parg

A small C library for parsing command-line arguments. It supports short options, long options, optional arguments, and GNU-style handling of non-option arguments.

Build

• Build the static library and example with Zig: zig build
• Run parser regression tests: zig build test
• Run the example: zig build run -- --help
• Artifacts are placed under zig-out/

Usage

• Add include/parg/parg.h and src/parg.c to your build.
• Compile src/parg.c as C (the Zig build uses -std=c23).

Example

#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>

#include "parg/parg.h"

static int parse_nonnegative_int(const char *text, int *out) {
  char *end = nullptr;
  long value;

  errno = 0;
  value = strtol(text, &end, 10);
  if (errno != 0 || end == text || *end != '\0' || value < 0 ||
      value > INT_MAX) {
    return -1;
  }

  *out = (int)value;
  return 0;
}

int main(int argc, char **argv) {
  struct parg_state ps;
  parg_init(&ps);

  const struct parg_option longopts[] = {
      {"help", PARG_NOARG, nullptr, 'h'},
      {"output", PARG_REQARG, nullptr, 'o'},
      {"size", PARG_OPTARG, nullptr, 's'},
      {nullptr, PARG_NOARG, nullptr, 0},
  };

  int size = 0;
  int opt;
  while ((opt = parg_getopt_long(&ps, argc, argv, ":ho:s::", longopts, nullptr)) != -1) {
    if (opt == 1) {
      printf("arg: %s\n", ps.optarg);
      continue;
    }

    switch (opt) {
    case 'h':
      printf("help\n");
      return 0;
    case 'o':
      printf("output=%s\n", ps.optarg);
      break;
    case 's':
      if (ps.optarg == nullptr) {
        size = 1;
        break;
      }
      if (parse_nonnegative_int(ps.optarg, &size) != 0) {
        fprintf(stderr, "Invalid size: %s\n", ps.optarg);
        return 1;
      }
      printf("size=%d\n", size);
      break;
    case '?':
      if (ps.optopt) {
        fprintf(stderr, "Unknown option: -%c\n", ps.optopt);
      } else {
        const char *token = ps.optind > 0 ? argv[ps.optind - 1] : "(unknown)";
        fprintf(stderr, "Unknown or ambiguous option: %s\n", token);
      }
      return 1;
    case ':':
      fprintf(stderr, "Missing value for option: -%c\n", ps.optopt);
      return 1;
    }
  }

  return 0;
}

API

• parg_init(struct parg_state *ps) initializes parser state.
• parg_getopt(...) parses short options.
• parg_getopt_long(...) parses short and long options.
• parg_reorder(...) reorders argv so options come first.

License

• MIT-0. See include/parg/parg.h or src/parg.c for details.