C: character string to uint16_t conversion (see http://stackoverflow.com/q/20019786/1688185)

port.c

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h> /* strtoumax */
#include <stdbool.h>
#include <errno.h>

static bool str_to_uint16(const char *str, uint16_t *res);

int
main(int argc, char *argv[])
{
  if (argc != 2) {
    fprintf(stderr, "usage: %s <port>\n", argv[0]);
    exit(1);
  }

  uint16_t port;
  if (!str_to_uint16(argv[1], &port)) {
    fprintf(stderr, "conversion error\n");
    exit(2);
  }

  printf("port: %" PRIu16 "\n", port);

  return 0;
}

static bool
str_to_uint16(const char *str, uint16_t *res)
{
  char *end;
  errno = 0;
  intmax_t val = strtoimax(str, &end, 10);
  if (errno == ERANGE || val < 0 || val > UINT16_MAX || end == str || *end != '\0')
    return false;
  *res = (uint16_t) val;
  return true;
}