Supporting unsigned int string conversions without going negative

atol_test.c

/* NOTES:
  1. On 64bit without stdlib.h included, atol and strtoul of >MAXINT 
     returns "18446744071562067968" which is ULONG_MAX-INT_MAX on 64bit
  2. On 32bit
     a. with or without stdlib, >MAXINT returns MAXINT for atol()
     b. W/wo stdlib, strtoul does the correct conversion

  SUGGESTIONS:
  1. Build for 64bit but make sure stdlib.h is included
  2. Example
        #if __WORDSIZE == 64
        # include <stdlib.h>
        #else
        # define atol(x)    strtoul(x, NULL, 10)
        # define atoi(x)    (unsigned int)strtoul(x, NULL, 10)
        #endif
*/
#include <stdio.h>
#if __WORDSIZE == 64
# include <stdlib.h>
#else
# define atol(x)    strtoul(x, NULL, 10)
# define atoi(x)    (unsigned int)strtoul(x, NULL, 10)
#endif
#include <limits.h>

#define MAXINT_STR              "2147483647"
#define MAXINT_PLUS_ONE_STR     "2147483648"
#define ULONGMAX_PLUS_ONE_STR   ""

int
main(void)
{
    unsigned int i = (unsigned int)atoi(MAXINT_PLUS_ONE_STR);
    unsigned long l = (unsigned long)atol(MAXINT_PLUS_ONE_STR);
    unsigned long sl = (unsigned long)strtoul(MAXINT_PLUS_ONE_STR, NULL, 10);
    
    printf("MAXINT: %u\n", INT_MAX);
    printf("ULONGMAX: %lu\n", ULONG_MAX);
    printf("atoi: %u\n", i);
    printf("atol: %lu\n", l);
    printf("strtoul: %lu\n", sl);

}