Required and Optional Arguments Using Boost Library Program Options
Here is complete program as per rcollyer and Tim, whom the credits go to:
#include <boost/program_options.hpp>
#include <iostream>
#include <sstream>
namespace po = boost::program_options;
bool process_command_line(int argc, char** argv,
std::string& host,
std::string& port,
std::string& configDir)
{
int iport;
try
{
po::options_description desc("Program Usage", 1024, 512);
desc.add_options()
("help", "produce help message")
("host,h", po::value<std::string>(&host)->required(), "set the host server")
("port,p", po::value<int>(&iport)->required(), "set the server port")
("config,c", po::value<std::string>(&configDir)->required(), "set the config path")
;
po::variables_map vm;
po::store(po::parse_command_line(argc, argv, desc), vm);
if (vm.count("help"))
{
std::cout << desc << "\n";
return false;
}
// There must be an easy way to handle the relationship between the
// option "help" and "host"-"port"-"config"
// Yes, the magic is putting the po::notify after "help" option check
po::notify(vm);
}
catch(std::exception& e)
{
std::cerr << "Error: " << e.what() << "\n";
return false;
}
catch(...)
{
std::cerr << "Unknown error!" << "\n";
return false;
}
std::stringstream ss;
ss << iport;
port = ss.str();
return true;
}
int main(int argc, char** argv)
{
std::string host;
std::string port;
std::string configDir;
bool result = process_command_line(argc, argv, host, port, configDir);
if (!result)
return 1;
// else
std::cout << "host:\t" << host << "\n";
std::cout << "port:\t" << port << "\n";
std::cout << "config:\t" << configDir << "\n";
// Do the main routine here
}
/* Sample output:
C:\Debug>boost.exe --help
Program Usage:
--help produce help message
-h [ --host ] arg set the host server
-p [ --port ] arg set the server port
-c [ --config ] arg set the config path
C:\Debug>boost.exe
Error: missing required option config
C:\Debug>boost.exe --host localhost
Error: missing required option config
C:\Debug>boost.exe --config .
Error: missing required option host
C:\Debug>boost.exe --config . --help
Program Usage:
--help produce help message
-h [ --host ] arg set the host server
-p [ --port ] arg set the server port
-c [ --config ] arg set the config path
C:\Debug>boost.exe --host 127.0.0.1 --port 31528 --config .
host: 127.0.0.1
port: 31528
config: .
C:\Debug>boost.exe -h 127.0.0.1 -p 31528 -c .
host: 127.0.0.1
port: 31528
config: .
*/
I've run into this issue myself. The key to a solution is that the function po::store
populates the variables_map
while po::notify
raises any errors encountered, so vm
can be used prior to any notifications being sent.
So, as per Tim, set each option to required, as desired, but run po::notify(vm)
after you've dealt with the help option. This way it will exit without any exceptions thrown. Now, with the options set to required, a missing option will cause a required_option
exception to be thrown and using its get_option_name
method you can reduce your error code to a relatively simple catch
block.
As an additional note, your option variables are set directly via the po::value< -type- >( &var_name )
mechanism, so you don't have to access them through vm["opt_name"].as< -type- >()
.
A code example is provided in Peters answer