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| author | mike-m <mikem.llvm@gmail.com> | 2010-05-07 00:28:04 +0000 |
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| committer | mike-m <mikem.llvm@gmail.com> | 2010-05-07 00:28:04 +0000 |
| commit | e2c3a49c8029ebd9ef530101cc24c66562e3dff5 (patch) | |
| tree | 91bf9600cc8df90cf99751a8f8bafc317cffc91e /docs/CommandLine.html | |
| parent | c10b5afbe8138b0fdf3af4ed3e1ddf96cf3cb4cb (diff) | |
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diff --git a/docs/CommandLine.html b/docs/CommandLine.html new file mode 100644 index 0000000..47ab2cc --- /dev/null +++ b/docs/CommandLine.html @@ -0,0 +1,1979 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> + <title>CommandLine 2.0 Library Manual</title> + <link rel="stylesheet" href="llvm.css" type="text/css"> +</head> +<body> + +<div class="doc_title"> + CommandLine 2.0 Library Manual +</div> + +<ol> + <li><a href="#introduction">Introduction</a></li> + + <li><a href="#quickstart">Quick Start Guide</a> + <ol> + <li><a href="#bool">Boolean Arguments</a></li> + <li><a href="#alias">Argument Aliases</a></li> + <li><a href="#onealternative">Selecting an alternative from a + set of possibilities</a></li> + <li><a href="#namedalternatives">Named alternatives</a></li> + <li><a href="#list">Parsing a list of options</a></li> + <li><a href="#bits">Collecting options as a set of flags</a></li> + <li><a href="#description">Adding freeform text to help output</a></li> + </ol></li> + + <li><a href="#referenceguide">Reference Guide</a> + <ol> + <li><a href="#positional">Positional Arguments</a> + <ul> + <li><a href="#--">Specifying positional options with hyphens</a></li> + <li><a href="#getPosition">Determining absolute position with + getPosition</a></li> + <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> + modifier</a></li> + </ul></li> + + <li><a href="#storage">Internal vs External Storage</a></li> + + <li><a href="#attributes">Option Attributes</a></li> + + <li><a href="#modifiers">Option Modifiers</a> + <ul> + <li><a href="#hiding">Hiding an option from <tt>-help</tt> + output</a></li> + <li><a href="#numoccurrences">Controlling the number of occurrences + required and allowed</a></li> + <li><a href="#valrequired">Controlling whether or not a value must be + specified</a></li> + <li><a href="#formatting">Controlling other formatting options</a></li> + <li><a href="#misc">Miscellaneous option modifiers</a></li> + <li><a href="#response">Response files</a></li> + </ul></li> + + <li><a href="#toplevel">Top-Level Classes and Functions</a> + <ul> + <li><a href="#cl::ParseCommandLineOptions">The + <tt>cl::ParseCommandLineOptions</tt> function</a></li> + <li><a href="#cl::ParseEnvironmentOptions">The + <tt>cl::ParseEnvironmentOptions</tt> function</a></li> + <li><a href="#cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt> + function</a></li> + <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li> + <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li> + <li><a href="#cl::bits">The <tt>cl::bits</tt> class</a></li> + <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li> + <li><a href="#cl::extrahelp">The <tt>cl::extrahelp</tt> class</a></li> + </ul></li> + + <li><a href="#builtinparsers">Builtin parsers</a> + <ul> + <li><a href="#genericparser">The Generic <tt>parser<t></tt> + parser</a></li> + <li><a href="#boolparser">The <tt>parser<bool></tt> + specialization</a></li> + <li><a href="#boolOrDefaultparser">The <tt>parser<boolOrDefault></tt> + specialization</a></li> + <li><a href="#stringparser">The <tt>parser<string></tt> + specialization</a></li> + <li><a href="#intparser">The <tt>parser<int></tt> + specialization</a></li> + <li><a href="#doubleparser">The <tt>parser<double></tt> and + <tt>parser<float></tt> specializations</a></li> + </ul></li> + </ol></li> + <li><a href="#extensionguide">Extension Guide</a> + <ol> + <li><a href="#customparser">Writing a custom parser</a></li> + <li><a href="#explotingexternal">Exploiting external storage</a></li> + <li><a href="#dynamicopts">Dynamically adding command line + options</a></li> + </ol></li> +</ol> + +<div class="doc_author"> + <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p> +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"> + <a name="introduction">Introduction</a> +</div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>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 <a href="#storage">can be +changed</a>).</p> + +<p>Although there are a <b>lot</b> 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:</p> + +<ol> +<li>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 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).</li> + +<li>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.</li> + +<li>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 <b>any</b> boilerplate +code.</li> + +<li>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 <a href="#dynamicopts">dynamically +loaded options</a> trivial.</li> + +<li>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.</li> + +<li>Powerful: The CommandLine library supports many different types of +arguments, from simple <a href="#boolparser">boolean flags</a> to <a +href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a +href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a +href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of +arguments</a>. This is possible because CommandLine is...</li> + +<li>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. <a href="#customparser">Custom parsers</a> are no problem.</li> + +<li>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 +<tt>-help</tt> option that shows the available command line options for your +tool. Additionally, it does most of the basic correctness checking for +you.</li> + +<li>Capable: The CommandLine library can handle lots of different forms of +options often found in real programs. For example, <a +href="#positional">positional</a> arguments, <tt>ls</tt> style <a +href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls +-lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a> +options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a +href="#cl::ConsumeAfter">interpreter style options</a>.</li> + +</ol> + +<p>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. If it is failing in some area +(or you want an extension to the library), nag the author, <a +href="mailto:sabre@nondot.org">Chris Lattner</a>.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"> + <a name="quickstart">Quick Start Guide</a> +</div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>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.</p> + +<p>To start out, you need to include the CommandLine header file into your +program:</p> + +<div class="doc_code"><pre> + #include "llvm/Support/CommandLine.h" +</pre></div> + +<p>Additionally, you need to add this as the first line of your main +program:</p> + +<div class="doc_code"><pre> +int main(int argc, char **argv) { + <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv); + ... +} +</pre></div> + +<p>... which actually parses the arguments and fills in the variable +declarations.</p> + +<p>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 '<tt>-o <filename></tt>' option +to specify where to put the output. With the CommandLine library, this is +represented like this:</p> + +<a name="value_desc_example"></a> +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><string> OutputFilename("<i>o</i>", <a href="#cl::desc">cl::desc</a>("<i>Specify output filename</i>"), <a href="#cl::value_desc">cl::value_desc</a>("<i>filename</i>")); +</pre></div> + +<p>This declares a global variable "<tt>OutputFilename</tt>" that is used to +capture the result of the "<tt>o</tt>" argument (first parameter). We specify +that this is a simple scalar option by using the "<tt><a +href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a +href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library +that the data type that we are parsing is a string.</p> + +<p>The second and third parameters (which are optional) are used to specify what +to output for the "<tt>-help</tt>" option. In this case, we get a line that +looks like this:</p> + +<div class="doc_code"><pre> +USAGE: compiler [options] + +OPTIONS: + -help - display available options (-help-hidden for more) + <b>-o <filename> - Specify output filename</b> +</pre></div> + +<p>Because we specified that the command line option should parse using the +<tt>string</tt> 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:</p> + +<div class="doc_code"><pre> + ... + std::ofstream Output(OutputFilename.c_str()); + if (Output.good()) ... + ... +</pre></div> + +<p>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 <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so +there are no positional dependencies to remember. The available options are +discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p> + +<p>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 <tt>-filename.c</tt>). To support this +style of argument, the CommandLine library allows for <a +href="#positional">positional</a> 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:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>")); +</pre></div> + +<p>This declaration indicates that the first positional argument should be +treated as the input filename. Here we use the <tt><a +href="#cl::init">cl::init</a></tt> 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 <tt><a href="#cl::init">cl::init</a></tt> 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 <tt><a +href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the +<tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <b><a href="#cl::Required">cl::Required</a></b>); +</pre></div> + +<p>Again, the CommandLine library does not require the options to be specified +in any particular order, so the above declaration is equivalent to:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::Required">cl::Required</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>")); +</pre></div> + +<p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> 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 <tt>-help</tt> option synopsis is now +extended to:</p> + +<div class="doc_code"><pre> +USAGE: compiler [options] <b><input file></b> + +OPTIONS: + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename +</pre></div> + +<p>... indicating that an input filename is expected.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="bool">Boolean Arguments</a> +</div> + +<div class="doc_text"> + +<p>In addition to input and output filenames, we would like the compiler example +to support three boolean flags: "<tt>-f</tt>" to force writing binary output to +a terminal, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for +backwards compatibility with some of our users. We can support these by +declaring options of boolean type like this:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable binary output on terminals</i>")); +<a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>")); +<a href="#cl::opt">cl::opt</a><bool> Quiet2("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"), <a href="#cl::Hidden">cl::Hidden</a>); +</pre></div> + +<p>This does what you would expect: it declares three boolean variables +("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these +options. Note that the "<tt>-q</tt>" option is specified with the "<a +href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it +from being shown by the standard "<tt>-help</tt>" output (note that it is still +shown in the "<tt>-help-hidden</tt>" output).</p> + +<p>The CommandLine library uses a <a href="#builtinparsers">different parser</a> +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 +"<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the +following inputs:</p> + +<div class="doc_code"><pre> + 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 +</pre></div> + +<p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns +the string values into boolean values, and rejects things like '<tt>compiler +-f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a +href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work +like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C +library calls to parse the string value into the specified data type.</p> + +<p>With the declarations above, "<tt>compiler -help</tt>" emits this:</p> + +<div class="doc_code"><pre> +USAGE: compiler [options] <input file> + +OPTIONS: + <b>-f - Enable binary output on terminals</b> + -o - Override output filename + <b>-quiet - Don't print informational messages</b> + -help - display available options (-help-hidden for more) +</pre></div> + +<p>and "<tt>compiler -help-hidden</tt>" prints this:</p> + +<div class="doc_code"><pre> +USAGE: compiler [options] <input file> + +OPTIONS: + -f - Enable binary output on terminals + -o - Override output filename + <b>-q - Don't print informational messages</b> + -quiet - Don't print informational messages + -help - display available options (-help-hidden for more) +</pre></div> + +<p>This brief example has shown you how to use the '<tt><a +href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line +arguments. In addition to simple scalar arguments, the CommandLine library also +provides primitives to support CommandLine option <a href="#alias">aliases</a>, +and <a href="#list">lists</a> of options.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="alias">Argument Aliases</a> +</div> + +<div class="doc_text"> + +<p>So far, the example works well, except for the fact that we need to check the +quiet condition like this now:</p> + +<div class="doc_code"><pre> +... + if (!Quiet && !Quiet2) printInformationalMessage(...); +... +</pre></div> + +<p>... which is a real pain! Instead of defining two values for the same +condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>" +option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing +a value itself:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>")); +<a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>")); +<a href="#cl::alias">cl::alias</a> QuietA("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Alias for -quiet</i>"), <a href="#cl::aliasopt">cl::aliasopt</a>(Quiet)); +</pre></div> + +<p>The third line (which is the only one we modified from above) defines a +"<tt>-q</tt>" alias that updates the "<tt>Quiet</tt>" variable (as specified by +the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is +specified. Because aliases do not hold state, the only thing the program has to +query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is +that they automatically hide themselves from the <tt>-help</tt> output +(although, again, they are still visible in the <tt>-help-hidden +output</tt>).</p> + +<p>Now the application code can simply use:</p> + +<div class="doc_code"><pre> +... + if (!Quiet) printInformationalMessage(...); +... +</pre></div> + +<p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>" +can be used to specify an alternative name for any variable type, and has many +uses.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="onealternative">Selecting an alternative from a set of + possibilities</a> +</div> + +<div class="doc_text"> + +<p>So far we have seen how the CommandLine library handles builtin types like +<tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle +things it doesn't know about, like enums or '<tt>int*</tt>'s?</p> + +<p>The answer is that it uses a table-driven generic parser (unless you specify +your own parser, as described in the <a href="#extensionguide">Extension +Guide</a>). This parser maps literal strings to whatever type is required, and +requires you to tell it what this mapping should be.</p> + +<p>Let's say that we would like to add four optimization levels to our +optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>", +"<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean +options like above, but there are several problems with this strategy:</p> + +<ol> +<li>A user could specify more than one of the options at a time, for example, +"<tt>compiler -O3 -O2</tt>". The CommandLine library would not be able to +catch this erroneous input for us.</li> + +<li>We would have to test 4 different variables to see which ones are set.</li> + +<li>This doesn't map to the numeric levels that we want... so we cannot easily +see if some level >= "<tt>-O1</tt>" is enabled.</li> + +</ol> + +<p>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:</p> + +<div class="doc_code"><pre> +enum OptLevel { + g, O1, O2, O3 +}; + +<a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"), + <a href="#cl::values">cl::values</a>( + clEnumVal(g , "<i>No optimizations, enable debugging</i>"), + clEnumVal(O1, "<i>Enable trivial optimizations</i>"), + clEnumVal(O2, "<i>Enable default optimizations</i>"), + clEnumVal(O3, "<i>Enable expensive optimizations</i>"), + clEnumValEnd)); + +... + if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); +... +</pre></div> + +<p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the +"<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values +that are listed in the declaration (Note that the declaration list must be +terminated with the "<tt>clEnumValEnd</tt>" argument!). 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 "<tt>clEnumVal</tt>" macros ensure that the +command line arguments matched the enum values. With this option added, our +help output now is:</p> + +<div class="doc_code"><pre> +USAGE: compiler [options] <input file> + +OPTIONS: + <b>Choose optimization level: + -g - No optimizations, enable debugging + -O1 - Enable trivial optimizations + -O2 - Enable default optimizations + -O3 - Enable expensive optimizations</b> + -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 +</pre></div> + +<p>In this case, it is sort of awkward that flag names correspond directly to +enum names, because we probably don't want a enum definition named "<tt>g</tt>" +in our program. Because of this, we can alternatively write this example like +this:</p> + +<div class="doc_code"><pre> +enum OptLevel { + Debug, O1, O2, O3 +}; + +<a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"), + <a href="#cl::values">cl::values</a>( + clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"), + clEnumVal(O1 , "<i>Enable trivial optimizations</i>"), + clEnumVal(O2 , "<i>Enable default optimizations</i>"), + clEnumVal(O3 , "<i>Enable expensive optimizations</i>"), + clEnumValEnd)); + +... + if (OptimizationLevel == Debug) outputDebugInfo(...); +... +</pre></div> + +<p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", 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.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="namedalternatives">Named Alternatives</a> +</div> + +<div class="doc_text"> + +<p>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: +"<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>", +"<tt>--debug-level=detailed</tt>". 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:</p> + +<div class="doc_code"><pre> +enum DebugLev { + nodebuginfo, quick, detailed +}; + +// Enable Debug Options to be specified on the command line +<a href="#cl::opt">cl::opt</a><DebugLev> DebugLevel("<i>debug_level</i>", <a href="#cl::desc">cl::desc</a>("<i>Set the debugging level:</i>"), + <a href="#cl::values">cl::values</a>( + clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"), + clEnumVal(quick, "<i>enable quick debug information</i>"), + clEnumVal(detailed, "<i>enable detailed debug information</i>"), + clEnumValEnd)); +</pre></div> + +<p>This definition defines an enumerated command line variable of type "<tt>enum +DebugLev</tt>", 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 "<tt>-help</tt>" option:</p> + +<div class="doc_code"><pre> +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 + <b>-debug_level - Set the debugging level: + =none - disable debug information + =quick - enable quick debug information + =detailed - enable detailed debug information</b> + -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 +</pre></div> + +<p>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 (<tt>"debug_level"</tt>), 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.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="list">Parsing a list of options</a> +</div> + +<div class="doc_text"> + +<p>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 <b>list</b> of optimizations to perform, allowing duplicates. For example, we +might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In +this case, the order of the arguments and the number of appearances is very +important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>" +template is for. First, start by defining an enum of the optimizations that you +would like to perform:</p> + +<div class="doc_code"><pre> +enum Opts { + // 'inline' is a C++ keyword, so name it 'inlining' + dce, constprop, inlining, strip +}; +</pre></div> + +<p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p> + +<div class="doc_code"><pre> +<a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"), + <a href="#cl::values">cl::values</a>( + clEnumVal(dce , "<i>Dead Code Elimination</i>"), + clEnumVal(constprop , "<i>Constant Propagation</i>"), + clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"), + clEnumVal(strip , "<i>Strip Symbols</i>"), + clEnumValEnd)); +</pre></div> + +<p>This defines a variable that is conceptually of the type +"<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard +vector methods:</p> + +<div class="doc_code"><pre> + for (unsigned i = 0; i != OptimizationList.size(); ++i) + switch (OptimizationList[i]) + ... +</pre></div> + +<p>... to iterate through the list of options specified.</p> + +<p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is +completely general and may be used with any data types or other arguments that +you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" 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 '<tt>.o</tt>' files, and needs to +capture them into a list. This is naturally specified as:</p> + +<div class="doc_code"><pre> +... +<a href="#cl::list">cl::list</a><std::string> InputFilenames(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<Input files>"), <a href="#cl::OneOrMore">cl::OneOrMore</a>); +... +</pre></div> + +<p>This variable works just like a "<tt>vector<string></tt>" object. As +such, accessing the list is simple, just like above. In this example, we used +the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the +CommandLine library that it is an error if the user does not specify any +<tt>.o</tt> files on our command line. Again, this just reduces the amount of +checking we have to do.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="bits">Collecting options as a set of flags</a> +</div> + +<div class="doc_text"> + +<p>Instead of collecting sets of options in a list, it is also possible to +gather information for enum values in a <b>bit vector</b>. The representation used by +the <a href="#bits"><tt>cl::bits</tt></a> class is an <tt>unsigned</tt> +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:</p> + +<div class="doc_code"><pre> + <i>bits</i> |= 1 << (unsigned)<i>enum</i>; +</pre></div> + +<p>Options that are specified multiple times are redundant. Any instances after +the first are discarded.</p> + +<p>Reworking the above list example, we could replace <a href="#list"> +<tt>cl::list</tt></a> with <a href="#bits"><tt>cl::bits</tt></a>:</p> + +<div class="doc_code"><pre> +<a href="#cl::bits">cl::bits</a><Opts> OptimizationBits(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"), + <a href="#cl::values">cl::values</a>( + clEnumVal(dce , "<i>Dead Code Elimination</i>"), + clEnumVal(constprop , "<i>Constant Propagation</i>"), + clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"), + clEnumVal(strip , "<i>Strip Symbols</i>"), + clEnumValEnd)); +</pre></div> + +<p>To test to see if <tt>constprop</tt> was specified, we can use the +<tt>cl:bits::isSet</tt> function:</p> + +<div class="doc_code"><pre> + if (OptimizationBits.isSet(constprop)) { + ... + } +</pre></div> + +<p>It's also possible to get the raw bit vector using the +<tt>cl::bits::getBits</tt> function:</p> + +<div class="doc_code"><pre> + unsigned bits = OptimizationBits.getBits(); +</pre></div> + +<p>Finally, if external storage is used, then the location specified must be of +<b>type</b> <tt>unsigned</tt>. In all other ways a <a +href="#bits"><tt>cl::bits</tt></a> option is equivalent to a <a +href="#list"> <tt>cl::list</tt></a> option.</p> + +</div> + + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="description">Adding freeform text to help output</a> +</div> + +<div class="doc_text"> + +<p>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 <tt>man</tt> page, providing concise information about +a program. Unix <tt>man</tt> 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 <a +href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> +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:</p> + +<div class="doc_code"><pre> +int main(int argc, char **argv) { + <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n" + " This program blah blah blah...\n"); + ... +} +</pre></div> + +<p>would yield the help output:</p> + +<div class="doc_code"><pre> +<b>OVERVIEW: CommandLine compiler example + + This program blah blah blah...</b> + +USAGE: compiler [options] <input file> + +OPTIONS: + ... + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename +</pre></div> + +</div> + + +<!-- *********************************************************************** --> +<div class="doc_section"> + <a name="referenceguide">Reference Guide</a> +</div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>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.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="positional">Positional Arguments</a> +</div> + +<div class="doc_text"> + +<p>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 <tt>grep</tt> +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:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><string> Regex (<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><regular expression></i>"), <a href="#cl::Required">cl::Required</a>); +<a href="#cl::opt">cl::opt</a><string> Filename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>")); +</pre></div> + +<p>Given these two option declarations, the <tt>-help</tt> output for our grep +replacement would look like this:</p> + +<div class="doc_code"><pre> +USAGE: spiffygrep [options] <b><regular expression> <input file></b> + +OPTIONS: + -help - display available options (-help-hidden for more) +</pre></div> + +<p>... and the resultant program could be used just like the standard +<tt>grep</tt> tool.</p> + +<p>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.</p> + +</div> + + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="--">Specifying positional options with hyphens</a> +</div> + +<div class="doc_text"> + +<p>Sometimes you may want to specify a value to your positional argument that +starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At +first, you will have trouble doing this, because it will try to find an argument +named '<tt>-foo</tt>', and will fail (and single quotes will not save you). +Note that the system <tt>grep</tt> has the same problem:</p> + +<div class="doc_code"><pre> + $ 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 . . . +</pre></div> + +<p>The solution for this problem is the same for both your tool and the system +version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on +the command line, it is telling the program that all options after the +'<tt>--</tt>' should be treated as positional arguments, not options. Thus, we +can use it like this:</p> + +<div class="doc_code"><pre> + $ spiffygrep -- -foo test.txt + ...output... +</pre></div> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="getPosition">Determining absolute position with getPosition()</a> +</div> +<div class="doc_text"> + <p>Sometimes an option can affect or modify the meaning of another option. For + example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells + <tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force + the file to be interpreted as if it contained source code in language + <tt>LANG</tt>. 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 + <tt>-llibname</tt> which is actually a positional argument that starts with + a dash.</p> + <p>So, generally, the problem is that you have two <tt>cl::list</tt> variables + that interact in some way. To ensure the correct interaction, you can use the + <tt>cl::list::getPosition(optnum)</tt> method. This method returns the + absolute position (as found on the command line) of the <tt>optnum</tt> + item in the <tt>cl::list</tt>.</p> + <p>The idiom for usage is like this:</p> + + <div class="doc_code"><pre> + static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); + static cl::list<std::string> Libraries("l", cl::ZeroOrMore); + + 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 + } + }</pre></div> + + <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an + <tt>unsigned getPosition()</tt> option that will provide the absolute position + of that option. You can apply the same approach as above with a + <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p> +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> 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.</p> + +<p>As a concrete example, lets say we are developing a replacement for the +standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first +you specify options to the shell itself (like <tt>-x</tt> 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:</p> + +<div class="doc_code"><pre> +<a href="#cl::opt">cl::opt</a><string> Script(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input script></i>"), <a href="#cl::init">cl::init</a>("-")); +<a href="#cl::list">cl::list</a><string> Argv(<a href="#cl::ConsumeAfter">cl::ConsumeAfter</a>, <a href="#cl::desc">cl::desc</a>("<i><program arguments>...</i>")); +<a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>")); +</pre></div> + +<p>which automatically provides the help output:</p> + +<div class="doc_code"><pre> +USAGE: spiffysh [options] <b><input script> <program arguments>...</b> + +OPTIONS: + -help - display available options (-help-hidden for more) + <b>-x - Enable trace output</b> +</pre></div> + +<p>At runtime, if we run our new shell replacement as `<tt>spiffysh -x test.sh +-a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the +<tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the +<tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they +were specified after the last positional argument (which is the script +name).</p> + +<p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can +be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified +per program, there must be at least one <a href="#positional">positional +argument</a> specified, there must not be any <a href="#cl::list">cl::list</a> +positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a +href="#cl::list">cl::list</a> option.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="storage">Internal vs External Storage</a> +</div> + +<div class="doc_text"> + +<p>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.</p> + +<p>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 +'<tt>-debug</tt>' 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 +<tt>CommandLine.h</tt>).</p> + +<p>To do this, set up your .h file with your option, like this for example:</p> + +<div class="doc_code"> +<pre> +<i>// 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. +//</i> +extern bool DebugFlag; + +<i>// 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.</i> +<span class="doc_hilite">#ifdef NDEBUG +#define DEBUG(X) +#else +#define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0) +<span class="doc_hilite">#endif</span> +</pre> +</div> + +<p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the +<tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to +set the <tt>DebugFlag</tt> 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 <a href="#cl::location">cl::location</a> +attribute:</p> + +<div class="doc_code"> +<pre> +bool DebugFlag; <i>// the actual value</i> +static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i> +Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>, <a href="#cl::location">cl::location</a>(DebugFlag)); +</pre> +</div> + +<p>In the above example, we specify "<tt>true</tt>" as the second argument to +the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the +template should not maintain a copy of the value itself. In addition to this, +we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so +that <tt>DebugFlag</tt> is automatically set.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="attributes">Option Attributes</a> +</div> + +<div class="doc_text"> + +<p>This section describes the basic attributes that you can specify on +options.</p> + +<ul> + +<li>The option name attribute (which is required for all options, except <a +href="#positional">positional options</a>) specifies what the option name is. +This option is specified in simple double quotes: + +<pre> +<a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>"); +</pre> + +</li> + +<li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a +description for the option to be shown in the <tt>-help</tt> output for the +program.</li> + +<li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute +specifies a string that can be used to fine tune the <tt>-help</tt> output for +a command line option. Look <a href="#value_desc_example">here</a> for an +example.</li> + +<li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an +initial value for a <a href="#cl::opt">scalar</a> 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. <b>Warning</b>: If you specify both +<b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option, +you must specify <b><tt>cl::location</tt></b> first, so that when the +command-line parser sees <b><tt>cl::init</tt></b>, 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.)</li> + +<li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where +to store the value for a parsed command line option if using external storage. +See the section on <a href="#storage">Internal vs External Storage</a> for more +information.</li> + +<li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute +specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is +an alias for.</li> + +<li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies +the string-to-value mapping to be used by the generic parser. It takes a +<b>clEnumValEnd terminated</b> list of (option, value, description) triplets +that +specify the option name, the value mapped to, and the description shown in the +<tt>-help</tt> for the tool. Because the generic parser is used most +frequently with enum values, two macros are often useful: + +<ol> + +<li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> 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.</li> + +<li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> 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.</li> + +</ol> + +You will get a compile time error if you try to use cl::values with a parser +that does not support it.</li> + +<li><a name="cl::multi_val">The <b><tt>cl::multi_val</tt></b></a> +attribute specifies that this option takes has multiple values +(example: <tt>-sectalign segname sectname sectvalue</tt>). This +attribute takes one unsigned argument - the number of values for the +option. This attribute is valid only on <tt>cl::list</tt> 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 <tt>cl::ValueDisallowed</tt>, +obviously).</li> + +</ul> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="modifiers">Option Modifiers</a> +</div> + +<div class="doc_text"> + +<p>Option modifiers are the flags and expressions that you pass into the +constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a +href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to +tweak how options are parsed and how <tt>-help</tt> output is generated to fit +your application well.</p> + +<p>These options fall into five main categories:</p> + +<ol> +<li><a href="#hiding">Hiding an option from <tt>-help</tt> output</a></li> +<li><a href="#numoccurrences">Controlling the number of occurrences + required and allowed</a></li> +<li><a href="#valrequired">Controlling whether or not a value must be + specified</a></li> +<li><a href="#formatting">Controlling other formatting options</a></li> +<li><a href="#misc">Miscellaneous option modifiers</a></li> +</ol> + +<p>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.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="hiding">Hiding an option from <tt>-help</tt> output</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and +<tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option +appears in the <tt>-help</tt> and <tt>-help-hidden</tt> output for the +compiled program:</p> + +<ul> + +<li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier +(which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a +href="#cl::list">cl::list</a></tt> options) indicates the option is to appear +in both help listings.</li> + +<li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the +default for <tt><a href="#cl::alias">cl::alias</a></tt> options) indicates that +the option should not appear in the <tt>-help</tt> output, but should appear in +the <tt>-help-hidden</tt> output.</li> + +<li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier +indicates that the option should not appear in any help output.</li> + +</ul> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="numoccurrences">Controlling the number of occurrences required and + allowed</a> +</div> + +<div class="doc_text"> + +<p>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.</p> + +<p>The allowed values for this option group are:</p> + +<ul> + +<li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which +is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a +href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will +allow either zero or one occurrence of the option to be specified.</li> + +<li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier +(which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class) +indicates that your program will allow the option to be specified zero or more +times.</li> + +<li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier +indicates that the specified option must be specified exactly one time.</li> + +<li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier +indicates that the option must be specified at least one time.</li> + +<li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a +href="#positional">Positional arguments section</a>.</li> + +</ul> + +<p>If an option is not specified, then the value of the option is equal to the +value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If +the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the +option value is initialized with the default constructor for the data type.</p> + +<p>If an option is specified multiple times for an option of the <tt><a +href="#cl::opt">cl::opt</a></tt> class, only the last value will be +retained.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="valrequired">Controlling whether or not a value must be specified</a> +</div> + +<div class="doc_text"> + +<p>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. '<tt>-index-depth=17</tt>') or as a trailing +string (e.g. '<tt>-o a.out</tt>').</p> + +<p>The allowed values for this option group are:</p> + +<ul> + +<li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier +(which is the default for <tt>bool</tt> 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 '<tt>-foo=true</tt>'. +If an option is specified with this mode, it is illegal for the value to be +provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To +get this behavior, you must use the <a +href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li> + +<li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier +(which is the default for all other types except for <a +href="#onealternative">unnamed alternatives using the generic parser</a>) +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 '<tt>-o +a.out</tt>' to work.</li> + +<li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a> +modifier (which is the default for <a href="#onealternative">unnamed +alternatives using the generic parser</a>) 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 '<tt>-foo=true</tt>').</li> + +</ul> + +<p>In general, the default values for this option group work just like you would +want them to. As mentioned above, you can specify the <a +href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean +argument to restrict your command line parser. These options are mostly useful +when <a href="#extensionguide">extending the library</a>.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="formatting">Controlling other formatting options</a> +</div> + +<div class="doc_text"> + +<p>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.</p> + +<ul> + +<li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a> +modifier (which is the default all options) specifies that this option is +"normal".</li> + +<li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier +specifies that this is a positional argument that does not have a command line +option associated with it. See the <a href="#positional">Positional +Arguments</a> section for more information.</li> + +<li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier +specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li> + +<li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> 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 <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a +linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the +'<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list) +options, that have the <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> +modifier added to allow the CommandLine library to recognize them. Note that +<b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> options must not have the +<b><tt><a href="#cl::ValueDisallowed">cl::ValueDisallowed</a></tt></b> modifier +specified.</li> + +<li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used +to implement Unix-style tools (like <tt>ls</tt>) that have lots of single letter +arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>' +command actually enables four different options, all of which are single +letters. Note that <b><tt><a href="#cl::Grouping">cl::Grouping</a></tt></b> +options cannot have values.</li> + +</ul> + +<p>The CommandLine library does not restrict how you use the <b><tt><a +href="#cl::Prefix">cl::Prefix</a></tt></b> or <b><tt><a +href="#cl::Grouping">cl::Grouping</a></tt></b> 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.</p> + +<p>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:</p> + +<div class="doc_code"><tt>parse(string OrigInput) {</tt> + +<ol> +<li><tt>string input = OrigInput;</tt> +<li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i> +<li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i> +<li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i> +<li><tt>if (getOption(input).isPrefix())<br> + return getOption(input).parse(input);</tt> +<li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br> + getOption(input).parse();<br> + OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br> + input = OrigInput;<br> + while (!isOption(input) && !input.empty()) input.pop_back();<br> +}</tt> +<li><tt>if (!OrigInput.empty()) error();</tt></li> +</ol> + +<p><tt>}</tt></p> +</div> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="misc">Miscellaneous option modifiers</a> +</div> + +<div class="doc_text"> + +<p>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.</p> + +<ul> + +<li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> 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 <tt>cl::CommaSeparated</tt> is specified: +"<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". 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 <a href="#cl::list">cl::list</a> option).</li> + +<li><a name="cl::PositionalEatsArgs">The +<b><tt>cl::PositionalEatsArgs</tt></b></a> 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, "<tt>pos1</tt>" and "<tt>pos2</tt>", the +string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar +-baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the +"<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li> + +<li><a name="cl::Sink">The <b><tt>cl::Sink</tt></b></a> modifier is +used to handle unknown options. If there is at least one option with +<tt>cl::Sink</tt> modifier specified, the parser passes +unrecognized option strings to it as values instead of signaling an +error. As with <tt>cl::CommaSeparated</tt>, this modifier +only makes sense with a <a href="#cl::list">cl::list</a> option.</li> + +</ul> + +<p>So far, these are the only three miscellaneous option modifiers.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="response">Response files</a> +</div> + +<div class="doc_text"> + +<p>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. Response files are enabled by an optional +fourth argument to +<a href="#cl::ParseEnvironmentOptions"><tt>cl::ParseEnvironmentOptions</tt></a> +and +<a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>. +</p> + +</div> + + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="toplevel">Top-Level Classes and Functions</a> +</div> + +<div class="doc_text"> + +<p>Despite all of the built-in flexibility, the CommandLine option library +really only consists of one function (<a +href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>) +and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a +href="#cl::list"><tt>cl::list</tt></a>, and <a +href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three +classes in detail.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt> + function</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called +directly from <tt>main</tt>, and is used to fill in the values of all of the +command line option variables once <tt>argc</tt> and <tt>argv</tt> are +available.</p> + +<p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters +(<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter +which holds <a href="#description">additional extra text</a> to emit when the +<tt>-help</tt> option is invoked, and a fourth boolean parameter that enables +<a href="#response">response files</a>.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt> + function</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects +as <a +href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>, +except that it is designed to take values for options from an environment +variable, for those cases in which reading the command line is not convenient or +desired. It fills in the values of all the command line option variables just +like <a +href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> +does.</p> + +<p>It takes four parameters: the name of the program (since <tt>argv</tt> may +not be available, it can't just look in <tt>argv[0]</tt>), the name of the +environment variable to examine, the optional +<a href="#description">additional extra text</a> to emit when the +<tt>-help</tt> option is invoked, and the boolean +switch that controls whether <a href="#response">response files</a> +should be read.</p> + +<p><tt>cl::ParseEnvironmentOptions</tt> will break the environment +variable's value up into words and then process them using +<a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>. +<b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support +quoting, so an environment variable containing <tt>-option "foo bar"</tt> will +be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>, +which is different from what you would get from the shell with the same +input.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt> + function</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::SetVersionPrinter</tt> function is designed to be called +directly from <tt>main</tt> and <i>before</i> +<tt>cl::ParseCommandLineOptions</tt>. Its use is optional. It simply arranges +for a function to be called in response to the <tt>--version</tt> option instead +of having the <tt>CommandLine</tt> 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 <tt>CommandLine</tt> facilities. Such programs should just define a small +function that takes no arguments and returns <tt>void</tt> and that prints out +whatever version information is appropriate for the program. Pass the address +of that function to <tt>cl::SetVersionPrinter</tt> to arrange for it to be +called when the <tt>--version</tt> option is given by the user.</p> + +</div> +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::opt">The <tt>cl::opt</tt> class</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::opt</tt> 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):</p> + +<div class="doc_code"><pre> +<b>namespace</b> cl { + <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>, + <b>class</b> ParserClass = parser<DataType> > + <b>class</b> opt; +} +</pre></div> + +<p>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 <a href="#storage">Internal +vs External Storage</a> for more information).</p> + +<p>The third template argument specifies which parser to use. The default value +selects an instantiation of the <tt>parser</tt> 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 <a +href="#customparser">custom parser</a>.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::list">The <tt>cl::list</tt> class</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::list</tt> 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:</p> + +<div class="doc_code"><pre> +<b>namespace</b> cl { + <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, + <b>class</b> ParserClass = parser<DataType> > + <b>class</b> list; +} +</pre></div> + +<p>This class works the exact same as the <a +href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is +the <b>type</b> of the external storage, not a boolean value. For this class, +the marker type '<tt>bool</tt>' is used to indicate that internal storage should +be used.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::bits">The <tt>cl::bits</tt> class</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::bits</tt> 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:</p> + +<div class="doc_code"><pre> +<b>namespace</b> cl { + <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, + <b>class</b> ParserClass = parser<DataType> > + <b>class</b> bits; +} +</pre></div> + +<p>This class works the exact same as the <a +href="#cl::opt"><tt>cl::lists</tt></a> class, except that the second argument +must be of <b>type</b> <tt>unsigned</tt> if external storage is used.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::alias">The <tt>cl::alias</tt> class</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form +aliases for other arguments.</p> + +<div class="doc_code"><pre> +<b>namespace</b> cl { + <b>class</b> alias; +} +</pre></div> + +<p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be +used to specify which option this is an alias for. Alias arguments default to +being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do +the conversion from string to data.</p> + +</div> + +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection"> + <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a> +</div> + +<div class="doc_text"> + +<p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra +help text to be printed out for the <tt>-help</tt> option.</p> + +<div class="doc_code"><pre> +<b>namespace</b> cl { + <b>struct</b> extrahelp; +} +</pre></div> + +<p>To use the extrahelp, simply construct one with a <tt>const char*</tt> +parameter to the constructor. The text passed to the constructor will be printed +at the bottom of the help message, verbatim. Note that multiple +<tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If +your tool needs to print additional help information, put all that help into a +single <tt>cl::extrahelp</tt> instance.</p> +<p>For example:</p> +<div class="doc_code"><pre> + cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); +</pre></div> +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="builtinparsers">Builtin parsers</a> +</div> + +<div class="doc_text"> + +<p>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 <tt>parser<type></tt> if the +command line option specifies that it uses values of type '<tt>type</tt>'. +Because of this, custom option processing is specified with specializations of +the '<tt>parser</tt>' class.</p> + +<p>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 <a href="#customparser">Writing a Custom Parser</a> for more +details on this type of library extension.</p> + +<ul> + +<li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a> +can be used to map strings values to any data type, through the use of the <a +href="#cl::values">cl::values</a> 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.</li> + +<li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a> +is used to convert boolean strings to a boolean value. Currently accepted +strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>", +"<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li> + +<li><a name="boolOrDefaultparser">The <b><tt>parser<boolOrDefault></tt> + specialization</b></a> 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 <b><tt>parser<bool></tt></b>.</li> + +<li><a name="stringparser">The <b><tt>parser<string></tt> +specialization</b></a> simply stores the parsed string into the string value +specified. No conversion or modification of the data is performed.</li> + +<li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a> +uses the C <tt>strtol</tt> 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 +'<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of +'<tt>0x</tt>' or '<tt>0X</tt>'.</li> + +<li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and +<b><tt>parser<float></tt> specializations</b> use the standard C +<tt>strtod</tt> function to convert floating point strings into floating point +values. As such, a broad range of string formats is supported, including +exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales. +</li> + +</ul> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"> + <a name="extensionguide">Extension Guide</a> +</div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>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.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="customparser">Writing a custom parser</a> +</div> + +<div class="doc_text"> + +<p>One of the simplest and most common extensions is the use of a custom parser. +As <a href="#builtinparsers">discussed previously</a>, 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.</p> + +<p>There are two ways to use a new parser:</p> + +<ol> + +<li> + +<p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for +your custom data type.<p> + +<p>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.</p> + +</li> + +<li> + +<p>Write an independent class, using it explicitly from options that need +it.</p> + +<p>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.</p> + +</li> + +</ol> + +<p>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 +'<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make +this the default for all <tt>unsigned</tt> options.</p> + +<p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p> + +<div class="doc_code"><pre> +<b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> { + <i>// parse - Return true on error.</i> + <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue, + <b>unsigned</b> &Val); +}; +</pre></div> + +<p>Our new class inherits from the <tt>cl::basic_parser</tt> 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 <tt>parse</tt> 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 '<tt>unsigned</tt>' variables.)</p> + +<p>For most purposes, the only method that must be implemented in a custom +parser is the <tt>parse</tt> method. The <tt>parse</tt> 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 '<tt>Val</tt>' to the parsed value. In +our example, we implement <tt>parse</tt> as:</p> + +<div class="doc_code"><pre> +<b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName, + <b>const</b> std::string &Arg, <b>unsigned</b> &Val) { + <b>const char</b> *ArgStart = Arg.c_str(); + <b>char</b> *End; + + <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i> + Val = (unsigned)strtol(ArgStart, &End, 0); + + <b>while</b> (1) { + <b>switch</b> (*End++) { + <b>case</b> 0: <b>return</b> false; <i>// No error</i> + <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i> + <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i> + <b>break</b>; + + <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>; + <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>; + <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>; + + default: + <i>// Print an error message if unrecognized character!</i> + <b>return</b> O.error("'" + Arg + "' value invalid for file size argument!"); + } + } +} +</pre></div> + +<p>This function implements a very simple parser for the kinds of strings we are +interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for +example), it is good enough for this example. Note that we use the option +itself to print out the error message (the <tt>error</tt> 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:</p> + +<div class="doc_code"><pre> +<b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser> +MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>), + <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>")); +</pre></div> + +<p>Which adds this to the output of our program:</p> + +<div class="doc_code"><pre> +OPTIONS: + -help - display available options (-help-hidden for more) + ... + <b>-max-file-size=<size> - Maximum file size to accept</b> +</pre></div> + +<p>And we can test that our parse works correctly now (the test program just +prints out the max-file-size argument value):</p> + +<div class="doc_code"><pre> +$ ./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! +</pre></div> + +<p>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.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="explotingexternal">Exploiting external storage</a> +</div> + +<div class="doc_text"> + <p>Several of the LLVM libraries define static <tt>cl::opt</tt> 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 <tt>llvm::DebugFlag</tt> exported by the + <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt> + flag exported by the <tt>lib/VMCore/Pass.cpp</tt> file.</p> + +<p>TODO: complete this section</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="dynamicopts">Dynamically adding command line options</a> +</div> + +<div class="doc_text"> + +<p>TODO: fill in this section</p> + +</div> + +<!-- *********************************************************************** --> + +<hr> +<address> + <a href="http://jigsaw.w3.org/css-validator/check/referer"><img + src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> + <a href="http://validator.w3.org/check/referer"><img + src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> + + <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> + <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br> + Last modified: $Date$ +</address> + +</body> +</html> |