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<table><tr><td align="left">
<h1>Templatized C++ Command Line Parser Examples</h1>
</td><td align="right">
<A href="http://sourceforge.net"> <IMG
src="http://sourceforge.net/sflogo.php?group_id=76645&amp;type=4"
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</td></tr></table>
<h2>Basic usage</h2>
There are a few key classes to be aware of. The first is the <b>CmdLine</b>
or command line class. This is the class that parses the command line
passed to it according to the arguments that it contains. Arguments are
separate objects that are added to <b>CmdLine</b> object one at a time. There
are five types of arguments, <b>ValueArg</b>, <b>UnlabeledValueArg</b>,
<b>SwitchArg</b>, <b>MultiArg</b> and <b>UnlabeledMultiArg</b>.
Once the arguments are added to the command line object,
the command line is parsed which assigns the data on the command line to
the specific argument objects. The values are accessed by calls to
the <i>getValue()</i> methods of the argument objects.
<br> <br>
Here is a simple <a href="test1.cpp">example</a> ...
<br> <br>
<pre>
#include < string >
#include < iostream >
#include < tclap/CmdLine.h >
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.
CmdLine cmd("Command description message", ' ', "0.9");
// (deprecated, but still functional)
// CmdLine cmd(argv[0], "Command description message", "0.9");
// Define a value argument and add it to the command line.
ValueArg < string > nameArg("n","name","Name to print",true,"homer",
"nameString");
cmd.add( nameArg );
// Define a switch and add it to the command line.
SwitchArg caseSwitch("u","upperCase","Print in upper case", false);
cmd.add( caseSwitch );
// Parse the args.
cmd.parse( argc, argv );
// Get the value parsed by each arg.
string name = nameArg.getValue();
bool upperCase = caseSwitch.getValue();
// Do what you intend too...
if ( upperCase )
transform(name.begin(),name.end(),name.begin(),::toupper);
else
transform(name.begin(),name.end(),name.begin(),::tolower);
cout << "My name is " << name << endl;
} catch (ArgException e) // catch any exceptions
{ cerr << "error: " << e.error() << " for arg " << e.argId() << endl; }
}
</pre>
<br><br><br>
The output should look like:
<br><br><br>
<pre>
% tester -u -n mike
My name is MIKE
% tester -n mike -u
My name is MIKE
% tester -n mike
My name is mike
% tester -n MIKE
My name is mike
% tester
PARSE ERROR: for argument: undefined
One or more required arguments missing!
USAGE:
test1 [-u] -n < nameString > [--] [-v] [-h]
Where:
-u, --upperCase
Print in upper case
-n < nameString >, --name < nameString >
(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>
<br><br><br>
This example shows a number of different properties of the library...
<ul>
<li><b>New Feature!</b> Note that the creation of the CmdLine object is
slightly different now. The program name is assumed to always be
argv[0], so it isn't specified directly (let me know if you don't like
this). More importantly, a delimiter character can now be specified.
this means that if you prefer arguments of the style "-s=asdf" instead
of "-s asdf", you can do so.
<li>Arguments can appear in any order (...mostly, <a href="manual.html#COMPLICATIONS">more</a> on this later).</li>
<li>The version, help and -- arguments are specified automatically.</li>
<li>If a required argument isn't provided, the program exits and displays
the USAGE, along with an error message.</li>
</ul>
<h3><i>Basic Properties</i></h3>
Arguments, whatever their type, have a few common basic properties. First
is the flag or the character preceeded by a dash(-) that signals the beginning
of the argument. Arguments also have names, which can, if desired also be
used as a flag on the command line, this time preceeded by two dashes (--)
[like the familiar getopt_long()].
Next is the description of the argument. This is a short description of
the argument displayed in the help/usage
message when needed. The boolean value in <b>ValueArg</b>s indicates
whether the argument is required to be present (<b>SwitchArg</b>s can't
be required, as that would defeat the purpose). Next, the default
value the arg should assume if the arg isn't required or entered on the
command line. Last, for <b>ValueArg</b>s is a short description of the type
that the argument expects (yes its an ugly
<a href="manual.html#DESCRIPTION_EXCEPTIONS">hack</a>).
<br><br>
<b>SwitchArg</b>s are what the name implies, simple on/off, boolean switches.
Use <b>SwitchArg</b>s anytime you want to turn some sort of system property
on or off. Note that multiple <b>SwitchArg</b>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:
<br><br>
<pre>
% command -a -b -c
</pre>
<br><br>
<i>or</i>
<br><br>
<pre>
% command -abc
</pre>
<br><br>
<i>or</i>
<br><br>
<pre>
% command -ba -c
</pre>
<br><br>
This is to make this library more in line with the POSIX and GNU standards (as
I understand them).
<br><br>
<b>ValueArg</b>s are arguments that read a value of some type from the
command line. Note that the order of arguments on the command line (so far)
doesn't matter. Any
argument not matching an <b>Arg</b> added to the command line will cause
an exception to be thrown
(<a href="manual.html#COMPLICATIONS">for the most part</a>, with some
<a href="manual.html#EXCEPTIONS">exceptions</a>).
<br> <br>
Note in the output of the USAGE above, that there are three arguments that
were not explicitly specified by the user in the code.
These are the <i>help</i>
and <i>version</i> and <i>--</i> <b>SwitchArg</b>s. Using either the
<i>-h</i> or
<i>--help</i> flag will cause the USAGE message to be displayed
and <i>-v</i> or <i>--version</i> will cause
any version information to be displayed and <i>--</i> or <i>--ignore_rest</i>
will cause the remaining labeled arguments to be ingored.
These switches are included
automatically on every command line. Currently there is no way to turn this
off, but then, thats kind of the point.
More <a href="manual.html#VISITORS">later</a> on how we get this to work.
<a name="COMPLICATIONS"></a>
<h2>Complications</h2>
Naturally, what we have seen to this point doesn't satisfy all of our needs.
<h3><i>I tried passing multiple values on the command line with the same flag and it didn't work...</i></h3>
Correct. You can neither specify mulitple <b>ValueArg</b>s or
<b>SwitchArg</b>s with the same flag in the code nor on the command line.
Exceptions will occur in either case. For <b>SwitchArg</b>s it simply doesn't
make sense to allow a particular flag to be turned on or off repeatedly on
the command
line. All you should ever need is to set your state <i>once</i> by specifying
the flag or not (<a href="manual.html#EXCEPTIONS">yeah but...</a>).
<br><br>
However, there <i>are</i> situations where you might want
multiple values for the same flag to be specified. Imagine a compiler that
allows you to specify multiple directories to search for libraries...
<br> <br>
<pre>
% fooCompiler -L /dir/num1 -L /dir/num2 file.foo
</pre>
<br> <br>
In situations like this, you will want to use a <b>MultiArg</b>. A
<b>MultiArg</b> is essentially a <b>ValueArg</b> that appends any value
that it matches and parses onto a vector of values. When the <i>getValue()</i>
method id called, a vector of values, instead of a single value is returned.
A <b>MultiArg</b> is declared much like a <b>ValueArg</b>:
<br><br>
<pre>
...
MultiArg < int > itest("i", "intTest", "multi int test", false,"int" );
cmd.add( itest );
...
</pre>
<br><br>
Note that <b>MultiArg</b>s can be added to the <b>CmdLine</b> in any
order (unlike <a href="manual.html#UNLABELED_MULTI_ARG">UnlabeledMultiArg</a>s).
<h3><i>But I don't like labelling all of my arguments...</i> </h3>
To this point all of our arguments have had labels (flags) indentifying 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
<i>copy</i>. All <i>copy</i> does is copy the file specified in the first
argument to the file specified in the second argument. We can do this using
<b>UnlabeledValueArg</b>s which are pretty much just <b>ValueArg</b>s without
the flag specified, which tells the
<b>CmdLine</b> object to treat them accordingly. The code would look like
this:
<br><br>
<pre>
...
UnlabeledValueArg < float > nolabel( "name", "unlabeled test", 3.14,
"nameString" );
cmd.add( nolabel );
...
</pre>
<br><br>
Everything else is handled identically to what is seen above. The only
difference to be aware of, and this is important: <b>the order that
UnlabeledValueArgs are added to the <i>CmdLine</i> is the order that
they will be parsed!!!!</b> This is <i>not</i> the case for normal
<b>SwitchArg</b>s and <b>ValueArg</b>s. What happens internally is the
first argument that the <b>CmdLine</b> doesn't recognize is assumed to be the
first <b>UnlabeledValueArg</b> and parses it as such. Note that you
are allowed to intersperse labeled args (SwitchArgs and ValueArgs) in
between <b>UnlabeledValueArgs</b> (either
on the command line or in the declaration), but the <b>UnlabeledValueArgs</b>
will still be parsed in the order they are added. Just remember that order
is important for unlabeled arguments.
<a name="UNLABELED_MULTI_ARG"></a>
<h3><i>But I want an arbitrary number of arguments to be accepted...</i></h3>
Don't worry, we've got you covered. Say you want a strange command that
searches each file specified for a given string (lets call it <i>grep</i>),
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,
<br><br>
<pre>
% grep pattern *.txt
</pre>
<br><br>
First remember that the <b>*</b> is handled by the shell and expanded
accordingly, so what the program <i>grep</i> sees is really something
like:
<br><br>
<pre>
% grep pattern file1.txt file2.txt fileZ.txt
</pre>
<br><br>
To handle situations where multiple, unlabled arguments are needed, we
provide the <b>UnlabeledMultiArg</b>. <b>UnlabeledMultiArg</b>s are declared
much like
everything else, but with only a description of the arguments. By default,
if an <b>UnlabeledMultiArg</b> 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 <b>UnlabeledValueArg</b>s: order matters! In fact, <b>an
UnlabeledMultiArg must be the <i>last</i> argument added to the CmdLine!</b>.
Here is what a declaration looks like:
<br> <br> <br> <br>
<pre>
...
//
// UnlabeledMultiArg must be the LAST argument added!
//
UnlabeledMultiArg < string > multi("file names");
cmd.add( multi );
cmd.parse(argc, argv);
vector < string > fileNames = multi.getValue();
...
</pre>
<br> <br> <br> <br>
You must only ever specify one (1) <b>UnlabeledMultiArg</b>.
One <b>UnlabeledMultiArg</b> will
read every unlabeled Arg that wasn't already processed by a
<b>UnlabeledValueArg</b>
into a <i>vector</i> of type T.
Any <b>UnlabeledValueArg</b> or other <b>UnlabeledMultiArg</b> specified after
the first <b>UnlabeledMultiArg</b> will be ignored, and if they are required,
expections will be thrown.
When you call the <i>getValue()</i> method
of the <b>UnlabeledValueArg</b>
argument, a <i>vector</i> 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 <b>UnlabeledMultiArg</b> as type
<i>string</i>
and parse the different values yourself.
<a name="XOR"></a>
<h3><i>I want one argument or the other, but not both...</i></h3>
<b>New Feature!</b> Suppose you have a command that must read input from one
of two possible locations, either a local file or a URL. The command
<i>must</i> read something, so <i>one</i> argument is required, but not both,
yet neither argument is strictly necessary by itself. This is called
"exclusive or" or "XOR". To accomodate this situation, there is now an
option to add two or more <b>Arg</b>s to a <b>CmdLine</b> that are exclusively
or'd with one another: xorAdd(). This means that at exactly one of
the <b>Arg</b>s must be set and no more.
<br> <br>
xorAdd() comes in two flavors, either xorAdd(Arg& a, Arg& b) to add just
two <b>Arg</b>s to be xor'd and xorAdd( vector<Arg*> xorList ) to add more
than two <b>Arg</b>s.
<br> <br>
<pre>
...
ValueArg < string > fileArg("f","file","File name to read",true,"homer",
"filename");
ValueArg < string > urlArg("u","url","URL to load",true,
"http://example.com", "URL");
cmd.xorAdd( fileArg, urlArg );
cmd.parse(argc, argv);
...
</pre>
<br> <br>
Once one <b>Arg</b> in the xor list is matched on the <b>CmdLine</b> then
the others in the xor list will be marked as set. The question then, is how to
determine which of the <b>Arg</b>s has been set? This is accomplished by
calling the isSet() method for each <b>Arg</b>. If the <b>Arg</b> has been
matched on the command line, the isSet() will return <b>TRUE</b>, whereas
if the <b>Arg</b> has been set as a result of matching the other <b>Arg</b>
that was xor'd isSet() will return <b>FALSE</b>. (Of course, if the <b>Arg</b>
was not xor'd and wasn't matched, it will also return <b>FALSE</b>.)
<br> <br>
<pre>
...
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>
<br> <br>
<a name="NO_FLAG"></a>
<h3><i>I have more arguments than single flags make sense for...</i></h3>
<b>New Feature!</b> 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 <b>Arg</b>s using only long options.
This one is easy to accomplish, just make the flag value blank in
the <b>Arg</b> constructor. This will tell the <b>Arg</b> that only the
long option should be matched and will force users to specify the long
option on the command line</b>.
The help output is updated accordingly.
<br> <br>
<pre>
...
ValueArg < string > fileArg("","file","File name",true,"homer","filename");
SwitchArg caseSwitch("","upperCase","Print in upper case",false);
...
</pre>
<br> <br>
<a name="VISITORS"></a>
<h2>Visitors</h2>
Disclaimer: Almost no one will have any use for Visitors, they were added
to provide special handling for default arguments. Nothing that Visitors
do couldn't be accomplished by the user after the command line has been parsed.
If you're still interested, keep reading...
<br><br>
Some of you may be wondering how we get the <i>--help</i>, <i>--version</i>
and <i>--</i>
arguments to do their thing without mucking up the <b>CmdLine</b> code
with lots of <i>if</i> 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 thats what inspired me.
<br> <br>
If we want some argument to do some sort of special handling, besides simply
parsing a value, then we add a <b>Visitor</b> pointer to the <b>Arg</b>.
More specifically, we add a <i>subclass</i> of the <b>Visitor</b> class.
Once the argument has been successfully parsed, the <b>Visitor</b> for
that argument is called.
Any data that needs to be operated on is declared in the <b>Visitor</b>
constructor and then operated on in the <i>visit()</i> method. A
<b>Visitor</b> is added to an <b>Arg</b> as the last argument in its
declaration. This may sound complicated, but its pretty straightforward.
Lets see an example.
<br><br>
Say you want to add an <i>--authors</i> flag to a program that prints the
names of the authors when present. First subclass <b>Visitor</b>:
<br> <br>
<pre>
#include "Visitor.h"
#include < string >
#include < iostream >
class AuthorVisitor : public Visitor
{
protected:
string _author;
public:
AuthorVisitor(const string& name ) : Visitor(), _author(name) {} ;
void visit() { cout << "AUTHOR: " << _author << endl; exit(0); };
};
</pre>
<br> <br>
Now include this class definition somewhere and go about creating your
command line. When you create the author switch, add the <b>AuthorVisitor</b>
pointer as follows:
<br><br>
<pre>
...
SwitchArg author("a","author","Prints author name", false,
new AuthorVisitor("Homer J. Simpson") );
cmd.add( author );
...
</pre>
<br><br>
<br><br>
Now, any time the <i>-a</i> or <i>--author</i> flag is specified, the
program will print the author name, Homer J. Simpson and exit without
processing any further (as specified in the <i>visit()</i> method).
<a name="EXCEPTIONS"></a>
<h2>Exceptions</h2>
Like all good rules, there are many exceptions....
<h3><i>Ignoring arguments...</i></h3>
The <i>--</i> flag is automatically included in the <b>CmdLine</b>. As (almost)
per POSIX and GNU standards, any argument specified after the <i>--</i> flag
is ignored. <i>Almost</i> because if an <b>UnlabeledValueArg</b> that has
not been set or an <b>UnlabeledMultiArg</b> has been specified, by default
we will assign any arguments beyond the <i>--</i> 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 <i>--</i> flag is passed on the command line,
the <b>CmdLine</b> will <i>still</i> test to make sure all of the required
arguments are present.
<br><br>
Of course, this isn't how POSIX/GNU handle things, they explicitly
ignore arguments after the <i>--</i>. To accomodate this, we can make both
<b>UnlabeledValueArg</b>s and <b>UnlabeledMultiArg</b>s ignoreable in
their constructors. See
the <a href="html/index.html">API Documentation</a> for details.
<h3><i>Multiple Identical Switches</i></h3>
If you absolutely must allow for multiple, identical switches to be allowed,
don't use a <b>SwitchArg</b>, instead use a <b>MultiArg</b> of type
<i>bool</i>. This means you'll need to specify
a 1 or 0 on the command line with the switch (as values are required), but
this should allow you to turn your favorite switch on and off to your hearts
content.
<a name="DESCRIPTION_EXCEPTIONS"></a>
<h3><i>Type Descriptions</i></h3>
Ideally this library would use RTTI to return a human readable name of the
type declared for a particular argument. Unfortunately, at least for g++,
the names returned aren't particularly useful.
<h2>More Information</h2>
For more information, look at
the <a href="html/index.html">API Documentation</a>
and the examples included with the distribution.
<br><br>
<b>Happy coding!</b>
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