I'm trying to support non-conventional syntax on the form "option=value", where boolean options are given as "option=on" or "option=off". For this I've implemented a custom parser that splits a string on the '=' character and returns a std::pair<std::string, std::string> containing the option and it's value. This works fine for most things except I can't figure out how to handle boolean options. I've tried the following which just makes the option "disappear" if it's set to "off" and returns a pair with the option and an empty string as value if it's set to "on". It works for "off", but for "on" I get an exception stating "extra parameter in 'option'". Is there any way to get around this? Here's my custom parser: //---------------- START: code std::pair<std::string, std::string> custom_parser(std::string const & s) { std::pair<std::string, std::string> option; if (s.find("=") != std::string::npos) { std::vector<std::string> slist; boost::split(slist, s, boost::is_any_of("=")); if (slist[1] == "on") { option.first = slist[0]; } else if (slist[1] == "off") { // Return an empty option if the feature is turned off } else { option.first = slist[0]; option.second = slist[1]; } } return option; } //-------------- END: code Any help appreciated! Regards, -- Tarjei