Add ability to mark options as required

[GoogleCodeExporter]

There isn't currently any way to mark a flag as required for operation of the 
program. It would be nice to have a uniform way for a flag to be marked as 
required.


What version of the product are you using? On what operating system?
shflags-1.0.3.tgz, Centos 5.4 and archlinux

Original issue reported on code.google.com by BostonVaulter on 15 Jul 2010 at 3:47

[rehanog]

Yes - this would be great. Any progress?

[stephenchu]

+1000 on this feature. shflags has been great to me, and this feature is about the only thing I miss.

[raine]

👍 Maybe a sensible approach would be to have shflags complain on execution if a default value is not passed. Or alternatively introduce something like DEFINE_string_required.