I struggled to find good documentation for implementing a command line program option using boost which supports the following behaviors:
./test
./test -t
./test -t explicit
That is, a default value, an "implicit value" and an explicit value. The ./test -t case was giving me trouble and I was getting runtime errors like:
.main(65770) malloc: *** error for object 0x7fff77545860: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
#4 0x00000001002a4313 in std::_Rb_tree<std::string, std::pair<std::string const, std::string>, std::_Select1st<std::pair<std::string const, std::string> >, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > >::_M_erase (this=0x7fff5fbfe398, __x=0x10705f650) at basic_string.h:246
Turns out this is possible using the implicit_value() function. Here's a small example:
#include <iostream>
#include <boost/program_options.hpp>
int main(int argc, char * argv[])
{
using namespace std;
string test;
namespace po = boost::program_options;
po::options_description desc("Options");
desc.add_options()("test,t",
po::value<string>(&test)->
default_value("default")->
implicit_value("implicit"),
"test option, followed by string");
try
{
po::variables_map vm;
po::store(po::parse_command_line(argc, argv,desc), vm);
po::notify(vm);
}catch(const exception & e)
{
cerr << e.what() << endl << endl;
cout << desc << endl;
return 1;
}
cout<<"test: "<<test<<endl;
}
Running ./test produces test: default, ./test -t or ./test --test produces test: implicit, and ./test -texplicit, ./test -t explicit, ./test --test=explicit, or ./test --test explicit produces test: explicit.