Echo在Boost中输入了命令行参数

Question

I am using boost::program_options to parse command line parameters. I would like my program to echo the entered parameters back to the user for verification. This sounds like a simple task but I was unable to find an elegant solution.

The problem is that the user can enter all sorts of data types (strings, integer, boolean values, etc...). Usually this is handled nicely by boost. But I have troubles casting the values back to strings in order to echo them back to the user.

Here is what I am currently doing

// set up program options
po::options_description optdesc("Allowed options");
optdesc.add_options()
    ("help", "Produces this help screen")
    ("opt1", po::value<string>(), "Option 1")
    ("opt2", po::value<int>(), "Option 2")
    ("opt3", po::value<bool>(), "Option 3);

// parse command line
try
{
    po::store(po::parse_command_line(argc, argv, optdesc), cmdline);
    po::notify(cmdline);
}

// do error handling ...

// echo parameters back to user
for (po::variables_map::iterator it = cmdline.begin(); it != cmdline.end(); ++it)
{
    boost::any arg = it->second.value();
    if (typeid(string) == arg.type())
    {
         cout << "  " << it->first << ":  " << boost::any_cast<string>(it->second.value()) << endl;
    }
    else if (typeid(int) == arg.type())
    {
         cout << "  " << it->first << ":  " << boost::any_cast<int>(it->second.value()) << endl;
    }
    // etc...

I really don't like this solution. Since Boost is able to convert the user input from a string to the appropiate value it should also be able to convert the value back to a string representation without me explicitly testing for the data type.

Is this possible? If yes, how can I do that.

Thanks

Answer 1

You already have argv and argc , just echo them back to the user

#include <iostream>
#include <iterator>

int
main(int argc, char* argv[])
{
    std::cout << "got " << argc << " args" << std::endl;
    std::copy(argv + 1, argv + argc, std::ostream_iterator<char*>(std::cout, " "));
    std::cout << std::endl;
}

produces

samm:stackoverflow samm$ ./a.out asdf 1 2 3 hello world
got 7 args
asdf 1 2 3 hello world 
samm:stackoverflow samm$

There's no need to iterate through the variables_map and cast each entry.

Answer 2

I faced similar problem and this is my solution. In brief you have to write your own container for options based on boost::variant, not on boots::any (on which boost::po is based). This container can be filled via notifiers of boost::po options. This will allow you to use the Visitor pattern for your options and to process them in a generic way.