By default guessing is enabled, in which case you cant have two options with a common prefix, as it assumes the shorter one is the same as the full one when the user enters it.

Use the allow_guessing style to avoid, see here:
http://www.boost.org/doc/libs/1_43_0/doc/html/boost/program_options/command_line_style/style_t.html

I did this to avoid it:

// disable guessing of option names
int cmdstyle =
�po::command_line_style::default_style &
�~po::command_line_style::allow_guessing;

store(po::command_line_parser(ac, av).
�style(cmdstyle).options(cmdline_options).
�positional(p).run(), vm);

-Sanjit

On Thu, Mar 31, 2011 at 4:16 PM, Sanjit Jhala <sjhalaz@gmail.com> wrote:

Hi,

I have the following code (modified from example/first.cpp):

#include <boost/program_options.hpp>

#include <string>
#include <vector>

#include <iostream>

namespace po = boost::program_options;

using namespace std;

typedef vector<string> Strings;

// A helper function to simplify the main part.
template<class T>
ostream& operator<<(ostream& os, const vector<T>& v)

{
��copy(v.begin(), v.end(), ostream_iterator<T>(cout, " "));
��return os;�
}

int main(int argc, char *argv[]) {

��po::options_description cmdline_desc("Usage: %s [Options] [args]\nOptions");
��cmdline_desc.add_options()
�� ("str", po::value< string >(), "a string arg")

�� ("strs", po::value< Strings >(), "a list of strings")
�� ("foo", po::value< string >(), "a string arg")
�� ("bar", po::value< Strings >(), "a list of strings")

�� ; ��

��po::variables_map vm;�
��po::store(po::parse_command_line(argc, argv, cmdline_desc), vm);
��po::notify(vm);

��if (vm.count("str"))
�� cout << "Got str arg=" << vm["str"].as< string >() << "\n";
��if (vm.count("strs"))

�� cout << "Got strs arg=" << vm["strs"].as< Strings >() << "\n";
��if (vm.count("foo"))
�� cout << "Got foo arg=" << vm["foo"].as< string >() << "\n";

��if (vm.count("bar"))
�� cout << "Got bar arg=" << vm["bar"].as< Strings >() << "\n";
}

When I run the program I see:
./po_test --str "a string" --strs "a, vector, of, strings" --foo "a foo" --bar "a, bar"
Got strs arg=a string a, vector, of, strings�

Got foo arg=a foo
Got bar arg=a, bar�

It appears the parser is getting confused between the "str" and the "strs". It doesn't seem to be related to ambiguity in handling vectors since the "foo" and "bar" arguments are fine. I see this problem on 32-bit CentOS and Ubuntu machines, but not on 64-bit. I am running Boost 1.43 and from the�/usr/local/include/boost/program_options/version.hpp:

#define BOOST_PROGRAM_OPTIONS_VERSION_HPP_VP_2004_04_05
#define BOOST_PROGRAM_OPTIONS_VERSION 2

Is this a bug or a expected behaviour?

-Sanjit