Very useful to me, thanks! I'm guessing that the implicit_value is distinct from the default_value, so that the default can be set seperately if the option is completely absent from the command line? My worry would be explaining the different command line syntax for applications with this type of option to my users, but I understand why it is necessary. Vladimir, will you be merging this? Does it need to be posted to the developers list instead? Steven Bryan Green wrote:
Attached is a patch to program_options that implements optional argument support, in the style of GNU getopt_long. It adds one new method to 'value_type': 'implicit_value()'. The idea is that, if the option is given without an argument, it is assigned an "implicit" value. Otherwise, if the long-option is given an explicit argument via the equals sign (--arg=value), or the short-option is given an adjacent argument (-avalue), the explicit value will override the implicit one.
For example: desc.add_options() ("proxy,p", value<int>(&proxy_port)->implicit_value(DefaultProxyPort), "run proxy service") ; ... if (vm.count("proxy")) enable_the_proxy(proxy_port);
./prog --proxy --opt2 --opt3 -> enables proxy on default port. ./prog --proxy=9000 --opt2 --opt3 -> enables proxy on port 9000. ./prog --opt2 --opt3 -> does not enable the proxy.
-Bryan
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