Vladimir Prus wrote:

Merrill Cornish wrote:

...

graph_file is a positional parameter. So should it be added to the option_description list?

Yes, how else would you specify the type of the value? positional_options_description only specifies translation from position on the command line to option name, the option still has to be registered. I've added a warning to the docs.

I'm sure a warning will help as that's not at all obvious in the current documentation. A comment in the example would be useful too. It took me a while for the penny to drop the first time I used this library. FWIW my (now obviously erroneous) reasoning was that a positional_options_description was just another kind of options_description, and that "input-file" was in both of them in example/program_options.cpp so it could be used as both an option and a positional argument. I only wanted it as a positional parameter, so I omitted it from the options_description. I also found myself wanting to generate a usage message like this... po::positional_options_description pd; cout << "Usage: " << progname << " [options]" << pd << endl; rather than having to loop through pd. But these are minor things. Thank you for a very useful library. --- Peter Whaite.