Simple C flag parser using uthash. http://troydhanson.github.com/uthash/

flags.c

#include "flags.h"

#define isopt(text) strncmp(text, "--", 2) == 0
#define isneg(text) strncmp(text, "--no-", 4) == 0

flags_t *flags_parse(int argc, char *argv[]) {
  int n;
  char *option, *value;
  flags_t *flags = NULL, *flag;

  for (n = 0, option = argv[0]; n < argc; n++, option = argv[n]) {
    if (!isopt(option)) continue;

    flag = (flags_t *)malloc(sizeof(flags_t));
    if (isneg(option)) { // negation, always boolean
      flag->option = option + 5;
      flag->value  = "false";
    }
    else if ((value = strchr(option, '='))) {
      *value = 0;
      flag->option = option + 2;
      flag->value  = value + 1;
    }
    else if (n < argc - 1) {
      if (isopt(argv[n + 1])) {
        flag->option = option + 2;
        flag->value  = "true";
      }
      else {
        flag->option = option + 2;
        flag->value  = argv[n + 1];
        n++;
      }
    }
    else { // last one, so booleanish
      flag->option = option + 2;
      flag->value  = "true";
    }
    HASH_ADD_KEYPTR(hh, flags, flag->option, strlen(flag->option), flag);
  }

  return flags;
}

char *flags_value(const flags_t *flags, const char *option) {
  flags_t *flag;
  HASH_FIND_STR(flags, option, flag);
  return flag ? flag->value : NULL;
}

void flags_destroy(flags_t *flags) {
  flags_t *flag, *tmp;
  HASH_ITER(hh, flags, flag, tmp) {
    HASH_DEL(flags, flag);
    free(flag);
  }
}

flags.h

#ifndef _FLAGS_H_
#define _FLAGS_H_

#include <string.h>
#include <stdlib.h>

#include "uthash.h"

typedef struct {
  char *option; // Key.
  char *value;
  UT_hash_handle hh;
} flags_t;

flags_t *flags_parse(int argc, char *argv[]);
char *flags_value(const flags_t *flags, const char *option);
void flags_destory(flags_t *flags);

#endif

usage.c

#include <stdio.h>
#include "flags.h"

int main(int argc, char *argv[]) {
  // Parse all flags.
  flags_t *flags = flags_parse(argc, argv);

  /*
    Print test flag value.
    --test         #=> "test: true"
    --test=true    #=> "test: true"
    --no-test      #=> "test: false"
    --test=false   #=> "test: false"
    --test="hello" #=> "test: hello"
  */
  printf("test: %s\n", flags_value("test"));

  flags_destroy(flags);
  return 0;
}