaring an option category and associating it with an option before 1500parsing options (e.g. statically) will change the output of ``-help`` from 1501uncategorized to categorized. If an option category is declared but not 1502associated with an option then it will be hidden from the output of ``-help`` 1503but will be shown in the output of ``-help-hidden``. 1504 1505.. _different parser: 1506.. _discussed previously: 1507 1508Builtin parsers 1509--------------- 1510 1511Parsers control how the string value taken from the command line is translated 1512into a typed value, suitable for use in a C++ program. By default, the 1513CommandLine library uses an instance of ``parser<type>`` if the command line 1514option specifies that it uses values of type '``type``'. Because of this, 1515custom option processing is specified with specializations of the '``parser``' 1516class. 1517 1518The CommandLine library provides the following builtin parser specializations, 1519which are sufficient for most applications. It can, however, also be extended to 1520work with new data types and new ways of interpreting the same data. See the 1521`Writing a Custom Parser`_ for more details on this type of library extension. 1522 1523.. _enums: 1524.. _cl::parser: 1525 1526* The generic ``parser<t>`` parser can be used to map strings values to any data 1527 type, through the use of the `cl::values`_ property, which specifies the 1528 mapping information. The most common use of this parser is for parsing enum 1529 values, which allows you to use the CommandLine library for all of the error 1530 checking to make sure that only valid enum values are specified (as opposed to 1531 accepting arbitrary strings). Despite this, however, the generic parser class 1532 can be used for any data type. 1533 1534.. _boolean flags: 1535.. _bool parser: 1536 1537* The **parser<bool> specialization** is used to convert boolean strings to a 1538 boolean value. Currently accepted strings are "``true``", "``TRUE``", 1539 "``True``", "``1``", "``false``", "``FALSE``", "``False``", and "``0``". 1540 1541* The **parser<boolOrDefault> specialization** is used for cases where the value 1542 is boolean, but we also need to know whether the option was specified at all. 1543 boolOrDefault is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. 1544 This parser accepts the same strings as **``parser<bool>``**. 1545 1546.. _strings: 1547 1548* The **parser<string> specialization** simply stores the parsed string into the 1549 string value specified. No conversion or modification of the data is 1550 performed. 1551 1552.. _integers: 1553.. _int: 1554 1555* The **parser<int> specialization** uses the C ``strtol`` function to parse the 1556 string input. As such, it will accept a decimal number (with an optional '+' 1557 or '-' prefix) which must start with a non-zero digit. It accepts octal 1558 numbers, which are identified with a '``0``' prefix digit, and hexadecimal 1559 numbers with a prefix of '``0x``' or '``0X``'. 1560 1561.. _doubles: 1562.. _float: 1563.. _double: 1564 1565* The **parser<double>** and **parser<float> specializations** use the standard 1566 C ``strtod`` function to convert floating point strings into floating point 1567 values. As such, a broad range of string formats is supported, including 1568 exponential notation (ex: ``1.7e15``) and properly supports locales. 1569 1570.. _Extension Guide: 1571.. _extending the library: 1572 1573Extension Guide 1574=============== 1575 1576Although the CommandLine library has a lot of functionality built into it 1577already (as discussed previously), one of its true strengths lie in its 1578extensibility. This section discusses how the CommandLine library works under 1579the covers and illustrates how to do some simple, common, extensions. 1580 1581.. _Custom parsers: 1582.. _custom parser: 1583.. _Writing a Custom Parser: 1584 1585Writing a custom parser 1586----------------------- 1587 1588One of the simplest and most common extensions is the use of a custom parser. 1589As `discussed previously`_, parsers are the portion of the CommandLine library 1590that turns string input from the user into a particular parsed data type, 1591validating the input in the process. 1592 1593There are two ways to use a new parser: 1594 1595#. Specialize the `cl::parser`_ template for your custom data type. 1596 1597 This approach has the advantage that users of your custom data type will 1598 automatically use your custom parser whenever they define an option with a 1599 value type of your data type. The disadvantage of this approach is that it 1600 doesn't work if your fundamental data type is something that is already 1601 supported. 1602 1603#. Write an independent class, using it explicitly from options that need it. 1604 1605 This approach works well in situations where you would line to parse an 1606 option using special syntax for a not-very-special data-type. The drawback 1607 of this approach is that users of your parser have to be aware that they are 1608 using your parser instead of the builtin ones. 1609 1610To guide the discussion, we will discuss a custom parser that accepts file 1611sizes, specified with an optional unit after the numeric size. For example, we 1612would like to parse "102kb", "41M", "1G" into the appropriate integer value. In 1613this case, the underlying data type we want to parse into is '``unsigned``'. We 1614choose approach #2 above because we don't want to make this the default for all 1615``unsigned`` options. 1616 1617To start out, we declare our new ``FileSizeParser`` class: 1618 1619.. code-block:: c++ 1620 1621 struct FileSizeParser : public cl::parser<unsigned> { 1622 // parse - Return true on error. 1623 bool parse(cl::Option &O, StringRef ArgName, const std::string &ArgValue, 1624 unsigned &Val); 1625 }; 1626 1627Our new class inherits from the ``cl::parser`` template class to fill in 1628the default, boiler plate code for us. We give it the data type that we parse 1629into, the last argument to the ``parse`` method, so that clients of our custom 1630parser know what object type to pass in to the parse method. (Here we declare 1631that we parse into '``unsigned``' variables.) 1632 1633For most purposes, the only method that must be implemented in a custom parser 1634is the ``parse`` method. The ``parse`` method is called whenever the option is 1635invoked, passing in the option itself, the option name, the string to parse, and 1636a reference to a return value. If the string to parse is not well-formed, the 1637parser should output an error message and return true. Otherwise it should 1638return false and set '``Val``' to the parsed value. In our example, we 1639implement ``parse`` as: 1640 1641.. code-block:: c++ 1642 1643 bool FileSizeParser::parse(cl::Option &O, StringRef ArgName, 1644 const std::string &Arg, unsigned &Val) { 1645 const char *ArgStart = Arg.c_str(); 1646 char *End; 1647 1648 // Parse integer part, leaving 'End' pointing to the first non-integer char 1649 Val = (unsigned)strtol(ArgStart, &End, 0); 1650 1651 while (1) { 1652 switch (*End++) { 1653 case 0: return false; // No error 1654 case 'i': // Ignore the 'i' in KiB if people use that 1655 case 'b': case 'B': // Ignore B suffix 1656 break; 1657 1658 case 'g': case 'G': Val *= 1024*1024*1024; break; 1659 case 'm': case 'M': Val *= 1024*1024; break; 1660 case 'k': case 'K': Val *= 1024; break; 1661 1662 default: 1663 // Print an error message if unrecognized character! 1664 return O.error("'" + Arg + "' value invalid for file size argument!"); 1665 } 1666 } 1667 } 1668 1669This function implements a very simple parser for the kinds of strings we are 1670interested in. Although it has some holes (it allows "``123KKK``" for example), 1671it is good enough for this example. Note that we use the option itself to print 1672out the error message (the ``error`` method always returns true) in order to get 1673a nice error message (shown below). Now that we have our parser class, we can 1674use it like this: 1675 1676.. code-block:: c++ 1677 1678 static cl::opt<unsigned, false, FileSizeParser> 1679 MFS("max-file-size", cl::desc("Maximum file size to accept"), 1680 cl::value_desc("size")); 1681 1682Which adds this to the output of our program: 1683 1684:: 1685 1686 OPTIONS: 1687 -help - display available options (-help-hidden for more) 1688 ... 1689 -max-file-size=<size> - Maximum file size to accept 1690 1691And we can test that our parse works correctly now (the test program just prints 1692out the max-file-size argument value): 1693 1694:: 1695 1696 $ ./test 1697 MFS: 0 1698 $ ./test -max-file-size=123MB 1699 MFS: 128974848 1700 $ ./test -max-file-size=3G 1701 MFS: 3221225472 1702 $ ./test -max-file-size=dog 1703 -max-file-size option: 'dog' value invalid for file size argument! 1704 1705It looks like it works. The error message that we get is nice and helpful, and 1706we seem to accept reasonable file sizes. This wraps up the "custom parser" 1707tutorial. 1708 1709Exploiting external storage 1710--------------------------- 1711 1712Several of the LLVM libraries define static ``cl::opt`` instances that will 1713automatically be included in any program that links with that library. This is 1714a feature. However, sometimes it is necessary to know the value of the command 1715line option outside of the library. In these cases the library does or should 1716provide an external storage location that is accessible to users of the 1717library. Examples of this include the ``llvm::DebugFlag`` exported by the 1718``lib/Support/Debug.cpp`` file and the ``llvm::TimePassesIsEnabled`` flag 1719exported by the ``lib/IR/PassManager.cpp`` file. 1720 1721.. todo:: 1722 1723 TODO: complete this section 1724 1725.. _dynamically loaded options: 1726 1727Dynamically adding command line options 1728--------------------------------------- 1729 1730.. todo:: 1731 1732 TODO: fill in this section 1733