3 ms·

Is there any reason this is not written as `switch(..) { <case statements>; default: <else statements> }`. I.e is there a reason for `if(0)`?

• jsmith45 4y ago
  The whole `if` portion is for if the second character of the argument (after the initial `-`) is a second `-` [0]. In that case, the switch jumped to `case '-':` hidden within the macro, and the if statement is about processing long arguments (like `--help`). arguments only available as a short flag should never get executed as part of a short flag, so putting them inside the if(0) case is an easy option. An alternative without if(0) of any variety would be: ARG_BEGIN { if (ARG_LONG("reverse")) case 'r': { reverse = 1; ARG_FLAG(); } else if (ARG_LONG("input")) case 'i': { input = ARG_VAL(); } else if (ARG_LONG("output")) case 'o': { output = ARG_VAL(); } else if (ARG_LONG("help")) case 'h': case '?': { printf("Usage: %s [OPTION...] [STRING...]\n", argv0); puts("Example usage of arg.h\n"); puts("Options:"); puts(" -a, set a to true"); puts(" -b, set a to true"); puts(" -c, set a to true"); puts(" -r, --reverse set reverse to true"); puts(" -i, --input=STR set input string to STR"); puts(" -o, --output=STR set output string to STR"); puts(" -h, --help display this help and exit"); return EXIT_SUCCESS; } else { default: fprintf(stderr, "%s: invalid option '%s'\n" "Try '%s --help' for more information.\n", argv0, *argv, argv0); return EXIT_FAILURE; } break; case 'a': a = 1; ARG_FLAG(); break; case 'b': b = 1; ARG_FLAG(); break; case 'c': c = 1; ARG_FLAG(); break; case '\0': readstdin = 1; break; } ARG_END; The downside is that those few short flag only arguments no longer line up nicely with the others, and they come after the default, which could be a little bit confusing. Footnote: [0] Except if that second dash is the last character of the argument, in which case -- is the end of flags marker, meaning any further arguments that begin with `-` are just funky positional paramaters