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Using TCLAP to parse command line
2015-12-29 10:44:55 +00:00
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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Templatized C++ Command Line Parser Manual</title><link rel="stylesheet" href="style.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.71.1" /></head><body><div class="book" lang="en" xml:lang="en"><div class="titlepage"><div><div><h1 class="title"><a id="id400620"></a>Templatized C++ Command Line Parser Manual</h1></div><div><div class="author"><h3 class="author"><span class="firstname">Michael</span> <span class="othername">E</span> <span class="surname">Smoot</span></h3></div></div><div><p class="copyright">Copyright © 2003,2004,2005,2006,2009,2011 Michael E. Smoot</p></div></div><hr /></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#BASIC_USAGE">1. Basic Usage</a></span></dt><dd><dl><dt><span class="sect1"><a href="#OVERVIEW">Overview</a></span></dt><dt><span class="sect1"><a href="#EXAMPLE">Example</a></span></dt><dd><dl><dt><span class="sect2"><a href="#LIBRARY_PROPERTIES">Library Properties</a></span></dt><dt><span class="sect2"><a href="#ARG_PROPERTIES">Common Argument Properties</a></span></dt></dl></dd><dt><span class="sect1"><a href="#COMPILING">Compiling</a></span></dt></dl></dd><dt><span class="chapter"><a href="#FUNDAMENTAL_CLASSES">2. Fundamental Classes</a></span></dt><dd><dl><dt><span class="sect1"><a href="#COMMAND_LINE"><code class="classname">CmdLine</code></a></span></dt><dt><span class="sect1"><a href="#SWITCH_ARG"><code class="classname">SwitchArg</code></a></span></dt><dt><span class="sect1"><a href="#VALUE_ARG"><code class="classname">ValueArg</code></a></span></dt><dt><span class="sect1"><a href="#MULTI_ARG"><code class="classname">MultiArg</code></a></span></dt><dt><span class="sect1"><a href="#MULTI_SWITCH_ARG"><code class="classname">MultiSwitchArg</code></a></span></dt><dt><span class="sect1"><a href="#UNLABELED_VALUE_ARG"><code class="classname">UnlabeledValueArg</code></a></span></dt><dt><span class="sect1"><a href="#UNLABELED_MULTI_ARG"><code class="classname">UnlabeledMultiArg</code></a></span></dt></dl></dd><dt><span class="chapter"><a href="#COMPLICATIONS">3. Complications</a></span></dt><dd><dl><dt><span class="sect1"><a href="#COMBINE_SWITCHES">I want to combine multiple switches into one argument...</a></span></dt><dt><span class="sect1"><a href="#XOR">I want one argument or the other, but not both...</a></span></dt><dt><span class="sect1"><a href="#NO_FLAG">I have more arguments than single flags make sense for...</a></span></dt><dt><span class="sect1"><a href="#CONSTRAINT">I want to constrain the values allowed for a particular
argument...</a></span></dt><dt><span class="sect1"><a href="#ARG_ADD_CMDLINE">I want the Args to add themselves to the CmdLine...</a></span></dt><dt><span class="sect1"><a href="#CHANGE_OUTPUT">I want different output than what is provided...</a></span></dt><dt><span class="sect1"><a href="#NO_HELP_VERSION">I don't want the --help and --version switches to be created automatically...</a></span></dt><dt><span class="sect1"><a href="#IGNORE_ARGS">I want to ignore certain arguments...</a></span></dt><dt><span class="sect1"><a href="#READING_HEX_INTEGERS">I want to read hex integers as arguments...</a></span></dt><dt><span class="sect1"><a href="#USING_ARGTRAITS">I want to use different types...</a></span></dt><dt><span class="sect1"><a href="#CHANGING_STARTSTRINGS">I want to use Windows-style flags like "/x" and "/y"...</a></span></dt></dl></dd><dt><span class="chapter"><a href="#NOTES">4. Notes</a></span></dt><dd><dl><dt><span class="sect1"><a href="#DESCRIPTION_EXCEPTIONS">Type Descriptions</a></span></dt><dt><span class="sect1"><a href="#VISITORS">Visitors</a></span></dt><dt><span class="sect1"><a href="#MORE_INFO">More Information</a></span></dt></dl></dd></dl></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="BASIC_USAGE"></a>Chapter 1. Basic Usage</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#OVERVIEW">Overview</a></span></dt><dt><span class="sect1"><a href="#EXAMPLE">Example</a></span></dt><dd><dl><dt><span class="sect2"><a href="#LIBRARY_PROPERTIES">Library Properties</a></span></dt><dt><span class="sect2"><a href="#ARG_PROPERTIES">Common Argument Properties</a></span></dt></dl></dd><dt><span class="sect1"><a href="#COMPILING">Compiling</a></span></dt></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="OVERVIEW"></a>Overview</h2></div></div></div><p>
<span class="emphasis"><em>TCLAP</em></span> has a few key classes to be aware of.
The first is the
<code class="classname">CmdLine</code> (command line) class. This class parses
the command line passed to it according to the arguments that it
contains. Arguments are separate objects that are added to the
<code class="classname">CmdLine</code> object one at a time. The six
argument classes are: <code class="classname">ValueArg</code>,
<code class="classname">UnlabeledValueArg</code>,
<code class="classname">SwitchArg</code>, <code class="classname">MultiSwitchArg</code>,
<code class="classname">MultiArg</code> and
<code class="classname">UnlabeledMultiArg</code>.
These classes are templatized, which means they can be defined to parse
a value of any <a href="#USING_ARGTRAITS" title="I want to use different types..."> type</a>. Once you add the
arguments to the <code class="classname">CmdLine</code> object, it parses the
command line
and assigns the data it finds to the specific argument objects it
contains. Your program accesses the values parsed by
calls to the <code class="methodname">getValue()</code> methods of the
argument objects.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="EXAMPLE"></a>Example</h2></div></div></div><p>
Here is a simple <a href="test1.cpp" target="_top"> example</a> ...
</p><pre class="programlisting">
#include &lt;string&gt;
#include &lt;iostream&gt;
#include &lt;algorithm&gt;
#include &lt;tclap/CmdLine.h&gt;
int main(int argc, char** argv)
{
// Wrap everything in a try block. Do this every time,
// because exceptions will be thrown for problems.
try {
// Define the command line object, and insert a message
// that describes the program. The "Command description message"
// is printed last in the help text. The second argument is the
// delimiter (usually space) and the last one is the version number.
// The CmdLine object parses the argv array based on the Arg objects
// that it contains.
TCLAP::CmdLine cmd("Command description message", ' ', "0.9");
// Define a value argument and add it to the command line.
// A value arg defines a flag and a type of value that it expects,
// such as "-n Bishop".
TCLAP::ValueArg&lt;std::string&gt; nameArg("n","name","Name to print",true,"homer","string");
// Add the argument nameArg to the CmdLine object. The CmdLine object
// uses this Arg to parse the command line.
cmd.add( nameArg );
// Define a switch and add it to the command line.
// A switch arg is a boolean argument and only defines a flag that
// indicates true or false. In this example the SwitchArg adds itself
// to the CmdLine object as part of the constructor. This eliminates
// the need to call the cmd.add() method. All args have support in
// their constructors to add themselves directly to the CmdLine object.
// It doesn't matter which idiom you choose, they accomplish the same thing.
TCLAP::SwitchArg reverseSwitch("r","reverse","Print name backwards", cmd, false);
// Parse the argv array.
cmd.parse( argc, argv );
// Get the value parsed by each arg.
std::string name = nameArg.getValue();
bool reverseName = reverseSwitch.getValue();
// Do what you intend.
if ( reverseName )
{
std::reverse(name.begin(),name.end());
std::cout &lt;&lt; "My name (spelled backwards) is: " &lt;&lt; name &lt;&lt; std::endl;
}
else
std::cout &lt;&lt; "My name is: " &lt;&lt; name &lt;&lt; std::endl;
} catch (TCLAP::ArgException &amp;e) // catch any exceptions
{ std::cerr &lt;&lt; "error: " &lt;&lt; e.error() &lt;&lt; " for arg " &lt;&lt; e.argId() &lt;&lt; std::endl; }
}
</pre><p>
The output should look like:
</p><pre class="programlisting">
% test1 -n mike
My name is: mike
% test1 -n mike -r
My name (spelled backwards) is: ekim
% test1 -r -n mike
My name (spelled backwards) is: ekim
% test1 -r
PARSE ERROR:
One or more required arguments missing!
Brief USAGE:
test1 [-r] -n &lt;string&gt; [--] [-v] [-h]
For complete USAGE and HELP type:
test1 --help
% test1 --help
USAGE:
test1 [-r] -n &lt;string&gt; [--] [-v] [-h]
Where:
-r, --reverse
Print name backwards
-n &lt;string&gt; --name &lt;string&gt;
(required) (value required) Name to print
--, --ignore_rest
Ignores the rest of the labeled arguments following this flag.
-v, --version
Displays version information and exits.
-h, --help
Displays usage information and exits.
Command description message
</pre><p>
</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="LIBRARY_PROPERTIES"></a>Library Properties</h3></div></div></div><p>
This example shows a number of different properties of the
library...
</p><div class="itemizedlist"><ul type="disc"><li>Arguments can appear in any order (...mostly,
<a href="#COMPLICATIONS" title="Chapter 3. Complications"> more</a> on this later).</li><li>The <em class="parameter"><code>help</code></em>, <em class="parameter"><code>version</code></em>
and <em class="parameter"><code>--</code></em><code class="classname">SwitchArg</code>s
are specified automatically. Using either the <em class="parameter"><code>-h</code></em> or
<em class="parameter"><code>--help</code></em> flag will cause the USAGE message to be displayed,
<em class="parameter"><code>-v</code></em> or <em class="parameter"><code>--version</code></em> will cause
any version information to
be displayed, and <em class="parameter"><code>--</code></em> or
<em class="parameter"><code>--ignore_rest</code></em> will cause the
remaining labeled arguments to be ignored. These switches are
included by default on every command line. You can <a href="#">disable this functionality</a> if desired (although we don't recommend it).
How we generate the behavior behind these flags is described
<a href="#VISITORS" title="Visitors"> later</a>.
</li><li>If there is an error parsing the command line (e.g. a required
argument isn't provided), the program exits and displays a brief
USAGE and an error message.</li><li>The program name is assumed to always be argv[0], so it isn't
specified directly.</li><li>A value delimiter character can be specified. This means that if you
prefer arguments of the style <em class="parameter"><code>-s=asdf</code></em> instead of
<em class="parameter"><code>-s asdf</code></em>, you can do so.</li><li><span class="emphasis"><em>Always wrap everything in a try block that catches
ArgExceptions!</em></span> Any problems found in constructing the
<code class="classname">CmdLine</code>, constructing the <code class="classname">Arg</code>s,
or parsing the command line will throw an
<code class="classname">ArgException</code>.</li></ul></div><p>
</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="ARG_PROPERTIES"></a>Common Argument Properties</h3></div></div></div><p>
Arguments, whatever their type, have a few common properties.
These properties are set in the constructors of the arguments.
</p><div class="itemizedlist"><ul type="disc"><li>First is the flag or the character preceded by a dash(-) that
signals the beginning of the argument on the command line.</li><li>Arguments also have names, which can also be used
as an alternative flag on the command line, this time preceded by two dashes
(--) [like the familiar <code class="function">getopt_long()</code>].</li><li>Next is the description of the argument. This is a short
description of the argument displayed in the help/usage message
when needed.</li><li>The following parameters in the constructors vary depending on
the type of argument. Some possible values include:
<div class="itemizedlist"><ul type="circle"><li>A boolean value indicating whether the Arg is required or not. </li><li>A default value.</li><li>A <a href="#DESCRIPTION_EXCEPTIONS" title="Type Descriptions">description</a> of the type of value expected.</li><li>A <a href="#CONSTRAINT" title="I want to constrain the values allowed for a particular argument...">constraint</a> on the value expected.</li><li>The CmdLine instance that the Arg should be added to.</li><li>A <a href="#VISITORS" title="Visitors">Visitor</a>.</li></ul></div></li><li>See the <a href="html/index.html" target="_top">API Documentation</a> for more detail.</li></ul></div><p>
</p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="COMPILING"></a>Compiling</h2></div></div></div><p>
<span class="emphasis"><em>TCLAP</em></span> is implemented entirely in header files
which means you only need to include CmdLine.h to use the library.
</p><pre class="programlisting">
#include &lt;tclap/CmdLine.h&gt;
</pre><p>
You'll need to make sure that your compiler can see the header
files. If you do the usual "make install" then your compiler should
see the files by default. Alternatively, you can use the -I
complier argument to specify the exact location of the libraries.
</p><pre class="programlisting">
c++ -o my_program -I /some/place/tclap-1.X/include my_program.cpp
</pre><p>
Where /some/place/tclap-1.X is the place you have unpacked the
distribution.
</p><p>
Finally, if you want to include <span class="emphasis"><em>TCLAP</em></span> as part of
your software
(which is perfectly OK, even encouraged) then simply copy the
contents of /some/place/tclap-1.X/include (the tclap directory and
all of the header files it contains) into your include
directory. The necessary m4 macros for proper configuration are included
in the config directory.
</p><p>
<span class="emphasis"><em>TCLAP</em></span> was developed on Linux and MacOSX systems.
It is also known
to work on Windows, Sun and Alpha platforms. We've made every
effort to keep the library compliant with the ANSI C++ standard so
if your compiler meets the standard, then this library should work
for you. Please let us know if this is not the case!
</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="WINDOWS_NOTE"></a>Windows Note</h3></div></div></div><p>
As we understand things, Visual C++ does not have the file
<code class="filename">config.h</code> which is used to make platform
specific definitions. In this situation, we assume that you
have access to <code class="classname">sstream</code>. Our understanding is that
this should not be a problem for VC++ 7.x. However, if this
is not the case and you need to use <code class="classname">strstream</code>,
then simply tell your compiler to define the variable
<code class="constant">HAVE_STRSTREAM</code> and undefine
<code class="constant">HAVE_SSTREAM</code> That
<span class="emphasis"><em>should</em></span> work. We think. Alternatively, just edit
the files <code class="filename">ValueArg.h</code> and <code class="filename">MultiArg.h</code>.
</p></div><p>
</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="RANDOM_NOTE"></a>Random Note</h3></div></div></div><p>
If your compiler doesn't support the <code class="methodname">using</code> syntax used
in <code class="classname">UnlabeledValueArg</code> and
<code class="classname">UnlabeledMultiArg</code> to support two stage name lookup,
then you have two options. Either comment out the statements if you don't
need two stage name lookup, or do a bunch of search and replace and use
the <code class="methodname">this</code> pointer syntax: e.g.
<code class="methodname">this-&gt;_ignoreable</code> instead
of just <code class="methodname">_ignorable</code> (do this for each variable
or method referenced by <code class="methodname">using</code>).
</p></div><p>
</p></div></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="FUNDAMENTAL_CLASSES"></a>Chapter 2. Fundamental Classes</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#COMMAND_LINE"><code class="classname">CmdLine</code></a></span></dt><dt><span class="sect1"><a href="#SWITCH_ARG"><code class="classname">SwitchArg</code></a></span></dt><dt><span class="sect1"><a href="#VALUE_ARG"><code class="classname">ValueArg</code></a></span></dt><dt><span class="sect1"><a href="#MULTI_ARG"><code class="classname">MultiArg</code></a></span></dt><dt><span class="sect1"><a href="#MULTI_SWITCH_ARG"><code class="classname">MultiSwitchArg</code></a></span></dt><dt><span class="sect1"><a href="#UNLABELED_VALUE_ARG"><code class="classname">UnlabeledValueArg</code></a></span></dt><dt><span class="sect1"><a href="#UNLABELED_MULTI_ARG"><code class="classname">UnlabeledMultiArg</code></a></span></dt></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="COMMAND_LINE"></a><code class="classname">CmdLine</code></h2></div></div></div><p>
The <code class="classname">CmdLine</code> class contains the arguments that define
the command line and manages the parsing of the command line. The
<code class="classname">CmdLine</code> doesn't parse the command line itself it only
manages the parsing. The actual parsing of individual arguments occurs within
the arguments themselves. The <code class="classname">CmdLine</code> keeps track of
of the required arguments, <a href="#XOR" title="I want one argument or the other, but not both...">relationships</a>
between arguments, and <a href="#CHANGE_OUTPUT" title="I want different output than what is provided...">output</a> generation.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="SWITCH_ARG"></a><code class="classname">SwitchArg</code></h2></div></div></div><p><code class="classname">SwitchArg</code>s are what the name implies:
simple, on/off, boolean switches. Use <code class="classname">SwitchArg</code>s
anytime you want to turn
some sort of system property on or off. <code class="classname">SwitchArg</code>s
don't parse a value. They return <code class="constant">TRUE</code> or
<code class="constant">FALSE</code>, depending on whether the switch has been found
on the command line and what the default value was defined as.</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="VALUE_ARG"></a><code class="classname">ValueArg</code></h2></div></div></div><p><code class="classname">ValueArg</code>s are arguments that read a
value of some type
from the command line. Any time you need a file name, a number,
etc. use a <code class="classname">ValueArg</code> or one of its variants.
All <code class="classname">ValueArg</code>s are
<a href="#USING_ARGTRAITS" title="I want to use different types..."> templatized</a> and will attempt to parse
the string its flag matches on the command line as the type it is
specified as. <code class="classname">ValueArg&lt;int&gt;</code>
will attempt to parse an
int, <code class="classname">ValueArg&lt;float&gt;</code> will attempt to
parse a float, etc. If <code class="methodname">operator&gt;&gt;</code>
for the specified type doesn't
recognize the string on the command line as its defined type, then
an exception will be thrown.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="MULTI_ARG"></a><code class="classname">MultiArg</code></h2></div></div></div><p>
A <code class="classname">MultiArg</code> is a <code class="classname">ValueArg</code> that
can be specified more than once on a command line and instead of returning
a single value, returns a <code class="classname">vector</code> of values.
</p><p>
Imagine a compiler that allows you to specify multiple directories
to search for libraries...
</p><pre class="programlisting">
% fooCompiler -L /dir/num1 -L /dir/num2 file.foo
</pre><p>
Exceptions will occur if you try to do this
with a <code class="classname">ValueArg</code> or a <code class="classname">SwitchArg</code>.
In situations like this, you will want to use a
<code class="classname">MultiArg</code>. A
<code class="classname">MultiArg</code> is essentially a
<code class="classname">ValueArg</code> that appends any
value that it matches and parses onto a vector of values. When the
<code class="methodname">getValue()</code> method is called, a vector of
values, instead of a single value is returned. A
<code class="classname">MultiArg</code> is declared much like
a <code class="classname">ValueArg</code>:
</p><pre class="programlisting">
MultiArg&lt;int&gt; itest("i", "intTest", "multi int test", false,"int" );
cmd.add( itest );
</pre><p>
Note that <code class="classname">MultiArg</code>s can be added to the
<code class="classname">CmdLine</code> in any order (unlike
<a href="#UNLABELED_MULTI_ARG" title="UnlabeledMultiArg"> UnlabeledMultiArg</a>).
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="MULTI_SWITCH_ARG"></a><code class="classname">MultiSwitchArg</code></h2></div></div></div><p>
A <code class="classname">MultiSwitchArg</code> is a <code class="classname">SwitchArg</code>
that can be specified more than once on a command line.
This can be useful
when command lines are constructed automatically from within other applications
or when a switch occurring
more than once indicates a value (-V means a little verbose -V -V -V means a lot
verbose), You can use a <code class="classname">MultiSwitchArg</code>.
The call
to <code class="methodname">getValue()</code> for a <code class="classname">MultiSwitchArg</code> returns the number (int) of times
the switch has been found on the command line in addition to the default value.
Here is an example using the default initial value of 0:
</p><pre class="programlisting">
MultiSwitchArg quiet("q","quiet","Reduce the volume of output");
cmd.add( quiet );
</pre><p>
Alternatively, you can specify your own initial value:
</p><pre class="programlisting">
MultiSwitchArg quiet("q","quiet","Reduce the volume of output",5);
cmd.add( quiet );
</pre><p>
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="UNLABELED_VALUE_ARG"></a><code class="classname">UnlabeledValueArg</code></h2></div></div></div><p>
An <code class="classname">UnlabeledValueArg</code> is a <code class="classname">ValueArg</code> that is not identified by a flag on the command line. Instead
<code class="classname">UnlabeledValueArg</code>s are identified by their position in
the argv array.
</p><p>
To this point all of our arguments have had labels (flags)
identifying them on the command line, but there are some
situations where flags are burdensome and not worth the effort. One
example might be if you want to implement a magical command we'll
call <span><strong class="command">copy</strong></span>. All <span><strong class="command">copy</strong></span> does is
copy the file specified
in the first argument to the file specified in the second argument.
We can do this using <code class="classname">UnlabeledValueArg</code>s which are pretty
much just <code class="classname">ValueArg</code>s without the flag specified,
which tells
the <code class="classname">CmdLine</code> object to treat them accordingly.
The code would look like this:
</p><pre class="programlisting">
UnlabeledValueArg&lt;float&gt; nolabel( "name", "unlabeled test", 3.14,
"nameString" );
cmd.add( nolabel );
</pre><p>
Everything else is handled identically to what is seen above. The
only difference to be aware of, and this is important: <span class="emphasis"><em>the order
that UnlabeledValueArgs are added to the <code class="classname">CmdLine</code>
is the order that they will be parsed!!!!</em></span>
This is <span class="emphasis"><em>not</em></span> the case for normal
<code class="classname">SwitchArg</code>s and <code class="classname">ValueArg</code>s.
What happens internally is the first argument that the
<code class="classname">CmdLine</code> doesn't recognize is assumed to be
the first <code class="classname">UnlabeledValueArg</code> and
parses it as such. Note that you are allowed to intersperse labeled
args (SwitchArgs and ValueArgs) in between
<code class="classname">UnlabeledValueArgs</code> (either on the command line
or in the declaration), but the <code class="classname">UnlabeledValueArgs</code>
will still be parsed in the order they are added. Just remember that order is
important for unlabeled arguments.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="UNLABELED_MULTI_ARG"></a><code class="classname">UnlabeledMultiArg</code></h2></div></div></div><p>
An <code class="classname">UnlabeledMultiArg</code> is an <code class="classname">UnlabeledValueArg</code> that allows more than one value to be specified. Only one
<code class="classname">UnlabeledMultiArg</code> can be specified per command line.
The <code class="classname">UnlabeledMultiArg</code> simply reads the remaining
values from argv up until -- or the end of the array is reached.
</p><p>
Say you want a strange command
that searches each file specified for a given string (let's call it
<span><strong class="command">grep</strong></span>), but you don't want to have to type in all of the file
names or write a script to do it for you. Say,
</p><pre class="programlisting">
% grep pattern *.txt
</pre><p>
First remember that the <span class="emphasis"><em>*</em></span> is handled by the shell and
expanded accordingly, so what the program <span><strong class="command">grep</strong></span> sees is
really something like:
</p><pre class="programlisting">
% grep pattern file1.txt file2.txt fileZ.txt
</pre><p>
To handle situations where multiple, unlabeled arguments are needed,
we provide the <code class="classname">UnlabeledMultiArg</code>.
<code class="classname">UnlabeledMultiArg</code>s
are declared much like everything else, but with only a description
of the arguments. By default, if an <code class="classname">UnlabeledMultiArg</code>
is specified, then at least one is required to be present or an
exception will be thrown. The most important thing to remember is,
that like <code class="classname">UnlabeledValueArg</code>s: order matters!
In fact, <span class="emphasis"><em>an UnlabeledMultiArg must be the last argument added to the
CmdLine!</em></span>. Here is what a declaration looks like:
</p><pre class="programlisting">
//
// UnlabeledMultiArg must be the LAST argument added!
//
UnlabeledMultiArg&lt;string&gt; multi("file names");
cmd.add( multi );
cmd.parse(argc, argv);
vector&lt;string&gt; fileNames = multi.getValue();
</pre><p>
You must only ever specify one (1) <code class="classname">UnlabeledMultiArg</code>.
One <code class="classname">UnlabeledMultiArg</code> will read every unlabeled
Arg that wasn't already processed by a
<code class="classname">UnlabeledValueArg</code> into a
<code class="classname">vector</code> of type T. Any
<code class="classname">UnlabeledValueArg</code> or other
<code class="classname">UnlabeledMultiArg</code> specified after the first
<code class="classname">UnlabeledMultiArg</code> will be ignored, and if
they are required,
exceptions will be thrown. When you call the
<code class="methodname">getValue()</code>
method of the <code class="classname">UnlabeledValueArg</code> argument,
a <code class="classname">vector</code>
will be returned. If you can imagine a situation where there will
be multiple args of multiple types (stings, ints, floats, etc.)
then just declare the <code class="classname">UnlabeledMultiArg</code> as type
<code class="classname">string</code> and parse the different values yourself or use
several <code class="classname">UnlabeledValueArg</code>s.
</p></div></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="COMPLICATIONS"></a>Chapter 3. Complications</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#COMBINE_SWITCHES">I want to combine multiple switches into one argument...</a></span></dt><dt><span class="sect1"><a href="#XOR">I want one argument or the other, but not both...</a></span></dt><dt><span class="sect1"><a href="#NO_FLAG">I have more arguments than single flags make sense for...</a></span></dt><dt><span class="sect1"><a href="#CONSTRAINT">I want to constrain the values allowed for a particular
argument...</a></span></dt><dt><span class="sect1"><a href="#ARG_ADD_CMDLINE">I want the Args to add themselves to the CmdLine...</a></span></dt><dt><span class="sect1"><a href="#CHANGE_OUTPUT">I want different output than what is provided...</a></span></dt><dt><span class="sect1"><a href="#NO_HELP_VERSION">I don't want the --help and --version switches to be created automatically...</a></span></dt><dt><span class="sect1"><a href="#IGNORE_ARGS">I want to ignore certain arguments...</a></span></dt><dt><span class="sect1"><a href="#READING_HEX_INTEGERS">I want to read hex integers as arguments...</a></span></dt><dt><span class="sect1"><a href="#USING_ARGTRAITS">I want to use different types...</a></span></dt><dt><span class="sect1"><a href="#CHANGING_STARTSTRINGS">I want to use Windows-style flags like "/x" and "/y"...</a></span></dt></dl></div><p>
Naturally, what we have seen to this point doesn't satisfy all of
our needs.
</p><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="COMBINE_SWITCHES"></a>I want to combine multiple switches into one argument...</h2></div></div></div><p>
Multiple <code class="classname">SwitchArg</code>s can be combined into a
single argument on the command line. If you have switches -a, -b and -c
it is valid to do either:
</p><pre class="programlisting">
% command -a -b -c
</pre><p>
<span class="emphasis"><em>or</em></span>
</p><pre class="programlisting">
% command -abc
</pre><p>
<span class="emphasis"><em>or</em></span>
</p><pre class="programlisting">
% command -ba -c
</pre><p>
This is to make this library more in line with the POSIX and GNU
standards (as I understand them).
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="XOR"></a>I want one argument or the other, but not both...</h2></div></div></div><p>
Suppose you have a command that must read input from one of two
possible locations, either a local file or a URL. The command
<span class="emphasis"><em>must</em></span> read something, so <span class="emphasis"><em>one</em></span>
argument is required, but
not both, yet neither argument is strictly necessary by itself.
This is called "exclusive or" or "XOR". To accommodate this
situation, there is now an option to add two or more
<code class="classname">Arg</code>s to
a <code class="classname">CmdLine</code> that are exclusively or'd with one another:
<code class="methodname">xorAdd()</code>. This means that exactly one of the
<code class="classname">Arg</code>s must be set and no more.
</p><p>
<code class="methodname">xorAdd()</code> comes in two flavors, either
<code class="methodname">xorAdd(Arg&amp; a, Arg&amp; b)</code>
to add just two <code class="classname">Arg</code>s to be xor'd and
<code class="methodname">xorAdd( vector&lt;Arg*&gt; xorList )</code>
to add more than two <code class="classname">Arg</code>s.
</p><pre class="programlisting">
ValueArg&lt;string&gt; fileArg("f","file","File name to read",true,"/dev/null", "filename");
ValueArg&lt;string&gt; urlArg("u","url","URL to load",true, "http://example.com", "URL");
cmd.xorAdd( fileArg, urlArg );
cmd.parse(argc, argv);
</pre><p>
Once one <code class="classname">Arg</code> in the xor list is matched on the
<code class="classname">CmdLine</code> then the others in the xor list will be
marked as set. The question then, is how to determine which of the
<code class="classname">Arg</code>s has been set? This is accomplished by calling the
isSet() method for each <code class="classname">Arg</code>. If the
<code class="classname">Arg</code> has been
matched on the command line, the <code class="methodname">isSet()</code> will return
<code class="constant">TRUE</code>, whereas if the <code class="classname">Arg</code>
has been set as a result of matching the other <code class="classname">Arg</code>
that was xor'd <code class="methodname">isSet()</code> will
return <code class="constant">FALSE</code>.
(Of course, if the <code class="classname">Arg</code> was not xor'd and
wasn't matched, it will also return <code class="constant">FALSE</code>.)
</p><pre class="programlisting">
if ( fileArg.isSet() )
readFile( fileArg.getValue() );
else if ( urlArg.isSet() )
readURL( urlArg.getValue() );
else
// Should never get here because TCLAP will note that one of the
// required args above has not been set.
throw("Very bad things...");
</pre><p>
It is helpful to note that <code class="classname">Arg</code>s of any type can be xor'd together.
This means that you can xor a <code class="classname">SwitchArg</code> with a <code class="classname">ValueArg</code>.
This is helpful in situations where one of several options is necessary and one of the options
requires additional information.
</p><pre class="programlisting">
SwitchArg stdinArg("s", "stdin", "Read from STDIN", false);
ValueArg&lt;string&gt; fileArg("f","file","File name to read",true,"/dev/null", "filename");
ValueArg&lt;string&gt; urlArg("u","url","URL to load",true, "http://example.com", "URL");
vector&lt;Arg*&gt; xorlist;
xorlist.push_back(&amp;stdinArg);
xorlist.push_back(&amp;fileArg);
xorlist.push_back(&amp;urlArg);
cmd.xorAdd( xorlist );
</pre><p>
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="NO_FLAG"></a>I have more arguments than single flags make sense for...</h2></div></div></div><p>
Some commands have so many options that single flags no longer map
sensibly to the available options. In this case, it is desirable to
specify <code class="classname">Arg</code>s using only long options. This one is easy to
accomplish, just make the flag value blank in the <code class="classname">Arg</code>
constructor. This will tell the <code class="classname">Arg</code> that only the long
option should be matched and will force users to specify the long
option on the command line. The help output is updated accordingly.
</p><pre class="programlisting">
ValueArg&lt;string&gt; fileArg("","file","File name",true,"homer","filename");
SwitchArg caseSwitch("","upperCase","Print in upper case",false);
</pre><p>
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="CONSTRAINT"></a>I want to constrain the values allowed for a particular
argument...</h2></div></div></div><p>
<span class="emphasis"><em>Interface Change!!!</em></span> Sorry folks, but we've changed
the interface since version 1.0.X for constraining <code class="classname">Arg</code>s.
Constraints are now hidden behind the <code class="classname">Constraint</code>
interface. To
constrain an <code class="classname">Arg</code> simply implement the interface
and specify the new class in the constructor as before.
</p><p>
You can still constrain <code class="classname">Arg</code>s based on
a list of values. Instead of adding a <code class="classname">vector</code> of
allowed values to the <code class="classname">Arg</code> directly,
create a <code class="classname">ValuesConstraint</code> object
with a <code class="classname">vector</code> of values and add that to the
<code class="classname">Arg</code>. The <code class="classname">Arg</code> constructors
have been modified accordingly.
</p><p>
When the value for the
<code class="classname">Arg</code> is parsed,
it is checked against the list of values specified in the
<code class="classname">ValuesConstraint</code>.
If the value is in the list then it is accepted. If
not, then an exception is thrown. Here is a simple example:
</p><pre class="programlisting">
vector&lt;string&gt; allowed;
allowed.push_back("homer");
allowed.push_back("marge");
allowed.push_back("bart");
allowed.push_back("lisa");
allowed.push_back("maggie");
ValuesConstraint&lt;string&gt; allowedVals( allowed );
ValueArg&lt;string&gt; nameArg("n","name","Name to print",true,"homer",&amp;allowedVals);
cmd.add( nameArg );
</pre><p>
When a <code class="classname">ValuesConstraint</code> is specified,
instead of a type description being specified in the
<code class="classname">Arg</code>, a
type description is created by concatenating the values in the
allowed list using operator&lt;&lt; for the specified type. The
help/usage for the <code class="classname">Arg</code> therefore lists the
allowable values. Because of this, you might want to keep the list
relatively small, however there is no limit on this.
</p><p>
Obviously, a list of allowed values isn't always the best way to
constrain things. For instance, one might wish to allow only
integers greater than 0. In this case, simply create a class that
implements the <code class="classname">Constraint&lt;int&gt;</code> interface and
checks whether the value parsed is greater than 0 (done in the
<code class="methodname">check()</code> method) and create your
<code class="classname">Arg</code> with your new <code class="classname">Constraint</code>.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="ARG_ADD_CMDLINE"></a>I want the Args to add themselves to the CmdLine...</h2></div></div></div><p>
New constructors have been added for each <code class="classname">Arg</code>
that take a <code class="classname">CmdLine</code> object as an argument.
Each <code class="classname">Arg</code> then
<code class="methodname">add</code>s itself to the <code class="classname">CmdLine</code>
object. There is no difference in how the <code class="classname">Arg</code>
is handled between this method and calling the
<code class="methodname">add()</code> method directly. At the moment, there is
no way to do an <code class="methodname">xorAdd()</code> from the constructor. Here
is an example:
</p><pre class="programlisting">
// Create the command line.
CmdLine cmd("this is a message", '=', "0.99" );
// Note that the following args take the "cmd" object as arguments.
SwitchArg btest("B","existTestB", "exist Test B", cmd, false );
ValueArg&lt;string&gt; stest("s", "stringTest", "string test", true, "homer",
"string", cmd );
UnlabeledValueArg&lt;string&gt; utest("unTest1","unlabeled test one",
"default","string", cmd );
// NO add() calls!
// Parse the command line.
cmd.parse(argc,argv);
</pre><p>
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="CHANGE_OUTPUT"></a>I want different output than what is provided...</h2></div></div></div><p>
It is straightforward to change the output generated by
<span class="emphasis"><em>TCLAP</em></span>. Either subclass the
<code class="classname">StdOutput</code> class and re-implement the methods you choose,
or write your own class that implements the
<code class="classname">CmdLineOutput</code> interface. Once you have done this,
then use the <code class="classname">CmdLine</code> <code class="methodname">setOutput</code>
method to tell the <code class="classname">CmdLine</code> to use your new output
class. Here is a simple example:
</p><pre class="programlisting">
class MyOutput : public StdOutput
{
public:
virtual void failure(CmdLineInterface&amp; c, ArgException&amp; e)
{
cerr &lt;&lt; "My special failure message for: " &lt;&lt; endl
&lt;&lt; e.what() &lt;&lt; endl;
exit(1);
}
virtual void usage(CmdLineInterface&amp; c)
{
cout &lt;&lt; "my usage message:" &lt;&lt; endl;
list&lt;Arg*&gt; args = c.getArgList();
for (ArgListIterator it = args.begin(); it != args.end(); it++)
cout &lt;&lt; (*it)-&gt;longID()
&lt;&lt; " (" &lt;&lt; (*it)-&gt;getDescription() &lt;&lt; ")" &lt;&lt; endl;
}
virtual void version(CmdLineInterface&amp; c)
{
cout &lt;&lt; "my version message: 0.1" &lt;&lt; endl;
}
};
int main(int argc, char** argv)
{
CmdLine cmd("this is a message", ' ', "0.99" );
// set the output
MyOutput my;
cmd.setOutput( &amp;my );
// proceed normally ...
</pre><p>
See <code class="filename">test4.cpp</code> in the examples directory for the full
example. <span class="emphasis"><em>NOTE</em></span>: if you supply your own Output object, we
will not delete it in the <code class="classname">CmdLine</code> destructor. This
could lead to a (very small) memory leak if you don't take care of the object
yourself. Also note that the <code class="methodname">failure</code> method is
now responsible for exiting the application (assuming that is the desired
behavior).
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="NO_HELP_VERSION"></a>I don't want the --help and --version switches to be created automatically...</h2></div></div></div><p>
Help and version information is useful for nearly all command line applications
and as such we generate flags that provide those options automatically.
However, there are situations when these flags are undesirable. For these
cases we've added we've added a forth parameter to the
<code class="classname">CmdLine</code> constructor. Making this boolean parameter
false will disable automatic help and version generation.
</p><pre class="programlisting">
CmdLine cmd("this is a message", ' ', "0.99", false );
</pre><p>
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="IGNORE_ARGS"></a>I want to ignore certain arguments...</h2></div></div></div><p>
The <em class="parameter"><code>--</code></em> flag is automatically included in the
<code class="classname">CmdLine</code>.
As (almost) per POSIX and GNU standards, any argument specified
after the <em class="parameter"><code>--</code></em> flag is ignored.
<span class="emphasis"><em>Almost</em></span> because if an
<code class="classname">UnlabeledValueArg</code> that has not been set or an
<code class="classname">UnlabeledMultiArg</code> has been specified, by default
we will assign any arguments beyond the <em class="parameter"><code>--</code></em>
to the those arguments as
per the rules above. This is primarily useful if you want to pass
in arguments with a dash as the first character of the argument. It
should be noted that even if the <em class="parameter"><code>--</code></em> flag is
passed on the command line, the <code class="classname">CmdLine</code> will
<span class="emphasis"><em>still</em></span> test to make sure all of the required
arguments are present.
</p><p>
Of course, this isn't how POSIX/GNU handle things, they explicitly
ignore arguments after the <em class="parameter"><code>--</code></em>. To accommodate this,
we can make both <code class="classname">UnlabeledValueArg</code>s and
<code class="classname">UnlabeledMultiArg</code>s ignoreable in their constructors.
See the <a href="html/index.html" target="_top"> API Documentation</a> for details.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="READING_HEX_INTEGERS"></a>I want to read hex integers as arguments...</h2></div></div></div><p>
Sometimes it's desirable to read integers formatted in decimal, hexadecimal,
and octal format. This is now possible by #defining the <em class="parameter"><code>TCLAP_SETBASE_ZERO</code></em>
directive. Simply define this directive in your code and integer arguments will be parsed
in each base.
</p><pre class="programlisting">
#define TCLAP_SETBASE_ZERO 1
#include "tclap/CmdLine.h"
#include &lt;iostream&gt;
using namespace TCLAP;
using namespace std;
int main(int argc, char** argv)
{
try {
CmdLine cmd("this is a message", ' ', "0.99" );
ValueArg&lt;int&gt; itest("i", "intTest", "integer test", true, 5, "int");
cmd.add( itest );
//
// Parse the command line.
//
cmd.parse(argc,argv);
//
// Set variables
//
int _intTest = itest.getValue();
cout &lt;&lt; "found int: " &lt;&lt; _intTest &lt;&lt; endl;
} catch ( ArgException&amp; e )
{ cout &lt;&lt; "ERROR: " &lt;&lt; e.error() &lt;&lt; " " &lt;&lt; e.argId() &lt;&lt; endl; }
}
</pre><p>
</p><p>
The reason that this behavior is not the default behavior for <span class="emphasis"><em>TCLAP</em></span> is that the use of
<code class="methodname">setbase(0)</code> appears to be something of a side effect and is not necessarily how
<code class="methodname">setbase()</code> is meant to be used. So while we're making this functionality
available, we're not turning it on by default for fear of bad things happening in different compilers.
If you know otherwise, please let us know.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="USING_ARGTRAITS"></a>I want to use different types...</h2></div></div></div><p>
The usual C++ types (int, long, bool, etc.) are supported by <span class="emphasis"><em>TCLAP</em></span> out
of the box. As
long as operator&gt;&gt; and operator&lt;&lt; are supported, other types should work fine
too, you'll just need to specify the <code class="classname">ArgTraits</code> which
tells <span class="emphasis"><em>TCLAP</em></span> how you expect the type to be handled.
</p><p>
For example, assume that you'd like to read one argument on the command line in as a
<code class="classname">std::pair</code> object. All you'll need to do is tell
<span class="emphasis"><em>TCLAP</em></span> whether to treat <code class="classname">std::pair</code> as a
String or Value. StringLike means to treat the string on the command line as a string
and use it directly, whereas ValueLike means that a value object should be extracted from the
string using operator&gt;&gt;. For <code class="classname">std::pair</code> we'll choose ValueLike.
To accomplish this, add the following declaration to your file:
</p><pre class="programlisting">
template&lt;class T, class U&gt;
struct ArgTraits&lt;std::pair&lt;T, U&gt;&gt; {
typedef ValueLike ValueCategory;
};
</pre><p>
For complete examples see the files <code class="filename">test11.cpp</code>
and <code class="filename">test12.cpp</code> in the examples directory.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="CHANGING_STARTSTRINGS"></a>I want to use Windows-style flags like "/x" and "/y"...</h2></div></div></div><p>
It is traditional in Posix environments that the "-" and "--" strings are used to signify
the beginning of argument flags and long argument names. However, other environments,
namely Windows, use different strings. <span class="emphasis"><em>TCLAP</em></span> allows you to
control which strings are used with <code class="methodname">#define</code> directives. This allows
you to use different strings based on your operating environment. Here is an example:
</p><pre class="programlisting">
//
// This illustrates how to change the flag and name start strings for
// Windows, otherwise the defaults are used.
//
// Note that these defines need to happen *before* tclap is included!
//
#ifdef WINDOWS
#define TCLAP_NAMESTARTSTRING "~~"
#define TCLAP_FLAGSTARTSTRING "/"
#endif
#include "tclap/CmdLine.h"
using namespace TCLAP;
using namespace std;
int main(int argc, char** argv)
{
// Everything else is identical!
...
</pre><p>
</p></div></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="NOTES"></a>Chapter 4. Notes</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#DESCRIPTION_EXCEPTIONS">Type Descriptions</a></span></dt><dt><span class="sect1"><a href="#VISITORS">Visitors</a></span></dt><dt><span class="sect1"><a href="#MORE_INFO">More Information</a></span></dt></dl></div><p>
Like all good rules, there are many exceptions....
</p><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="DESCRIPTION_EXCEPTIONS"></a>Type Descriptions</h2></div></div></div><p>
Ideally this library would use RTTI to return a human readable name
of the type declared for a particular argument. Unfortunately, at
least for <span><strong class="command">g++</strong></span>, the names returned aren't
particularly useful.
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="VISITORS"></a>Visitors</h2></div></div></div><p>
Disclaimer: Almost no one will have any use for
<code class="classname">Visitor</code>s, they were
added to provide special handling for default arguments. Nothing
that <code class="classname">Visitor</code>s do couldn't be accomplished
by the user after the
command line has been parsed. If you're still interested, keep
reading...
</p><p>
Some of you may be wondering how we get the <em class="parameter"><code>--help</code></em>,
<em class="parameter"><code>--version</code></em> and <em class="parameter"><code>--</code></em>
arguments to do their thing without mucking up the
<code class="classname">CmdLine</code> code with lots of <span class="emphasis"><em>if</em></span>
statements and type checking. This is accomplished by using a
variation on the Visitor Pattern. Actually, it may not be a Visitor
Pattern at all, but that's what inspired me.
</p><p>
If we want some argument to do some sort of special handling,
besides simply parsing a value, then we add a <code class="classname">Visitor</code>
pointer to the <code class="classname">Arg</code>. More specifically, we add a
<span class="emphasis"><em>subclass</em></span> of the <code class="classname">Visitor</code>
class. Once the argument has been successfully parsed, the
<code class="classname">Visitor</code> for that argument is
called. Any data that needs to be operated on is declared in the
<code class="classname">Visitor</code> constructor and then operated on in the
<code class="methodname">visit()</code> method. A <code class="classname">Visitor</code>
is added to an <code class="classname">Arg</code> as the last argument in its
declaration. This may sound
complicated, but it is pretty straightforward. Let's see an
example.
</p><p>
Say you want to add an <em class="parameter"><code>--authors</code></em> flag to a program that
prints the names of the authors when present. First subclass
<code class="classname">Visitor</code>:
</p><pre class="programlisting">
#include "Visitor.h"
#include &lt;string&gt;
#include &lt;iostream&gt;
class AuthorVisitor : public Visitor
{
protected:
string _author;
public:
AuthorVisitor(const string&amp; name ) : Visitor(), _author(name) {} ;
void visit() { cout &lt;&lt; "AUTHOR: " &lt;&lt; _author &lt;&lt; endl; exit(0); };
};
</pre><p>
Now include this class definition somewhere and go about creating
your command line. When you create the author switch, add the
<code class="classname">AuthorVisitor</code> pointer as follows:
</p><pre class="programlisting">
SwitchArg author("a","author","Prints author name", false,
new AuthorVisitor("Homer J. Simpson") );
cmd.add( author );
</pre><p>
Now, any time the <em class="parameter"><code>-a</code></em> or
<em class="parameter"><code>--author</code></em> flag is specified,
the program will print the author name, Homer J. Simpson and exit
without processing any further (as specified in the
<code class="methodname">visit()</code> method).
</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="MORE_INFO"></a>More Information</h2></div></div></div><p>
For more information, look at the <a href="html/index.html" target="_top">
API Documentation</a> and the examples included with the
distribution.
</p><p>
<span class="emphasis"><em>Happy coding!</em></span>
</p></div></div></div></body></html>