How to solve "boost::bad_any_cast: failed conversion using boost::any_cast" when using boost program options?
You see the boost::bad_any_cast
exception thrown from the po::variables_map
because the two const char*
argument overload of po::options_description_easy_init::operator()
does not specify a po::value_semantic
type, so converting it to a std::string
will not work. If you want to convert the value to a std::string
, and it is required for your application, use the required()
value semantic.
#include <boost/program_options.hpp>
namespace po = boost::program_options;
int main (int argc, char *argv[])
{
po::options_description config("Configuration");
config.add_options()
("IPAddress,i", po::value<std::string>()->required(), "IP Address")
("Port,p", po::value<std::string>()->required(), "Port")
;
try {
po::variables_map vm;
po::store(po::parse_command_line(argc, argv, config),vm);
po::notify(vm);
std::cout << "Values" << std::endl;
const std::string address = vm["IPAddress"].as<std::string>();
const std::string port = vm["Port"].as<std::string>();
std::cout << "address: " << address << std::endl;
std::cout << "port: " << port << std::endl;
} catch ( const std::exception& e ) {
std::cerr << e.what() << std::endl;
return 1;
}
return 0;
}
Note the added catch block since parsing can (and will, as you have noticed) throw exceptions. Here is a sample session:
samm$ ./a.out
the option '--IPAddress' is required but missing
samm$ ./a.out --IPAddress 127.0.0.1
the option '--Port' is required but missing
samm$ ./a.out --IPAddress 127.0.0.1 --Port 5000
Values
address: 127.0.0.1
port: 5000
samm$
Here is an online demo showing the same behavior, courtesy of COmpile LInk RUn (coliru).
You need to declare the ip-address and port as strings when you add the options:
config.add_options()
("IPAddress,i", po::value<std::string>(), "IP Address")
("Port,p", po::value<std::string>(), "Port")
;
This same message can also occur if you are not handling optional arguments correctly.
Sam's solution nails required arguments and the OP's code suggests required - just mark them required. For optional inputs, the Boost PO tutorial gives us a template for checking if the option exists before converting it:
if(vm.count("address"))
{
const std::string address = vm["IPAddress"].as<std::string>();
std::cout << "address: " << address << std::endl;
}
if(vm.count("port"))
const std::string port = vm["Port"].as<std::string>();
std::cout << "port: " << port << std::endl;
}
My problem - I had copied/pasted and forgotten to align the if test with the usage!