| ============================== |
| CommandLine 2.0 Library Manual |
| ============================== |
| |
| .. contents:: |
| :local: |
| |
| Introduction |
| ============ |
| |
| This document describes the CommandLine argument processing library. It will |
| show you how to use it, and what it can do. The CommandLine library uses a |
| declarative approach to specifying the command line options that your program |
| takes. By default, these options declarations implicitly hold the value parsed |
| for the option declared (of course this `can be changed`_). |
| |
| Although there are a **lot** of command line argument parsing libraries out |
| there in many different languages, none of them fit well with what I needed. By |
| looking at the features and problems of other libraries, I designed the |
| CommandLine library to have the following features: |
| |
| #. Speed: The CommandLine library is very quick and uses little resources. The |
| parsing time of the library is directly proportional to the number of |
| arguments parsed, not the number of options recognized. Additionally, |
| command line argument values are captured transparently into user defined |
| global variables, which can be accessed like any other variable (and with the |
| same performance). |
| |
| #. Type Safe: As a user of CommandLine, you don't have to worry about |
| remembering the type of arguments that you want (is it an int? a string? a |
| bool? an enum?) and keep casting it around. Not only does this help prevent |
| error prone constructs, it also leads to dramatically cleaner source code. |
| |
| #. No subclasses required: To use CommandLine, you instantiate variables that |
| correspond to the arguments that you would like to capture, you don't |
| subclass a parser. This means that you don't have to write **any** |
| boilerplate code. |
| |
| #. Globally accessible: Libraries can specify command line arguments that are |
| automatically enabled in any tool that links to the library. This is |
| possible because the application doesn't have to keep a list of arguments to |
| pass to the parser. This also makes supporting `dynamically loaded options`_ |
| trivial. |
| |
| #. Cleaner: CommandLine supports enum and other types directly, meaning that |
| there is less error and more security built into the library. You don't have |
| to worry about whether your integral command line argument accidentally got |
| assigned a value that is not valid for your enum type. |
| |
| #. Powerful: The CommandLine library supports many different types of arguments, |
| from simple `boolean flags`_ to `scalars arguments`_ (`strings`_, |
| `integers`_, `enums`_, `doubles`_), to `lists of arguments`_. This is |
| possible because CommandLine is... |
| |
| #. Extensible: It is very simple to add a new argument type to CommandLine. |
| Simply specify the parser that you want to use with the command line option |
| when you declare it. `Custom parsers`_ are no problem. |
| |
| #. Labor Saving: The CommandLine library cuts down on the amount of grunt work |
| that you, the user, have to do. For example, it automatically provides a |
| ``-help`` option that shows the available command line options for your tool. |
| Additionally, it does most of the basic correctness checking for you. |
| |
| #. Capable: The CommandLine library can handle lots of different forms of |
| options often found in real programs. For example, `positional`_ arguments, |
| ``ls`` style `grouping`_ options (to allow processing '``ls -lad``' |
| naturally), ``ld`` style `prefix`_ options (to parse '``-lmalloc |
| -L/usr/lib``'), and interpreter style options. |
| |
| This document will hopefully let you jump in and start using CommandLine in your |
| utility quickly and painlessly. Additionally it should be a simple reference |
| manual to figure out how stuff works. |
| |
| Quick Start Guide |
| ================= |
| |
| This section of the manual runs through a simple CommandLine'ification of a |
| basic compiler tool. This is intended to show you how to jump into using the |
| CommandLine library in your own program, and show you some of the cool things it |
| can do. |
| |
| To start out, you need to include the CommandLine header file into your program: |
| |
| .. code-block:: c++ |
| |
| #include "llvm/Support/CommandLine.h" |
| |
| Additionally, you need to add this as the first line of your main program: |
| |
| .. code-block:: c++ |
| |
| int main(int argc, char **argv) { |
| cl::ParseCommandLineOptions(argc, argv); |
| ... |
| } |
| |
| ... which actually parses the arguments and fills in the variable declarations. |
| |
| Now that you are ready to support command line arguments, we need to tell the |
| system which ones we want, and what type of arguments they are. The CommandLine |
| library uses a declarative syntax to model command line arguments with the |
| global variable declarations that capture the parsed values. This means that |
| for every command line option that you would like to support, there should be a |
| global variable declaration to capture the result. For example, in a compiler, |
| we would like to support the Unix-standard '``-o <filename>``' option to specify |
| where to put the output. With the CommandLine library, this is represented like |
| this: |
| |
| .. _scalars arguments: |
| .. _here: |
| |
| .. code-block:: c++ |
| |
| cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename")); |
| |
| This declares a global variable "``OutputFilename``" that is used to capture the |
| result of the "``o``" argument (first parameter). We specify that this is a |
| simple scalar option by using the "``cl::opt``" template (as opposed to the |
| "``cl::list``" template), and tell the CommandLine library that the data |
| type that we are parsing is a string. |
| |
| The second and third parameters (which are optional) are used to specify what to |
| output for the "``-help``" option. In this case, we get a line that looks like |
| this: |
| |
| :: |
| |
| USAGE: compiler [options] |
| |
| OPTIONS: |
| -h - Alias for -help |
| -help - display available options (-help-hidden for more) |
| -o <filename> - Specify output filename |
| |
| Because we specified that the command line option should parse using the |
| ``string`` data type, the variable declared is automatically usable as a real |
| string in all contexts that a normal C++ string object may be used. For |
| example: |
| |
| .. code-block:: c++ |
| |
| ... |
| std::ofstream Output(OutputFilename.c_str()); |
| if (Output.good()) ... |
| ... |
| |
| There are many different options that you can use to customize the command line |
| option handling library, but the above example shows the general interface to |
| these options. The options can be specified in any order, and are specified |
| with helper functions like `cl::desc(...)`_, so there are no positional |
| dependencies to remember. The available options are discussed in detail in the |
| `Reference Guide`_. |
| |
| Continuing the example, we would like to have our compiler take an input |
| filename as well as an output filename, but we do not want the input filename to |
| be specified with a hyphen (ie, not ``-filename.c``). To support this style of |
| argument, the CommandLine library allows for `positional`_ arguments to be |
| specified for the program. These positional arguments are filled with command |
| line parameters that are not in option form. We use this feature like this: |
| |
| .. code-block:: c++ |
| |
| |
| cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-")); |
| |
| This declaration indicates that the first positional argument should be treated |
| as the input filename. Here we use the `cl::init`_ option to specify an initial |
| value for the command line option, which is used if the option is not specified |
| (if you do not specify a `cl::init`_ modifier for an option, then the default |
| constructor for the data type is used to initialize the value). Command line |
| options default to being optional, so if we would like to require that the user |
| always specify an input filename, we would add the `cl::Required`_ flag, and we |
| could eliminate the `cl::init`_ modifier, like this: |
| |
| .. code-block:: c++ |
| |
| cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::Required); |
| |
| Again, the CommandLine library does not require the options to be specified in |
| any particular order, so the above declaration is equivalent to: |
| |
| .. code-block:: c++ |
| |
| cl::opt<string> InputFilename(cl::Positional, cl::Required, cl::desc("<input file>")); |
| |
| By simply adding the `cl::Required`_ flag, the CommandLine library will |
| automatically issue an error if the argument is not specified, which shifts all |
| of the command line option verification code out of your application into the |
| library. This is just one example of how using flags can alter the default |
| behaviour of the library, on a per-option basis. By adding one of the |
| declarations above, the ``-help`` option synopsis is now extended to: |
| |
| :: |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| -h - Alias for -help |
| -help - display available options (-help-hidden for more) |
| -o <filename> - Specify output filename |
| |
| ... indicating that an input filename is expected. |
| |
| Boolean Arguments |
| ----------------- |
| |
| In addition to input and output filenames, we would like the compiler example to |
| support three boolean flags: "``-f``" to force writing binary output to a |
| terminal, "``--quiet``" to enable quiet mode, and "``-q``" for backwards |
| compatibility with some of our users. We can support these by declaring options |
| of boolean type like this: |
| |
| .. code-block:: c++ |
| |
| cl::opt<bool> Force ("f", cl::desc("Enable binary output on terminals")); |
| cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); |
| cl::opt<bool> Quiet2("q", cl::desc("Don't print informational messages"), cl::Hidden); |
| |
| This does what you would expect: it declares three boolean variables |
| ("``Force``", "``Quiet``", and "``Quiet2``") to recognize these options. Note |
| that the "``-q``" option is specified with the "`cl::Hidden`_" flag. This |
| modifier prevents it from being shown by the standard "``-help``" output (note |
| that it is still shown in the "``-help-hidden``" output). |
| |
| The CommandLine library uses a `different parser`_ for different data types. |
| For example, in the string case, the argument passed to the option is copied |
| literally into the content of the string variable... we obviously cannot do that |
| in the boolean case, however, so we must use a smarter parser. In the case of |
| the boolean parser, it allows no options (in which case it assigns the value of |
| true to the variable), or it allows the values "``true``" or "``false``" to be |
| specified, allowing any of the following inputs: |
| |
| :: |
| |
| compiler -f # No value, 'Force' == true |
| compiler -f=true # Value specified, 'Force' == true |
| compiler -f=TRUE # Value specified, 'Force' == true |
| compiler -f=FALSE # Value specified, 'Force' == false |
| |
| ... you get the idea. The `bool parser`_ just turns the string values into |
| boolean values, and rejects things like '``compiler -f=foo``'. Similarly, the |
| `float`_, `double`_, and `int`_ parsers work like you would expect, using the |
| '``strtol``' and '``strtod``' C library calls to parse the string value into the |
| specified data type. |
| |
| With the declarations above, "``compiler -help``" emits this: |
| |
| :: |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| -f - Enable binary output on terminals |
| -o - Override output filename |
| -quiet - Don't print informational messages |
| -help - display available options (-help-hidden for more) |
| |
| and "``compiler -help-hidden``" prints this: |
| |
| :: |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| -f - Enable binary output on terminals |
| -o - Override output filename |
| -q - Don't print informational messages |
| -quiet - Don't print informational messages |
| -help - display available options (-help-hidden for more) |
| |
| This brief example has shown you how to use the '`cl::opt`_' class to parse |
| simple scalar command line arguments. In addition to simple scalar arguments, |
| the CommandLine library also provides primitives to support CommandLine option |
| `aliases`_, and `lists`_ of options. |
| |
| .. _aliases: |
| |
| Argument Aliases |
| ---------------- |
| |
| So far, the example works well, except for the fact that we need to check the |
| quiet condition like this now: |
| |
| .. code-block:: c++ |
| |
| ... |
| if (!Quiet && !Quiet2) printInformationalMessage(...); |
| ... |
| |
| ... which is a real pain! Instead of defining two values for the same |
| condition, we can use the "`cl::alias`_" class to make the "``-q``" option an |
| **alias** for the "``-quiet``" option, instead of providing a value itself: |
| |
| .. code-block:: c++ |
| |
| cl::opt<bool> Force ("f", cl::desc("Overwrite output files")); |
| cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); |
| cl::alias QuietA("q", cl::desc("Alias for -quiet"), cl::aliasopt(Quiet)); |
| |
| The third line (which is the only one we modified from above) defines a "``-q``" |
| alias that updates the "``Quiet``" variable (as specified by the `cl::aliasopt`_ |
| modifier) whenever it is specified. Because aliases do not hold state, the only |
| thing the program has to query is the ``Quiet`` variable now. Another nice |
| feature of aliases is that they automatically hide themselves from the ``-help`` |
| output (although, again, they are still visible in the ``-help-hidden output``). |
| |
| Now the application code can simply use: |
| |
| .. code-block:: c++ |
| |
| ... |
| if (!Quiet) printInformationalMessage(...); |
| ... |
| |
| ... which is much nicer! The "`cl::alias`_" can be used to specify an |
| alternative name for any variable type, and has many uses. |
| |
| .. _unnamed alternatives using the generic parser: |
| |
| Selecting an alternative from a set of possibilities |
| ---------------------------------------------------- |
| |
| So far we have seen how the CommandLine library handles builtin types like |
| ``std::string``, ``bool`` and ``int``, but how does it handle things it doesn't |
| know about, like enums or '``int*``'s? |
| |
| The answer is that it uses a table-driven generic parser (unless you specify |
| your own parser, as described in the `Extension Guide`_). This parser maps |
| literal strings to whatever type is required, and requires you to tell it what |
| this mapping should be. |
| |
| Let's say that we would like to add four optimization levels to our optimizer, |
| using the standard flags "``-g``", "``-O0``", "``-O1``", and "``-O2``". We |
| could easily implement this with boolean options like above, but there are |
| several problems with this strategy: |
| |
| #. A user could specify more than one of the options at a time, for example, |
| "``compiler -O3 -O2``". The CommandLine library would not be able to catch |
| this erroneous input for us. |
| |
| #. We would have to test 4 different variables to see which ones are set. |
| |
| #. This doesn't map to the numeric levels that we want... so we cannot easily |
| see if some level >= "``-O1``" is enabled. |
| |
| To cope with these problems, we can use an enum value, and have the CommandLine |
| library fill it in with the appropriate level directly, which is used like this: |
| |
| .. code-block:: c++ |
| |
| enum OptLevel { |
| g, O1, O2, O3 |
| }; |
| |
| cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"), |
| cl::values( |
| clEnumVal(g , "No optimizations, enable debugging"), |
| clEnumVal(O1, "Enable trivial optimizations"), |
| clEnumVal(O2, "Enable default optimizations"), |
| clEnumVal(O3, "Enable expensive optimizations"))); |
| |
| ... |
| if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); |
| ... |
| |
| This declaration defines a variable "``OptimizationLevel``" of the |
| "``OptLevel``" enum type. This variable can be assigned any of the values that |
| are listed in the declaration. The CommandLine library enforces that |
| the user can only specify one of the options, and it ensure that only valid enum |
| values can be specified. The "``clEnumVal``" macros ensure that the command |
| line arguments matched the enum values. With this option added, our help output |
| now is: |
| |
| :: |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| Choose optimization level: |
| -g - No optimizations, enable debugging |
| -O1 - Enable trivial optimizations |
| -O2 - Enable default optimizations |
| -O3 - Enable expensive optimizations |
| -f - Enable binary output on terminals |
| -help - display available options (-help-hidden for more) |
| -o <filename> - Specify output filename |
| -quiet - Don't print informational messages |
| |
| In this case, it is sort of awkward that flag names correspond directly to enum |
| names, because we probably don't want an enum definition named "``g``" in our |
| program. Because of this, we can alternatively write this example like this: |
| |
| .. code-block:: c++ |
| |
| enum OptLevel { |
| Debug, O1, O2, O3 |
| }; |
| |
| cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"), |
| cl::values( |
| clEnumValN(Debug, "g", "No optimizations, enable debugging"), |
| clEnumVal(O1 , "Enable trivial optimizations"), |
| clEnumVal(O2 , "Enable default optimizations"), |
| clEnumVal(O3 , "Enable expensive optimizations"))); |
| |
| ... |
| if (OptimizationLevel == Debug) outputDebugInfo(...); |
| ... |
| |
| By using the "``clEnumValN``" macro instead of "``clEnumVal``", we can directly |
| specify the name that the flag should get. In general a direct mapping is nice, |
| but sometimes you can't or don't want to preserve the mapping, which is when you |
| would use it. |
| |
| Named Alternatives |
| ------------------ |
| |
| Another useful argument form is a named alternative style. We shall use this |
| style in our compiler to specify different debug levels that can be used. |
| Instead of each debug level being its own switch, we want to support the |
| following options, of which only one can be specified at a time: |
| "``--debug-level=none``", "``--debug-level=quick``", |
| "``--debug-level=detailed``". To do this, we use the exact same format as our |
| optimization level flags, but we also specify an option name. For this case, |
| the code looks like this: |
| |
| .. code-block:: c++ |
| |
| enum DebugLev { |
| nodebuginfo, quick, detailed |
| }; |
| |
| // Enable Debug Options to be specified on the command line |
| cl::opt<DebugLev> DebugLevel("debug_level", cl::desc("Set the debugging level:"), |
| cl::values( |
| clEnumValN(nodebuginfo, "none", "disable debug information"), |
| clEnumVal(quick, "enable quick debug information"), |
| clEnumVal(detailed, "enable detailed debug information"))); |
| |
| This definition defines an enumerated command line variable of type "``enum |
| DebugLev``", which works exactly the same way as before. The difference here is |
| just the interface exposed to the user of your program and the help output by |
| the "``-help``" option: |
| |
| :: |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| Choose optimization level: |
| -g - No optimizations, enable debugging |
| -O1 - Enable trivial optimizations |
| -O2 - Enable default optimizations |
| -O3 - Enable expensive optimizations |
| -debug_level - Set the debugging level: |
| =none - disable debug information |
| =quick - enable quick debug information |
| =detailed - enable detailed debug information |
| -f - Enable binary output on terminals |
| -help - display available options (-help-hidden for more) |
| -o <filename> - Specify output filename |
| -quiet - Don't print informational messages |
| |
| Again, the only structural difference between the debug level declaration and |
| the optimization level declaration is that the debug level declaration includes |
| an option name (``"debug_level"``), which automatically changes how the library |
| processes the argument. The CommandLine library supports both forms so that you |
| can choose the form most appropriate for your application. |
| |
| .. _lists: |
| |
| Parsing a list of options |
| ------------------------- |
| |
| Now that we have the standard run-of-the-mill argument types out of the way, |
| lets get a little wild and crazy. Lets say that we want our optimizer to accept |
| a **list** of optimizations to perform, allowing duplicates. For example, we |
| might want to run: "``compiler -dce -instsimplify -inline -dce -strip``". In this |
| case, the order of the arguments and the number of appearances is very |
| important. This is what the "``cl::list``" template is for. First, start by |
| defining an enum of the optimizations that you would like to perform: |
| |
| .. code-block:: c++ |
| |
| enum Opts { |
| // 'inline' is a C++ keyword, so name it 'inlining' |
| dce, instsimplify, inlining, strip |
| }; |
| |
| Then define your "``cl::list``" variable: |
| |
| .. code-block:: c++ |
| |
| cl::list<Opts> OptimizationList(cl::desc("Available Optimizations:"), |
| cl::values( |
| clEnumVal(dce , "Dead Code Elimination"), |
| clEnumVal(instsimplify , "Instruction Simplification"), |
| clEnumValN(inlining, "inline", "Procedure Integration"), |
| clEnumVal(strip , "Strip Symbols"))); |
| |
| This defines a variable that is conceptually of the type |
| "``std::vector<enum Opts>``". Thus, you can access it with standard vector |
| methods: |
| |
| .. code-block:: c++ |
| |
| for (unsigned i = 0; i != OptimizationList.size(); ++i) |
| switch (OptimizationList[i]) |
| ... |
| |
| ... to iterate through the list of options specified. |
| |
| Note that the "``cl::list``" template is completely general and may be used with |
| any data types or other arguments that you can use with the "``cl::opt``" |
| template. One especially useful way to use a list is to capture all of the |
| positional arguments together if there may be more than one specified. In the |
| case of a linker, for example, the linker takes several '``.o``' files, and |
| needs to capture them into a list. This is naturally specified as: |
| |
| .. code-block:: c++ |
| |
| ... |
| cl::list<std::string> InputFilenames(cl::Positional, cl::desc("<Input files>"), cl::OneOrMore); |
| ... |
| |
| This variable works just like a "``vector<string>``" object. As such, accessing |
| the list is simple, just like above. In this example, we used the |
| `cl::OneOrMore`_ modifier to inform the CommandLine library that it is an error |
| if the user does not specify any ``.o`` files on our command line. Again, this |
| just reduces the amount of checking we have to do. |
| |
| Collecting options as a set of flags |
| ------------------------------------ |
| |
| Instead of collecting sets of options in a list, it is also possible to gather |
| information for enum values in a **bit vector**. The representation used by the |
| `cl::bits`_ class is an ``unsigned`` integer. An enum value is represented by a |
| 0/1 in the enum's ordinal value bit position. 1 indicating that the enum was |
| specified, 0 otherwise. As each specified value is parsed, the resulting enum's |
| bit is set in the option's bit vector: |
| |
| .. code-block:: c++ |
| |
| bits |= 1 << (unsigned)enum; |
| |
| Options that are specified multiple times are redundant. Any instances after |
| the first are discarded. |
| |
| Reworking the above list example, we could replace `cl::list`_ with `cl::bits`_: |
| |
| .. code-block:: c++ |
| |
| cl::bits<Opts> OptimizationBits(cl::desc("Available Optimizations:"), |
| cl::values( |
| clEnumVal(dce , "Dead Code Elimination"), |
| clEnumVal(instsimplify , "Instruction Simplification"), |
| clEnumValN(inlining, "inline", "Procedure Integration"), |
| clEnumVal(strip , "Strip Symbols"))); |
| |
| To test to see if ``instsimplify`` was specified, we can use the ``cl:bits::isSet`` |
| function: |
| |
| .. code-block:: c++ |
| |
| if (OptimizationBits.isSet(instsimplify)) { |
| ... |
| } |
| |
| It's also possible to get the raw bit vector using the ``cl::bits::getBits`` |
| function: |
| |
| .. code-block:: c++ |
| |
| unsigned bits = OptimizationBits.getBits(); |
| |
| Finally, if external storage is used, then the location specified must be of |
| **type** ``unsigned``. In all other ways a `cl::bits`_ option is equivalent to a |
| `cl::list`_ option. |
| |
| .. _additional extra text: |
| |
| Adding freeform text to help output |
| ----------------------------------- |
| |
| As our program grows and becomes more mature, we may decide to put summary |
| information about what it does into the help output. The help output is styled |
| to look similar to a Unix ``man`` page, providing concise information about a |
| program. Unix ``man`` pages, however often have a description about what the |
| program does. To add this to your CommandLine program, simply pass a third |
| argument to the `cl::ParseCommandLineOptions`_ call in main. This additional |
| argument is then printed as the overview information for your program, allowing |
| you to include any additional information that you want. For example: |
| |
| .. code-block:: c++ |
| |
| int main(int argc, char **argv) { |
| cl::ParseCommandLineOptions(argc, argv, " CommandLine compiler example\n\n" |
| " This program blah blah blah...\n"); |
| ... |
| } |
| |
| would yield the help output: |
| |
| :: |
| |
| **OVERVIEW: CommandLine compiler example |
| |
| This program blah blah blah...** |
| |
| USAGE: compiler [options] <input file> |
| |
| OPTIONS: |
| ... |
| -help - display available options (-help-hidden for more) |
| -o <filename> - Specify output filename |
| |
| .. _grouping options into categories: |
| |
| Grouping options into categories |
| -------------------------------- |
| |
| If our program has a large number of options it may become difficult for users |
| of our tool to navigate the output of ``-help``. To alleviate this problem we |
| can put our options into categories. This can be done by declaring option |
| categories (`cl::OptionCategory`_ objects) and then placing our options into |
| these categories using the `cl::cat`_ option attribute. For example: |
| |
| .. code-block:: c++ |
| |
| cl::OptionCategory StageSelectionCat("Stage Selection Options", |
| "These control which stages are run."); |
| |
| cl::opt<bool> Preprocessor("E",cl::desc("Run preprocessor stage."), |
| cl::cat(StageSelectionCat)); |
| |
| cl::opt<bool> NoLink("c",cl::desc("Run all stages except linking."), |
| cl::cat(StageSelectionCat)); |
| |
| The output of ``-help`` will become categorized if an option category is |
| declared. The output looks something like :: |
| |
| OVERVIEW: This is a small program to demo the LLVM CommandLine API |
| USAGE: Sample [options] |
| |
| OPTIONS: |
| |
| General options: |
| |
| -help - Display available options (-help-hidden for more) |
| -help-list - Display list of available options (-help-list-hidden for more) |
| |
| |
| Stage Selection Options: |
| These control which stages are run. |
| |
| -E - Run preprocessor stage. |
| -c - Run all stages except linking. |
| |
| In addition to the behaviour of ``-help`` changing when an option category is |
| declared, the command line option ``-help-list`` becomes visible which will |
| print the command line options as uncategorized list. |
| |
| Note that Options that are not explicitly categorized will be placed in the |
| ``cl::getGeneralCategory()`` category. |
| |
| .. _Reference Guide: |
| |
| Reference Guide |
| =============== |
| |
| Now that you know the basics of how to use the CommandLine library, this section |
| will give you the detailed information you need to tune how command line options |
| work, as well as information on more "advanced" command line option processing |
| capabilities. |
| |
| .. _positional: |
| .. _positional argument: |
| .. _Positional Arguments: |
| .. _Positional arguments section: |
| .. _positional options: |
| |
| Positional Arguments |
| -------------------- |
| |
| Positional arguments are those arguments that are not named, and are not |
| specified with a hyphen. Positional arguments should be used when an option is |
| specified by its position alone. For example, the standard Unix ``grep`` tool |
| takes a regular expression argument, and an optional filename to search through |
| (which defaults to standard input if a filename is not specified). Using the |
| CommandLine library, this would be specified as: |
| |
| .. code-block:: c++ |
| |
| cl::opt<string> Regex (cl::Positional, cl::desc("<regular expression>"), cl::Required); |
| cl::opt<string> Filename(cl::Positional, cl::desc("<input file>"), cl::init("-")); |
| |
| Given these two option declarations, the ``-help`` output for our grep |
| replacement would look like this: |
| |
| :: |
| |
| USAGE: spiffygrep [options] <regular expression> <input file> |
| |
| OPTIONS: |
| -help - display available options (-help-hidden for more) |
| |
| ... and the resultant program could be used just like the standard ``grep`` |
| tool. |
| |
| Positional arguments are sorted by their order of construction. This means that |
| command line options will be ordered according to how they are listed in a .cpp |
| file, but will not have an ordering defined if the positional arguments are |
| defined in multiple .cpp files. The fix for this problem is simply to define |
| all of your positional arguments in one .cpp file. |
| |
| Specifying positional options with hyphens |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| Sometimes you may want to specify a value to your positional argument that |
| starts with a hyphen (for example, searching for '``-foo``' in a file). At |
| first, you will have trouble doing this, because it will try to find an argument |
| named '``-foo``', and will fail (and single quotes will not save you). Note |
| that the system ``grep`` has the same problem: |
| |
| :: |
| |
| $ spiffygrep '-foo' test.txt |
| Unknown command line argument '-foo'. Try: spiffygrep -help' |
| |
| $ grep '-foo' test.txt |
| grep: illegal option -- f |
| grep: illegal option -- o |
| grep: illegal option -- o |
| Usage: grep -hblcnsviw pattern file . . . |
| |
| The solution for this problem is the same for both your tool and the system |
| version: use the '``--``' marker. When the user specifies '``--``' on the |
| command line, it is telling the program that all options after the '``--``' |
| should be treated as positional arguments, not options. Thus, we can use it |
| like this: |
| |
| :: |
| |
| $ spiffygrep -- -foo test.txt |
| ...output... |
| |
| Determining absolute position with getPosition() |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| Sometimes an option can affect or modify the meaning of another option. For |
| example, consider ``gcc``'s ``-x LANG`` option. This tells ``gcc`` to ignore the |
| suffix of subsequent positional arguments and force the file to be interpreted |
| as if it contained source code in language ``LANG``. In order to handle this |
| properly, you need to know the absolute position of each argument, especially |
| those in lists, so their interaction(s) can be applied correctly. This is also |
| useful for options like ``-llibname`` which is actually a positional argument |
| that starts with a dash. |
| |
| So, generally, the problem is that you have two ``cl::list`` variables that |
| interact in some way. To ensure the correct interaction, you can use the |
| ``cl::list::getPosition(optnum)`` method. This method returns the absolute |
| position (as found on the command line) of the ``optnum`` item in the |
| ``cl::list``. |
| |
| The idiom for usage is like this: |
| |
| .. code-block:: c++ |
| |
| static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); |
| static cl::list<std::string> Libraries("l"); |
| |
| int main(int argc, char**argv) { |
| // ... |
| std::vector<std::string>::iterator fileIt = Files.begin(); |
| std::vector<std::string>::iterator libIt = Libraries.begin(); |
| unsigned libPos = 0, filePos = 0; |
| while ( 1 ) { |
| if ( libIt != Libraries.end() ) |
| libPos = Libraries.getPosition( libIt - Libraries.begin() ); |
| else |
| libPos = 0; |
| if ( fileIt != Files.end() ) |
| filePos = Files.getPosition( fileIt - Files.begin() ); |
| else |
| filePos = 0; |
| |
| if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) { |
| // Source File Is next |
| ++fileIt; |
| } |
| else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) { |
| // Library is next |
| ++libIt; |
| } |
| else |
| break; // we're done with the list |
| } |
| } |
| |
| Note that, for compatibility reasons, the ``cl::opt`` also supports an |
| ``unsigned getPosition()`` option that will provide the absolute position of |
| that option. You can apply the same approach as above with a ``cl::opt`` and a |
| ``cl::list`` option as you can with two lists. |
| |
| .. _interpreter style options: |
| .. _cl::ConsumeAfter: |
| .. _this section for more information: |
| |
| The ``cl::ConsumeAfter`` modifier |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::ConsumeAfter`` `formatting option`_ is used to construct programs that |
| use "interpreter style" option processing. With this style of option |
| processing, all arguments specified after the last positional argument are |
| treated as special interpreter arguments that are not interpreted by the command |
| line argument. |
| |
| As a concrete example, lets say we are developing a replacement for the standard |
| Unix Bourne shell (``/bin/sh``). To run ``/bin/sh``, first you specify options |
| to the shell itself (like ``-x`` which turns on trace output), then you specify |
| the name of the script to run, then you specify arguments to the script. These |
| arguments to the script are parsed by the Bourne shell command line option |
| processor, but are not interpreted as options to the shell itself. Using the |
| CommandLine library, we would specify this as: |
| |
| .. code-block:: c++ |
| |
| cl::opt<string> Script(cl::Positional, cl::desc("<input script>"), cl::init("-")); |
| cl::list<string> Argv(cl::ConsumeAfter, cl::desc("<program arguments>...")); |
| cl::opt<bool> Trace("x", cl::desc("Enable trace output")); |
| |
| which automatically provides the help output: |
| |
| :: |
| |
| USAGE: spiffysh [options] <input script> <program arguments>... |
| |
| OPTIONS: |
| -help - display available options (-help-hidden for more) |
| -x - Enable trace output |
| |
| At runtime, if we run our new shell replacement as ```spiffysh -x test.sh -a -x |
| -y bar``', the ``Trace`` variable will be set to true, the ``Script`` variable |
| will be set to "``test.sh``", and the ``Argv`` list will contain ``["-a", "-x", |
| "-y", "bar"]``, because they were specified after the last positional argument |
| (which is the script name). |
| |
| There are several limitations to when ``cl::ConsumeAfter`` options can be |
| specified. For example, only one ``cl::ConsumeAfter`` can be specified per |
| program, there must be at least one `positional argument`_ specified, there must |
| not be any `cl::list`_ positional arguments, and the ``cl::ConsumeAfter`` option |
| should be a `cl::list`_ option. |
| |
| .. _can be changed: |
| .. _Internal vs External Storage: |
| |
| Internal vs External Storage |
| ---------------------------- |
| |
| By default, all command line options automatically hold the value that they |
| parse from the command line. This is very convenient in the common case, |
| especially when combined with the ability to define command line options in the |
| files that use them. This is called the internal storage model. |
| |
| Sometimes, however, it is nice to separate the command line option processing |
| code from the storage of the value parsed. For example, lets say that we have a |
| '``-debug``' option that we would like to use to enable debug information across |
| the entire body of our program. In this case, the boolean value controlling the |
| debug code should be globally accessible (in a header file, for example) yet the |
| command line option processing code should not be exposed to all of these |
| clients (requiring lots of .cpp files to ``#include CommandLine.h``). |
| |
| To do this, set up your .h file with your option, like this for example: |
| |
| .. code-block:: c++ |
| |
| // DebugFlag.h - Get access to the '-debug' command line option |
| // |
| |
| // DebugFlag - This boolean is set to true if the '-debug' command line option |
| // is specified. This should probably not be referenced directly, instead, use |
| // the DEBUG macro below. |
| // |
| extern bool DebugFlag; |
| |
| // DEBUG macro - This macro should be used by code to emit debug information. |
| // In the '-debug' option is specified on the command line, and if this is a |
| // debug build, then the code specified as the option to the macro will be |
| // executed. Otherwise it will not be. |
| #ifdef NDEBUG |
| #define LLVM_DEBUG(X) |
| #else |
| #define LLVM_DEBUG(X) do { if (DebugFlag) { X; } } while (0) |
| #endif |
| |
| This allows clients to blissfully use the ``LLVM_DEBUG()`` macro, or the |
| ``DebugFlag`` explicitly if they want to. Now we just need to be able to set |
| the ``DebugFlag`` boolean when the option is set. To do this, we pass an |
| additional argument to our command line argument processor, and we specify where |
| to fill in with the `cl::location`_ attribute: |
| |
| .. code-block:: c++ |
| |
| bool DebugFlag; // the actual value |
| static cl::opt<bool, true> // The parser |
| Debug("debug", cl::desc("Enable debug output"), cl::Hidden, cl::location(DebugFlag)); |
| |
| In the above example, we specify "``true``" as the second argument to the |
| `cl::opt`_ template, indicating that the template should not maintain a copy of |
| the value itself. In addition to this, we specify the `cl::location`_ |
| attribute, so that ``DebugFlag`` is automatically set. |
| |
| Option Attributes |
| ----------------- |
| |
| This section describes the basic attributes that you can specify on options. |
| |
| * The option name attribute (which is required for all options, except |
| `positional options`_) specifies what the option name is. This option is |
| specified in simple double quotes: |
| |
| .. code-block:: c++ |
| |
| cl::opt<bool> Quiet("quiet"); |
| |
| .. _cl::desc(...): |
| |
| * The **cl::desc** attribute specifies a description for the option to be |
| shown in the ``-help`` output for the program. This attribute supports |
| multi-line descriptions with lines separated by '\n'. |
| |
| .. _cl::value_desc: |
| |
| * The **cl::value_desc** attribute specifies a string that can be used to |
| fine tune the ``-help`` output for a command line option. Look `here`_ for an |
| example. |
| |
| .. _cl::init: |
| |
| * The **cl::init** attribute specifies an initial value for a `scalar`_ |
| option. If this attribute is not specified then the command line option value |
| defaults to the value created by the default constructor for the |
| type. |
| |
| .. warning:: |
| |
| If you specify both **cl::init** and **cl::location** for an option, you |
| must specify **cl::location** first, so that when the command-line parser |
| sees **cl::init**, it knows where to put the initial value. (You will get an |
| error at runtime if you don't put them in the right order.) |
| |
| .. _cl::location: |
| |
| * The **cl::location** attribute where to store the value for a parsed command |
| line option if using external storage. See the section on `Internal vs |
| External Storage`_ for more information. |
| |
| .. _cl::aliasopt: |
| |
| * The **cl::aliasopt** attribute specifies which option a `cl::alias`_ option is |
| an alias for. |
| |
| .. _cl::values: |
| |
| * The **cl::values** attribute specifies the string-to-value mapping to be used |
| by the generic parser. It takes a list of (option, value, description) |
| triplets that specify the option name, the value mapped to, and the |
| description shown in the ``-help`` for the tool. Because the generic parser |
| is used most frequently with enum values, two macros are often useful: |
| |
| #. The **clEnumVal** macro is used as a nice simple way to specify a triplet |
| for an enum. This macro automatically makes the option name be the same as |
| the enum name. The first option to the macro is the enum, the second is |
| the description for the command line option. |
| |
| #. The **clEnumValN** macro is used to specify macro options where the option |
| name doesn't equal the enum name. For this macro, the first argument is |
| the enum value, the second is the flag name, and the second is the |
| description. |
| |
| You will get a compile time error if you try to use cl::values with a parser |
| that does not support it. |
| |
| .. _cl::multi_val: |
| |
| * The **cl::multi_val** attribute specifies that this option takes has multiple |
| values (example: ``-sectalign segname sectname sectvalue``). This attribute |
| takes one unsigned argument - the number of values for the option. This |
| attribute is valid only on ``cl::list`` options (and will fail with compile |
| error if you try to use it with other option types). It is allowed to use all |
| of the usual modifiers on multi-valued options (besides |
| ``cl::ValueDisallowed``, obviously). |
| |
| .. _cl::cat: |
| |
| * The **cl::cat** attribute specifies the option category that the option |
| belongs to. The category should be a `cl::OptionCategory`_ object. |
| |
| .. _cl::callback: |
| |
| * The **cl::callback** attribute specifies a callback function that is |
| called when an option is seen, and can be used to set other options, |
| as in option B implies option A. If the option is a `cl::list`_, |
| and `cl::CommaSeparated`_ is also specified, the callback will fire |
| once for each value. This could be used to validate combinations or |
| selectively set other options. |
| |
| .. code-block:: c++ |
| |
| cl::opt<bool> OptA("a", cl::desc("option a")); |
| cl::opt<bool> OptB( |
| "b", cl::desc("option b -- This option turns on option a"), |
| cl::callback([&](const bool &) { OptA = true; })); |
| cl::list<std::string, cl::list<std::string>> List( |
| "list", |
| cl::desc("option list -- This option turns on options a when " |
| "'foo' is included in list"), |
| cl::CommaSeparated, |
| cl::callback([&](const std::string &Str) { |
| if (Str == "foo") |
| OptA = true; |
| })); |
| |
| Option Modifiers |
| ---------------- |
| |
| Option modifiers are the flags and expressions that you pass into the |
| constructors for `cl::opt`_ and `cl::list`_. These modifiers give you the |
| ability to tweak how options are parsed and how ``-help`` output is generated to |
| fit your application well. |
| |
| These options fall into five main categories: |
| |
| #. Hiding an option from ``-help`` output |
| |
| #. Controlling the number of occurrences required and allowed |
| |
| #. Controlling whether or not a value must be specified |
| |
| #. Controlling other formatting options |
| |
| #. Miscellaneous option modifiers |
| |
| It is not possible to specify two options from the same category (you'll get a |
| runtime error) to a single option, except for options in the miscellaneous |
| category. The CommandLine library specifies defaults for all of these settings |
| that are the most useful in practice and the most common, which mean that you |
| usually shouldn't have to worry about these. |
| |
| Hiding an option from ``-help`` output |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::NotHidden``, ``cl::Hidden``, and ``cl::ReallyHidden`` modifiers are |
| used to control whether or not an option appears in the ``-help`` and |
| ``-help-hidden`` output for the compiled program: |
| |
| .. _cl::NotHidden: |
| |
| * The **cl::NotHidden** modifier (which is the default for `cl::opt`_ and |
| `cl::list`_ options) indicates the option is to appear in both help |
| listings. |
| |
| .. _cl::Hidden: |
| |
| * The **cl::Hidden** modifier (which is the default for `cl::alias`_ options) |
| indicates that the option should not appear in the ``-help`` output, but |
| should appear in the ``-help-hidden`` output. |
| |
| .. _cl::ReallyHidden: |
| |
| * The **cl::ReallyHidden** modifier indicates that the option should not appear |
| in any help output. |
| |
| Controlling the number of occurrences required and allowed |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| This group of options is used to control how many time an option is allowed (or |
| required) to be specified on the command line of your program. Specifying a |
| value for this setting allows the CommandLine library to do error checking for |
| you. |
| |
| The allowed values for this option group are: |
| |
| .. _cl::Optional: |
| |
| * The **cl::Optional** modifier (which is the default for the `cl::opt`_ and |
| `cl::alias`_ classes) indicates that your program will allow either zero or |
| one occurrence of the option to be specified. |
| |
| .. _cl::ZeroOrMore: |
| |
| * The **cl::ZeroOrMore** modifier (which is the default for the `cl::list`_ |
| class) indicates that your program will allow the option to be specified zero |
| or more times. |
| |
| .. _cl::Required: |
| |
| * The **cl::Required** modifier indicates that the specified option must be |
| specified exactly one time. |
| |
| .. _cl::OneOrMore: |
| |
| * The **cl::OneOrMore** modifier indicates that the option must be specified at |
| least one time. |
| |
| * The **cl::ConsumeAfter** modifier is described in the `Positional arguments |
| section`_. |
| |
| If an option is not specified, then the value of the option is equal to the |
| value specified by the `cl::init`_ attribute. If the ``cl::init`` attribute is |
| not specified, the option value is initialized with the default constructor for |
| the data type. |
| |
| If an option is specified multiple times for an option of the `cl::opt`_ class, |
| only the last value will be retained. |
| |
| Controlling whether or not a value must be specified |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| This group of options is used to control whether or not the option allows a |
| value to be present. In the case of the CommandLine library, a value is either |
| specified with an equal sign (e.g. '``-index-depth=17``') or as a trailing |
| string (e.g. '``-o a.out``'). |
| |
| The allowed values for this option group are: |
| |
| .. _cl::ValueOptional: |
| |
| * The **cl::ValueOptional** modifier (which is the default for ``bool`` typed |
| options) specifies that it is acceptable to have a value, or not. A boolean |
| argument can be enabled just by appearing on the command line, or it can have |
| an explicit '``-foo=true``'. If an option is specified with this mode, it is |
| illegal for the value to be provided without the equal sign. Therefore |
| '``-foo true``' is illegal. To get this behavior, you must use |
| the `cl::ValueRequired`_ modifier. |
| |
| .. _cl::ValueRequired: |
| |
| * The **cl::ValueRequired** modifier (which is the default for all other types |
| except for `unnamed alternatives using the generic parser`_) specifies that a |
| value must be provided. This mode informs the command line library that if an |
| option is not provides with an equal sign, that the next argument provided |
| must be the value. This allows things like '``-o a.out``' to work. |
| |
| .. _cl::ValueDisallowed: |
| |
| * The **cl::ValueDisallowed** modifier (which is the default for `unnamed |
| alternatives using the generic parser`_) indicates that it is a runtime error |
| for the user to specify a value. This can be provided to disallow users from |
| providing options to boolean options (like '``-foo=true``'). |
| |
| In general, the default values for this option group work just like you would |
| want them to. As mentioned above, you can specify the `cl::ValueDisallowed`_ |
| modifier to a boolean argument to restrict your command line parser. These |
| options are mostly useful when `extending the library`_. |
| |
| .. _formatting option: |
| |
| Controlling other formatting options |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The formatting option group is used to specify that the command line option has |
| special abilities and is otherwise different from other command line arguments. |
| As usual, you can only specify one of these arguments at most. |
| |
| .. _cl::NormalFormatting: |
| |
| * The **cl::NormalFormatting** modifier (which is the default all options) |
| specifies that this option is "normal". |
| |
| .. _cl::Positional: |
| |
| * The **cl::Positional** modifier specifies that this is a positional argument |
| that does not have a command line option associated with it. See the |
| `Positional Arguments`_ section for more information. |
| |
| * The **cl::ConsumeAfter** modifier specifies that this option is used to |
| capture "interpreter style" arguments. See `this section for more |
| information`_. |
| |
| .. _prefix: |
| .. _cl::Prefix: |
| |
| * The **cl::Prefix** modifier specifies that this option prefixes its value. |
| With 'Prefix' options, the equal sign does not separate the value from the |
| option name specified. Instead, the value is everything after the prefix, |
| including any equal sign if present. This is useful for processing odd |
| arguments like ``-lmalloc`` and ``-L/usr/lib`` in a linker tool or |
| ``-DNAME=value`` in a compiler tool. Here, the '``l``', '``D``' and '``L``' |
| options are normal string (or list) options, that have the **cl::Prefix** |
| modifier added to allow the CommandLine library to recognize them. Note that |
| **cl::Prefix** options must not have the **cl::ValueDisallowed** modifier |
| specified. |
| |
| .. _grouping: |
| .. _cl::Grouping: |
| |
| Controlling options grouping |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The **cl::Grouping** modifier can be combined with any formatting types except |
| for `cl::Positional`_. It is used to implement Unix-style tools (like ``ls``) |
| that have lots of single letter arguments, but only require a single dash. |
| For example, the '``ls -labF``' command actually enables four different options, |
| all of which are single letters. |
| |
| Note that **cl::Grouping** options can have values only if they are used |
| separately or at the end of the groups. For `cl::ValueRequired`_, it is |
| a runtime error if such an option is used elsewhere in the group. |
| |
| The CommandLine library does not restrict how you use the **cl::Prefix** or |
| **cl::Grouping** modifiers, but it is possible to specify ambiguous argument |
| settings. Thus, it is possible to have multiple letter options that are prefix |
| or grouping options, and they will still work as designed. |
| |
| To do this, the CommandLine library uses a greedy algorithm to parse the input |
| option into (potentially multiple) prefix and grouping options. The strategy |
| basically looks like this: |
| |
| :: |
| |
| parse(string OrigInput) { |
| |
| 1. string Input = OrigInput; |
| 2. if (isOption(Input)) return getOption(Input).parse(); // Normal option |
| 3. while (!Input.empty() && !isOption(Input)) Input.pop_back(); // Remove the last letter |
| 4. while (!Input.empty()) { |
| string MaybeValue = OrigInput.substr(Input.length()) |
| if (getOption(Input).isPrefix()) |
| return getOption(Input).parse(MaybeValue) |
| if (!MaybeValue.empty() && MaybeValue[0] == '=') |
| return getOption(Input).parse(MaybeValue.substr(1)) |
| if (!getOption(Input).isGrouping()) |
| return error() |
| getOption(Input).parse() |
| Input = OrigInput = MaybeValue |
| while (!Input.empty() && !isOption(Input)) Input.pop_back(); |
| if (!Input.empty() && !getOption(Input).isGrouping()) |
| return error() |
| } |
| 5. if (!OrigInput.empty()) error(); |
| |
| } |
| |
| Miscellaneous option modifiers |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The miscellaneous option modifiers are the only flags where you can specify more |
| than one flag from the set: they are not mutually exclusive. These flags |
| specify boolean properties that modify the option. |
| |
| .. _cl::CommaSeparated: |
| |
| * The **cl::CommaSeparated** modifier indicates that any commas specified for an |
| option's value should be used to split the value up into multiple values for |
| the option. For example, these two options are equivalent when |
| ``cl::CommaSeparated`` is specified: "``-foo=a -foo=b -foo=c``" and |
| "``-foo=a,b,c``". This option only makes sense to be used in a case where the |
| option is allowed to accept one or more values (i.e. it is a `cl::list`_ |
| option). |
| |
| .. _cl::DefaultOption: |
| |
| * The **cl::DefaultOption** modifier is used to specify that the option is a |
| default that can be overridden by application specific parsers. For example, |
| the ``-help`` alias, ``-h``, is registered this way, so it can be overridden |
| by applications that need to use the ``-h`` option for another purpose, |
| either as a regular option or an alias for another option. |
| |
| .. _cl::PositionalEatsArgs: |
| |
| * The **cl::PositionalEatsArgs** modifier (which only applies to positional |
| arguments, and only makes sense for lists) indicates that positional argument |
| should consume any strings after it (including strings that start with a "-") |
| up until another recognized positional argument. For example, if you have two |
| "eating" positional arguments, "``pos1``" and "``pos2``", the string "``-pos1 |
| -foo -bar baz -pos2 -bork``" would cause the "``-foo -bar -baz``" strings to |
| be applied to the "``-pos1``" option and the "``-bork``" string to be applied |
| to the "``-pos2``" option. |
| |
| .. _cl::Sink: |
| |
| * The **cl::Sink** modifier is used to handle unknown options. If there is at |
| least one option with ``cl::Sink`` modifier specified, the parser passes |
| unrecognized option strings to it as values instead of signaling an error. As |
| with ``cl::CommaSeparated``, this modifier only makes sense with a `cl::list`_ |
| option. |
| |
| .. _response files: |
| |
| Response files |
| ^^^^^^^^^^^^^^ |
| |
| Some systems, such as certain variants of Microsoft Windows and some older |
| Unices have a relatively low limit on command-line length. It is therefore |
| customary to use the so-called 'response files' to circumvent this |
| restriction. These files are mentioned on the command-line (using the "@file") |
| syntax. The program reads these files and inserts the contents into argv, |
| thereby working around the command-line length limits. |
| |
| Top-Level Classes and Functions |
| ------------------------------- |
| |
| Despite all of the built-in flexibility, the CommandLine option library really |
| only consists of one function `cl::ParseCommandLineOptions`_ and three main |
| classes: `cl::opt`_, `cl::list`_, and `cl::alias`_. This section describes |
| these three classes in detail. |
| |
| .. _cl::getRegisteredOptions: |
| |
| The ``cl::getRegisteredOptions`` function |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::getRegisteredOptions`` function is designed to give a programmer |
| access to declared non-positional command line options so that how they appear |
| in ``-help`` can be modified prior to calling `cl::ParseCommandLineOptions`_. |
| Note this method should not be called during any static initialisation because |
| it cannot be guaranteed that all options will have been initialised. Hence it |
| should be called from ``main``. |
| |
| This function can be used to gain access to options declared in libraries that |
| the tool writer may not have direct access to. |
| |
| The function retrieves a :ref:`StringMap <dss_stringmap>` that maps the option |
| string (e.g. ``-help``) to an ``Option*``. |
| |
| Here is an example of how the function could be used: |
| |
| .. code-block:: c++ |
| |
| using namespace llvm; |
| int main(int argc, char **argv) { |
| cl::OptionCategory AnotherCategory("Some options"); |
| |
| StringMap<cl::Option*> &Map = cl::getRegisteredOptions(); |
| |
| //Unhide useful option and put it in a different category |
| assert(Map.count("print-all-options") > 0); |
| Map["print-all-options"]->setHiddenFlag(cl::NotHidden); |
| Map["print-all-options"]->setCategory(AnotherCategory); |
| |
| //Hide an option we don't want to see |
| assert(Map.count("enable-no-infs-fp-math") > 0); |
| Map["enable-no-infs-fp-math"]->setHiddenFlag(cl::Hidden); |
| |
| //Change --version to --show-version |
| assert(Map.count("version") > 0); |
| Map["version"]->setArgStr("show-version"); |
| |
| //Change --help description |
| assert(Map.count("help") > 0); |
| Map["help"]->setDescription("Shows help"); |
| |
| cl::ParseCommandLineOptions(argc, argv, "This is a small program to demo the LLVM CommandLine API"); |
| ... |
| } |
| |
| |
| .. _cl::ParseCommandLineOptions: |
| |
| The ``cl::ParseCommandLineOptions`` function |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::ParseCommandLineOptions`` function is designed to be called directly |
| from ``main``, and is used to fill in the values of all of the command line |
| option variables once ``argc`` and ``argv`` are available. |
| |
| The ``cl::ParseCommandLineOptions`` function requires two parameters (``argc`` |
| and ``argv``), but may also take an optional third parameter which holds |
| `additional extra text`_ to emit when the ``-help`` option is invoked. |
| |
| The ``cl::SetVersionPrinter`` function |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::SetVersionPrinter`` function is designed to be called directly from |
| ``main`` and *before* ``cl::ParseCommandLineOptions``. Its use is optional. It |
| simply arranges for a function to be called in response to the ``--version`` |
| option instead of having the ``CommandLine`` library print out the usual version |
| string for LLVM. This is useful for programs that are not part of LLVM but wish |
| to use the ``CommandLine`` facilities. Such programs should just define a small |
| function that takes no arguments and returns ``void`` and that prints out |
| whatever version information is appropriate for the program. Pass the address of |
| that function to ``cl::SetVersionPrinter`` to arrange for it to be called when |
| the ``--version`` option is given by the user. |
| |
| .. _cl::opt: |
| .. _scalar: |
| |
| The ``cl::opt`` class |
| ^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::opt`` class is the class used to represent scalar command line |
| options, and is the one used most of the time. It is a templated class which |
| can take up to three arguments (all except for the first have default values |
| though): |
| |
| .. code-block:: c++ |
| |
| namespace cl { |
| template <class DataType, bool ExternalStorage = false, |
| class ParserClass = parser<DataType> > |
| class opt; |
| } |
| |
| The first template argument specifies what underlying data type the command line |
| argument is, and is used to select a default parser implementation. The second |
| template argument is used to specify whether the option should contain the |
| storage for the option (the default) or whether external storage should be used |
| to contain the value parsed for the option (see `Internal vs External Storage`_ |
| for more information). |
| |
| The third template argument specifies which parser to use. The default value |
| selects an instantiation of the ``parser`` class based on the underlying data |
| type of the option. In general, this default works well for most applications, |
| so this option is only used when using a `custom parser`_. |
| |
| .. _lists of arguments: |
| .. _cl::list: |
| |
| The ``cl::list`` class |
| ^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::list`` class is the class used to represent a list of command line |
| options. It too is a templated class which can take up to three arguments: |
| |
| .. code-block:: c++ |
| |
| namespace cl { |
| template <class DataType, class Storage = bool, |
| class ParserClass = parser<DataType> > |
| class list; |
| } |
| |
| This class works the exact same as the `cl::opt`_ class, except that the second |
| argument is the **type** of the external storage, not a boolean value. For this |
| class, the marker type '``bool``' is used to indicate that internal storage |
| should be used. |
| |
| .. _cl::bits: |
| |
| The ``cl::bits`` class |
| ^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::bits`` class is the class used to represent a list of command line |
| options in the form of a bit vector. It is also a templated class which can |
| take up to three arguments: |
| |
| .. code-block:: c++ |
| |
| namespace cl { |
| template <class DataType, class Storage = bool, |
| class ParserClass = parser<DataType> > |
| class bits; |
| } |
| |
| This class works the exact same as the `cl::list`_ class, except that the second |
| argument must be of **type** ``unsigned`` if external storage is used. |
| |
| .. _cl::alias: |
| |
| The ``cl::alias`` class |
| ^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::alias`` class is a nontemplated class that is used to form aliases for |
| other arguments. |
| |
| .. code-block:: c++ |
| |
| namespace cl { |
| class alias; |
| } |
| |
| The `cl::aliasopt`_ attribute should be used to specify which option this is an |
| alias for. Alias arguments default to being `cl::Hidden`_, and use the aliased |
| options parser to do the conversion from string to data. |
| |
| .. _cl::extrahelp: |
| |
| The ``cl::extrahelp`` class |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::extrahelp`` class is a nontemplated class that allows extra help text |
| to be printed out for the ``-help`` option. |
| |
| .. code-block:: c++ |
| |
| namespace cl { |
| struct extrahelp; |
| } |
| |
| To use the extrahelp, simply construct one with a ``const char*`` parameter to |
| the constructor. The text passed to the constructor will be printed at the |
| bottom of the help message, verbatim. Note that multiple ``cl::extrahelp`` |
| **can** be used, but this practice is discouraged. If your tool needs to print |
| additional help information, put all that help into a single ``cl::extrahelp`` |
| instance. |
| |
| For example: |
| |
| .. code-block:: c++ |
| |
| cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); |
| |
| .. _cl::OptionCategory: |
| |
| The ``cl::OptionCategory`` class |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The ``cl::OptionCategory`` class is a simple class for declaring |
| option categories. |
| |
| .. code-block:: c++ |
| |
| namespace cl { |
| class OptionCategory; |
| } |
| |
| An option category must have a name and optionally a description which are |
| passed to the constructor as ``const char*``. |
| |
| Note that declaring an option category and associating it with an option before |
| parsing options (e.g. statically) will change the output of ``-help`` from |
| uncategorized to categorized. If an option category is declared but not |
| associated with an option then it will be hidden from the output of ``-help`` |
| but will be shown in the output of ``-help-hidden``. |
| |
| .. _different parser: |
| .. _discussed previously: |
| |
| Builtin parsers |
| --------------- |
| |
| Parsers control how the string value taken from the command line is translated |
| into a typed value, suitable for use in a C++ program. By default, the |
| CommandLine library uses an instance of ``parser<type>`` if the command line |
| option specifies that it uses values of type '``type``'. Because of this, |
| custom option processing is specified with specializations of the '``parser``' |
| class. |
| |
| The CommandLine library provides the following builtin parser specializations, |
| which are sufficient for most applications. It can, however, also be extended to |
| work with new data types and new ways of interpreting the same data. See the |
| `Writing a Custom Parser`_ for more details on this type of library extension. |
| |
| .. _enums: |
| .. _cl::parser: |
| |
| * The generic ``parser<t>`` parser can be used to map strings values to any data |
| type, through the use of the `cl::values`_ property, which specifies the |
| mapping information. The most common use of this parser is for parsing enum |
| values, which allows you to use the CommandLine library for all of the error |
| checking to make sure that only valid enum values are specified (as opposed to |
| accepting arbitrary strings). Despite this, however, the generic parser class |
| can be used for any data type. |
| |
| .. _boolean flags: |
| .. _bool parser: |
| |
| * The **parser<bool> specialization** is used to convert boolean strings to a |
| boolean value. Currently accepted strings are "``true``", "``TRUE``", |
| "``True``", "``1``", "``false``", "``FALSE``", "``False``", and "``0``". |
| |
| * The **parser<boolOrDefault> specialization** is used for cases where the value |
| is boolean, but we also need to know whether the option was specified at all. |
| boolOrDefault is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. |
| This parser accepts the same strings as **``parser<bool>``**. |
| |
| .. _strings: |
| |
| * The **parser<string> specialization** simply stores the parsed string into the |
| string value specified. No conversion or modification of the data is |
| performed. |
| |
| .. _integers: |
| .. _int: |
| |
| * The **parser<int> specialization** uses the C ``strtol`` function to parse the |
| string input. As such, it will accept a decimal number (with an optional '+' |
| or '-' prefix) which must start with a non-zero digit. It accepts octal |
| numbers, which are identified with a '``0``' prefix digit, and hexadecimal |
| numbers with a prefix of '``0x``' or '``0X``'. |
| |
| .. _doubles: |
| .. _float: |
| .. _double: |
| |
| * The **parser<double>** and **parser<float> specializations** use the standard |
| C ``strtod`` function to convert floating point strings into floating point |
| values. As such, a broad range of string formats is supported, including |
| exponential notation (ex: ``1.7e15``) and properly supports locales. |
| |
| .. _Extension Guide: |
| .. _extending the library: |
| |
| Extension Guide |
| =============== |
| |
| Although the CommandLine library has a lot of functionality built into it |
| already (as discussed previously), one of its true strengths lie in its |
| extensibility. This section discusses how the CommandLine library works under |
| the covers and illustrates how to do some simple, common, extensions. |
| |
| .. _Custom parsers: |
| .. _custom parser: |
| .. _Writing a Custom Parser: |
| |
| Writing a custom parser |
| ----------------------- |
| |
| One of the simplest and most common extensions is the use of a custom parser. |
| As `discussed previously`_, parsers are the portion of the CommandLine library |
| that turns string input from the user into a particular parsed data type, |
| validating the input in the process. |
| |
| There are two ways to use a new parser: |
| |
| #. Specialize the `cl::parser`_ template for your custom data type. |
| |
| This approach has the advantage that users of your custom data type will |
| automatically use your custom parser whenever they define an option with a |
| value type of your data type. The disadvantage of this approach is that it |
| doesn't work if your fundamental data type is something that is already |
| supported. |
| |
| #. Write an independent class, using it explicitly from options that need it. |
| |
| This approach works well in situations where you would line to parse an |
| option using special syntax for a not-very-special data-type. The drawback |
| of this approach is that users of your parser have to be aware that they are |
| using your parser instead of the builtin ones. |
| |
| To guide the discussion, we will discuss a custom parser that accepts file |
| sizes, specified with an optional unit after the numeric size. For example, we |
| would like to parse "102kb", "41M", "1G" into the appropriate integer value. In |
| this case, the underlying data type we want to parse into is '``unsigned``'. We |
| choose approach #2 above because we don't want to make this the default for all |
| ``unsigned`` options. |
| |
| To start out, we declare our new ``FileSizeParser`` class: |
| |
| .. code-block:: c++ |
| |
| struct FileSizeParser : public cl::parser<unsigned> { |
| // parse - Return true on error. |
| bool parse(cl::Option &O, StringRef ArgName, const std::string &ArgValue, |
| unsigned &Val); |
| }; |
| |
| Our new class inherits from the ``cl::parser`` template class to fill in |
| the default, boiler plate code for us. We give it the data type that we parse |
| into, the last argument to the ``parse`` method, so that clients of our custom |
| parser know what object type to pass in to the parse method. (Here we declare |
| that we parse into '``unsigned``' variables.) |
| |
| For most purposes, the only method that must be implemented in a custom parser |
| is the ``parse`` method. The ``parse`` method is called whenever the option is |
| invoked, passing in the option itself, the option name, the string to parse, and |
| a reference to a return value. If the string to parse is not well-formed, the |
| parser should output an error message and return true. Otherwise it should |
| return false and set '``Val``' to the parsed value. In our example, we |
| implement ``parse`` as: |
| |
| .. code-block:: c++ |
| |
| bool FileSizeParser::parse(cl::Option &O, StringRef ArgName, |
| const std::string &Arg, unsigned &Val) { |
| const char *ArgStart = Arg.c_str(); |
| char *End; |
| |
| // Parse integer part, leaving 'End' pointing to the first non-integer char |
| Val = (unsigned)strtol(ArgStart, &End, 0); |
| |
| while (1) { |
| switch (*End++) { |
| case 0: return false; // No error |
| case 'i': // Ignore the 'i' in KiB if people use that |
| case 'b': case 'B': // Ignore B suffix |
| break; |
| |
| case 'g': case 'G': Val *= 1024*1024*1024; break; |
| case 'm': case 'M': Val *= 1024*1024; break; |
| case 'k': case 'K': Val *= 1024; break; |
| |
| default: |
| // Print an error message if unrecognized character! |
| return O.error("'" + Arg + "' value invalid for file size argument!"); |
| } |
| } |
| } |
| |
| This function implements a very simple parser for the kinds of strings we are |
| interested in. Although it has some holes (it allows "``123KKK``" for example), |
| it is good enough for this example. Note that we use the option itself to print |
| out the error message (the ``error`` method always returns true) in order to get |
| a nice error message (shown below). Now that we have our parser class, we can |
| use it like this: |
| |
| .. code-block:: c++ |
| |
| static cl::opt<unsigned, false, FileSizeParser> |
| MFS("max-file-size", cl::desc("Maximum file size to accept"), |
| cl::value_desc("size")); |
| |
| Which adds this to the output of our program: |
| |
| :: |
| |
| OPTIONS: |
| -help - display available options (-help-hidden for more) |
| ... |
| -max-file-size=<size> - Maximum file size to accept |
| |
| And we can test that our parse works correctly now (the test program just prints |
| out the max-file-size argument value): |
| |
| :: |
| |
| $ ./test |
| MFS: 0 |
| $ ./test -max-file-size=123MB |
| MFS: 128974848 |
| $ ./test -max-file-size=3G |
| MFS: 3221225472 |
| $ ./test -max-file-size=dog |
| -max-file-size option: 'dog' value invalid for file size argument! |
| |
| It looks like it works. The error message that we get is nice and helpful, and |
| we seem to accept reasonable file sizes. This wraps up the "custom parser" |
| tutorial. |
| |
| Exploiting external storage |
| --------------------------- |
| |
| Several of the LLVM libraries define static ``cl::opt`` instances that will |
| automatically be included in any program that links with that library. This is |
| a feature. However, sometimes it is necessary to know the value of the command |
| line option outside of the library. In these cases the library does or should |
| provide an external storage location that is accessible to users of the |
| library. Examples of this include the ``llvm::DebugFlag`` exported by the |
| ``lib/Support/Debug.cpp`` file and the ``llvm::TimePassesIsEnabled`` flag |
| exported by the ``lib/IR/PassManager.cpp`` file. |
| |
| .. todo:: |
| |
| TODO: complete this section |
| |
| .. _dynamically loaded options: |
| |
| Dynamically adding command line options |
| --------------------------------------- |
| |
| .. todo:: |
| |
| TODO: fill in this section |