Boost::Program_options, passing an unknown command line argument - c++

Question

I am using boost::program_options to pass configuration files for my program. In particular I use often command line overriding of some of the options. For example if I register two options "opt1" and "opt2" I can successfully override the default values by running my program with
myProgram.exe --opt1=option_value_1 --opt2=option_value_2
All good, but it happened already few times that I run my program mistakenly as
myProgram.exe --opt1=option_value_1 opt2=option_value_2
In such a case (missing double hyphen) no error is thrown. In fact I can apparently run myProgram as
myProgram.exe list of any unregistered and unknown values
and it still runs correctly. I would expect to at least get informed that something unexpected happened. Is there a solution to my problem?

Answer 1

You should remove allow_unregistered() from your parse command. You command should simply be
po::store(parse_command_line(argc, argv, desc), vm);
then exception will be thrown on unknown options.
http://www.boost.org/doc/libs/1_54_0/doc/html/program_options/howto.html#idp123440592
If you want exception/error, if option has no "--" you should write extra parser, something like this, can help you
std::pair<std::string, std::string> fix_option(const std::string& value)
{
std::string name = value;
std::string val;
std::string::size_type pos = name.find("=");
if (pos != std::string::npos)
{
val = name.substr(pos + 1);
name = name.substr(0, pos);
}
if (name.substr(0, 2) != "--")
{
throw std::logic_error(std::string("invalid command, no -- in command: ") + name);
}
return std::make_pair(name.substr(2), val);
}
code example
results:
./new --help=j
output: j
./new help=j
output:
terminate called after throwing an instance of 'std::logic_error'
what(): invalid command, no -- in command: help

Answer 2

It seems that boost::program_options does not recognize positional arguments per default. This means that non-option arguments like opt2=option_value_2 are ignored. However, the documentation is not clear about it. You can enable handling of positional arguments with basic_command_line_parser::positional().
By Example
try {
po::variables_map vm;
po::store(po::command_line_parser(argc, argv).
options(desc).positional({}).run(),
vm);
po::notify(vm);
} catch (po::too_many_positional_options_error &e) {
// A positional argument like `opt2=option_value_2` was given
cerr << e.what() << endl;
exit(1);
} catch (po::error_with_option_name &e) {
// Another usage error occurred
cerr << e.what() << endl;
exit(1);
}
Explanation
Basically,
po::store(po::parse_command_line(argc, argv, desc), vm);
has been replaced with
po::store(po::command_line_parser(argc, argv)
.options(desc).positional({}).run(),
vm);
As I understand the documentation, parse_command_line(argc, argv, desc) is a shorthand for command_line_parser(argc, argv).options(desc).run(). Through adding a call to positional(), we are enabling handling of positional arguments. Through specifying {}, no positional arguments are allowed. An instance of too_many_positional_options_error is thrown when too many positional arguments are given.