getopt.h

[Ank1taS]

Use of getopt.h header. refer to this
getopt() is used to parse command-line arguments.
please discuss more for help

[chandrakant100]

The getopt() function is a builtin function in C and is used to parse command line arguments.

getopt(int argc, char *const argv[], const char *optstring)

`optstring` is simply  a list of characters, 
each representing a single character option.

Return Value: The getopt() function returns different values:

• If the option takes a value, that value is pointerto the external variable optarg.
• -1 if there are no more options to process.
• ?when there is an unrecognized option and it stores into external variable optopt.
• If an option requires a value (such as -f in our example) and no value is given, getopt normally returns ?.
  By placing a colon as the first character of the options string, getopt returns: instead of ? when no value is given.

src -> link.
credits: geeksforgeeks

[Ank1taS]

RETURN VALUE

• The getopt() function shall return the next option character specified on the command line.
• A colon ( ':' ) shall be returned if getopt() detects a missing argument and the first character of optstring was a colon ( ':' ).
• A question mark ( '?' ) shall be returned if getopt() encounters an option character, not in optstring or detects a missing argument and the first character of optstring was not a colon ( ':' ).
• Otherwise, getopt() shall return -1 when all command-line options are parsed.

https://pubs.opengroup.org/onlinepubs/009696799/functions/getopt.html