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| author | Misha Brukman <brukman+llvm@gmail.com> | 2003-10-24 19:59:21 +0000 |
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| committer | Misha Brukman <brukman+llvm@gmail.com> | 2003-10-24 19:59:21 +0000 |
| commit | 9718e96228b6450fde37afba84546cf2a485f803 (patch) | |
| tree | 6a77e4f7ea58bf4f0e810a84306068e00ea14513 /docs/CommandLine.html | |
| parent | 02438ca2540a82f291ec0ce6a48d337a23d13b3e (diff) | |
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diff --git a/docs/CommandLine.html b/docs/CommandLine.html index a418dcba45..9b906c2af4 100644 --- a/docs/CommandLine.html +++ b/docs/CommandLine.html @@ -1,96 +1,112 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> -<html><head><title>CommandLine 2.0 Library Manual</title></head> -<body bgcolor=white> - -<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0> -<tr><td> <font size=+3 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>CommandLine 2.0 Library Manual</b></font></td> -</tr></table> +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <link rel="stylesheet" href="llvm.css" type="text/css"> + <title>CommandLine 2.0 Library Manual</title> +</head> +<body> + +<div class="doc_title"> + CommandLine 2.0 Library Manual +</div> <ol> - <li><a href="#introduction">Introduction</a> + <li><a href="#introduction">Introduction</a></li> + <li><a href="#quickstart">Quick Start Guide</a> <ol> - <li><a href="#bool">Boolean Arguments</a> - <li><a href="#alias">Argument Aliases</a> + <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><a href="#namedalternatives">Named alternatives</a> - <li><a href="#list">Parsing a list of options</a> - <li><a href="#description">Adding freeform text to help output</a> - </ol> + 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="#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><a href="#--">Specifying positional options with hyphens</a></li> <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> - modifier</a> - </ul> - <li><a href="#storage">Internal vs External Storage</a> - <li><a href="#attributes">Option Attributes</a> + 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><a href="#numoccurances">Controlling the number of occurances - required and allowed</a> + <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><a href="#formatting">Controlling other formatting options</a> - <li><a href="#misc">Miscellaneous option modifiers</a> - </ul> + specified</a></li> + <li><a href="#formatting">Controlling other formatting options</a></li> + <li><a href="#misc">Miscellaneous option modifiers</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><a href="#cl::ParseEnvironmentOptions">The - <tt>cl::ParseEnvironmentOptions</tt> function</a> - <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a> - <li><a href="#cl::list">The <tt>cl::list</tt> class</a> - <li><a href="#cl::alias">The <tt>cl::alias</tt> class</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::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::alias">The <tt>cl::alias</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> + parser</a></li> <li><a href="#boolparser">The <tt>parser<bool></tt> - specialization</a> + specialization</a></li> <li><a href="#stringparser">The <tt>parser<string></tt> - specialization</a> + specialization</a></li> <li><a href="#intparser">The <tt>parser<int></tt> - specialization</a> + specialization</a></li> <li><a href="#doubleparser">The <tt>parser<double></tt> and - <tt>parser<float></tt> specializations</a> - </ul> - </ol> + <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><a href="#explotingexternal">Exploiting external storage</a> - <li><a href="#dynamicopts">Dynamically adding command line options</a> - </ol> - - <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p> -</ol><p> + <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_text"> + <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b></p> +</div> <!-- *********************************************************************** --> -<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0> -<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b> -<a name="introduction">Introduction -</b></font></td></tr></table><ul> +<div class="doc_section"> + Introduction +</div> <!-- *********************************************************************** --> -This document describes the CommandLine argument processing library. It will +<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> +changed</a>).</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> +<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 @@ -98,43 +114,45 @@ 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).<p> +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.<p> +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.<p> +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.<p> +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.<p> +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...<p> +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.<p> +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.<p> +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 @@ -142,49 +160,52 @@ 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>.<p> +href="#cl::ConsumeAfter">interpreter style options</a>.</li> </ol> -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> - +<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> <!-- *********************************************************************** --> -</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b> -<a name="quickstart">Quick Start Guide -</b></font></td></tr></table><ul> +<div class="doc_section"> + <a name="quickstart">Quick Start Guide</a> +</div> <!-- *********************************************************************** --> -This section of the manual runs through a simple CommandLine'ification of a +<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> +can do.</p> -To start out, you need to include the CommandLine header file into your -program:<p> +<p>To start out, you need to include the CommandLine header file into your +program:</p> <pre> #include "Support/CommandLine.h" -</pre><p> +</pre> -Additionally, you need to add this as the first line of your main program:<p> +<p>Additionally, you need to add this as the first line of your main +program:</p> <pre> int main(int argc, char **argv) { <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv); ... } -</pre><p> +</pre> -... which actually parses the arguments and fills in the variable -declarations.<p> +<p>... which actually parses the arguments and fills in the variable +declarations.</p> -Now that you are ready to support command line arguments, we need to tell the +<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 argument 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 @@ -192,22 +213,23 @@ 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> +represented like this:</p> -<pre><a name="value_desc_example"> -<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><p> +<p><tt> +<a name="value_desc_example"> +<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>"));</a> +</tt></p> -This declares a global variable "<tt>OutputFilename</tt>" that is used to +<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> +that the data type that we are parsing is a string.</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> +<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> <pre> USAGE: compiler [options] @@ -217,40 +239,39 @@ OPTIONS: <b>-o <filename> - Specify output filename</b> </pre> -Because we specified that the command line option should parse using the +<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> +example:</p> <pre> ... ofstream Output(OutputFilename.c_str()); if (Out.good()) ... ... -</pre><p> +</pre> -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 +<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> +discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p> - -Continuing the example, we would like to have our compiler take an input +<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> +in option form. We use this feature like this:</p> <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> -This declaration indicates that the first positional argument should be treated -as the input filename. Here we use the <tt><a +<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 @@ -258,26 +279,26 @@ 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> +<tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p> <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> -Again, the CommandLine library does not require the options to be specified in -any particular order, so the above declaration is equivalent to:<p> +<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> <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> -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 +<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> +extended to:</p> <pre> USAGE: compiler [options] <b><input file></b> @@ -287,42 +308,44 @@ OPTIONS: -o <filename> - Specify output filename </pre> -... indicating that an input filename is expected.<p> - +<p>... indicating that an input filename is expected.</p> +</div> <!-- ======================================================================= --> -</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b> -<a name="bool">Boolean Arguments -</b></font></td></tr></table><ul> +<div class="doc_subsection"> + <a name="bool">Boolean Arguments</a> +</div> -In addition to input and output filenames, we would like the compiler example to -support three boolean flags: "<tt>-f</tt>" to force overwriting of the output +<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 overwriting of the output file, "<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> +of boolean type like this:</p> <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::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><p> +</pre> -This does what you would expect: it declares three boolean variables +<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> +shown in the "<tt>--help-hidden</tt>" output).</p> -The CommandLine library uses a <a href="#builtinparsers">different parser</a> +<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> +following inputs:</p> <pre> compiler -f # No value, 'Force' == true @@ -331,14 +354,14 @@ following inputs:<p> compiler -f=FALSE # Value specified, 'Force' == false </pre> -... 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 +<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> +library calls to parse the string value into the specified data type.</p> -With the declarations above, "<tt>compiler --help</tt>" emits this:<p> +<p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p> <pre> USAGE: compiler [options] <input file> @@ -348,9 +371,9 @@ OPTIONS: -o - Override output filename <b>-quiet - Don't print informational messages</b> -help - display available options (--help-hidden for more) -</pre><p> +</pre> -and "<tt>opt --help-hidden</tt>" prints this:<p> +<p>and "<tt>opt --help-hidden</tt>" prints this:</p> <pre> USAGE: compiler [options] <input file> @@ -361,96 +384,103 @@ OPTIONS: <b>-q - Don't print informational messages</b> -quiet - Don't print informational messages -help - display available options (--help-hidden for more) -</pre><p> +</pre> -This brief example has shown you how to use the '<tt><a +<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> +and <a href="#list">lists</a> of options.</p> +</div> <!-- ======================================================================= --> -</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b> -<a name="alias">Argument Aliases -</b></font></td></tr></table><ul> +<div class="doc_subsection"> + <a name="alias">Argument Aliases</a> +</div> + +<div class="doc_text"> -So far, the example works well, except for the fact that we need to check the -quiet condition like this now:<p> +<p>So far, the example works well, except for the fact that we need to check the +quiet condition like this now:</p> <pre> ... if (!Quiet && !Quiet2) printInformationalMessage(...); ... -</pre><p> +</pre> -... which is a real pain! Instead of defining two values for the same +<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> +a value itself:</p> <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><p> +</pre> -The third line (which is the only one we modified from above) defines a +<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> +output</tt>).</p> -Now the application code can simply use:<p> +<p>Now the application code can simply use:</p> <pre> ... if (!Quiet) printInformationalMessage(...); ... -</pre><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> +</pre> +<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> <!-- ======================================================================= --> -</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b> -<a name="onealternative">Selecting an alternative from a set of possibilities -</b></font></td></tr></table><ul> +<div class="doc_subsection"> + <a name="onealternative">Selecting an alternative from a set of + possibilities</a> +</div> + +<div class="doc_text"> -So far, we have seen how the CommandLine library handles builtin types like +<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> +things it doesn't know about, like enums or '<tt>int*</tt>'s?</p> -The answer is that it uses a table driven generic parser (unless you specify +<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, are -requires you to tell it what this mapping should be.<p> +requires you to tell it what this mapping should be.</p> -Lets say that we would like to add four optimizations 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> +<p>Lets say that we would like to add four optimizations 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>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this -erroneous input for us. +erroneous input for us.</li> -<li>We would have to test 4 different variables to see which ones are set. +<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. +see if some level >= "<tt>-O1</tt>" is enabled.</li> -</ol><p> +</ol> -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> +<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> <pre> enum OptLevel { @@ -468,16 +498,16 @@ enum OptLevel { ... if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); ... -</pre><p> +</pre> -This declaration defines a variable "<tt>OptimizationLevel</tt>" of the +<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>0</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> +help output now is:</p> <pre> USAGE: compiler [options] <input file> @@ -494,10 +524,10 @@ OPTIONS: -quiet - Don't print informational messages </pre> -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> +<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> <pre> enum OptLevel { @@ -515,28 +545,30 @@ enum OptLevel { ... if (OptimizationLevel == Debug) outputDebugInfo(...); ... -</pre><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> +</pre> +<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> <!-- ======================================================================= --> -</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b> -<a name="namedalternatives">Named Alternatives -</b></font></td></tr></table><ul> +<div class="doc_subsection"> + <a name="namedalternatives">Named Alternatives</a> +</div> -Another useful argument form is a named alternative style. We shall use this +<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> |