atoi_r.c

#include <stdio.h>      /* printf, fgets */
#include <stdlib.h>     /* atoi */
#include <string.h>

/**
  * atoi_r : a wrapper for atoi.
  * atoi from stdlib.h has undefined behaviour if input does not contain
  * a valid integer value. this function handles that undefined behaviour
  * for non negative integers.
  *
  */
int atoi_r(const char *str);

int main(int argc, char **argv){

    const char * str0 = "12312313", *str1="asd";
    
    printf("%d\n", atoi_r(str0));
    printf("%d\n", atoi_r(str1));

    return 0;
}


int atoi_r(const char *str){
    char c;

    for(size_t i = 0; i < strlen(str); ++i){
        if ('0' > str[i] || str[i] > '9')
            return -1;
    }
    return atoi(str);
}