longopts

Longopts refers to the array of option descriptors used with the GNU C library function getopt_long to parse long-form command-line options. The convention uses a statically defined array of struct option, often named longopts, to describe each supported option such as --help or --version beyond the traditional short options like -h. The struct and its conventions are defined in getopt.h.

Each element is a struct option, defined in getopt.h, with four fields: name (the long option string without leading dashes), has_arg (no_argument, required_argument, or optional_argument), flag (pointer to int or NULL), and val (an int value returned by getopt_long when the option is found). The array must be terminated by an element with name set to NULL. The has_arg values are typically defined as no_argument (0), required_argument (1), and optional_argument (2).

How it works: If flag is non-NULL, getopt_long assigns *flag = val and returns 0 when the option is seen; if flag is NULL, getopt_long returns val. The longindex parameter records the index of the matched element in the longopts array. The call to getopt_long also takes a string of short options. Typical pattern: while ((c = getopt_long(argc, argv, shortopts, longopts, &longindex)) != −1) { switch (c) { case 'h': ... break; case 0: // flag set; break; } }

Portability: getopt_long is a GNU extension; not all platforms support it. For portability, some projects implement their own parsing or rely on third-party libraries; POSIX clarifications exist for short options only. There is also getopt_long_only for interpreting options starting with -- by default.

Naming: longopts is a conventional name for the array; the exact identifier can be chosen by the programmer.