Replace `?` key with `h` key in GNU argp...

Cannot parse flag with argument in argp.h...

C argp : Handle option require...

GNU argp: How to parse option with only long name?...

getopt usage with/without option...

What's the difference between argp and getopt?...

C - how to allow unrecognized options in Argp or Getopt?...

How to accept a char or string as input...