regex.cpp

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// Copyright Vladimir Prus 2002-2004.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)

// This example shows how a user-defined class can be parsed using
// specific mechanism -- not the iostream operations used by default.
//
// A new class 'magic_number' is defined and the 'validate' method is overloaded
// to validate the values of that class using Boost.Regex.
// To test, run
//   
//    regex -m 123-456
//    regex -m 123-4567
// 
// The first invocation should output:
//
//   The magic is "456"
//
// and the second invocation should issue an error message.

#include <boost/program_options.hpp>
#include <boost/regex.hpp>

using namespace boost;
using namespace boost::program_options;

#include <iostream>
using namespace std;

/* Define a completely non-sensical class. */
struct magic_number {
public:
    magic_number(int n) : n(n) {}
    int n;
};

/* Overload the 'validate' function for the user-defined class.
   It makes sure that value is of form XXX-XXX 
   where X are digits and converts the second group to an integer.
   This has no practical meaning, meant only to show how
   regex can be used to validate values.
*/
void validate(boost::any& v, 
              const std::vector<std::string>& values,
              magic_number* target_type, int)
{
    static regex r("\\d\\d\\d-(\\d\\d\\d)");

    using namespace boost::program_options;

    // Make sure no previous assignment to 'a' was made.
    validators::check_first_occurrence(v);
    // Extract the first string from 'values'. If there is more than
    // one string, it's an error, and exception will be thrown.
    const string& s = validators::get_single_string(values);

    // Do regex match and convert the interesting part to 
    // int.
    smatch match;
    if (regex_match(s, match, r)) {
        v = any(magic_number(lexical_cast<int>(match[1])));
    } else {
        throw validation_error("invalid value");
    }        
}


int main(int ac, char* av[])
{
    try {
        options_description desc("Allowed options");
        desc.add_options()
            ("help", "produce a help screen")
            ("version,v", "print the version number")
            ("magic,m", value<magic_number>(), 
                 "magic value (in NNN-NNN format)")
            ;
        
        variables_map vm;
        store(parse_command_line(ac, av, desc), vm);
   
        if (vm.count("help")) {
            cout << "Usage: regex [options]\n";
            cout << desc;
            return 0;
        }
        if (vm.count("version")) {
            cout << "Version 1.\n";
            return 0;
        }
        if (vm.count("magic")) {
            cout << "The magic is \"" 
                 << vm["magic"].as<magic_number>().n << "\"\n";
        }
    }
    catch(exception& e)
    {
        cout << e.what() << "\n";
    }    
}