Parse an int range parameter

#include <stdio.h>
#include <string.h>

/**
 * If str is of the form "<m>:<n>",
 * set *min = m
 * and *max = n. Otherwise,
 * if str if of the form "<n>",
 * set *min = defaultMin and
 * *max = n.
 * Return the number of numbers
 * successfully parsed (1 or 2 indicating success,
 * 0 failure).
 */
int charToIntRange(const char* str,
     int defaultMin,
     int* min,
     int* max)
{
  if (strchr(str, ':')) {
    if (sscanf(str, "%d:%d", min, max) == 2) {
      return 2;
    }
    else {
      return 0;
    }
  }
  else {
    *min = defaultMin;
    return sscanf(str, "%d", max);
  }
}

int main(int numArgs, char** args)
{
  int i;
  for (i = 1; i < numArgs; ++i) {
    int m;
    int n;
    if (charToIntRange(args[i], -1666, &m, &n)) {
      printf("%d:%d\n", m, n);
    }
    else {
      printf("failed to parse <<%s>>\n", args[i]);
    }
  }

  return 0;
}

$ gcc -Wall charToIntRange.c
$ ./a.out 1 155:7 -3:3 :1 1: 19:-1 19:1a t15:5
-1666:1
155:7
-3:3
failed to parse <<:1>>
failed to parse <<1:>>
19:-1
19:1
failed to parse <<t15:5>>


It should probably fail with an input of "19:1a", but I'll leave off worrying about that for now.

Is the format "%[:]" portable?