strtol not behaving as expected, c
Question
#include<limits.h>
#include<errno.h>
long output;
errno = 0;
output = strtol(input,NULL,10);
printf("long max = %ld\n",LONG_MAX);
printf("input = %s\n",input);
printf("output = %ld\n",output);
printf("direct call = %ld\n",strtol(input,NULL,10));
if(errno || output >= INT_MAX || output <= INT_MIN) {
printf("Input was out of range of int, INT_MIN = %d, INT_MAX = %d\n",INT_MIN,INT_MAX);
printf("Please input an integer within the allowed range:\n");
}
when the code above is fed with an input array of {'1','2','3','4','5','6','7','8','9','0','1'}
i get an output of:
long max = 9223372036854775807
input = 12345678901
output = -539222987
direct call = 3755744309
what is going on... strtol appears to be suffering from overflow but not setting errno
La solution
You're most likely not including the required <stdio.h>
and/or <stdlib.h>
headers.
Your code works fine (GCC in 64bit mode) once you include those:
$ cat t.c
#include<limits.h>
#include<errno.h>
#include<stdlib.h>
#include<stdio.h>
int main (void)
{
long output;
char input[] = "12345678901";
errno = 0;
output = strtol(input,NULL,10);
printf("long max = %ld\n",LONG_MAX);
printf("input = %s\n",input);
printf("output = %ld\n",output);
printf("direct call = %ld\n",strtol(input,NULL,10));
if(errno || output >= INT_MAX || output <= INT_MIN) {
printf("Input was out of range of int, INT_MIN = %d, INT_MAX = %d\n",INT_MIN,INT_MAX);
printf("Please input an integer within the allowed range:\n");
}
return 0;
}
$ gcc -Wall -Wextra -pedantic t.c
$ ./a.out
long max = 9223372036854775807
input = 12345678901
output = 12345678901
direct call = 12345678901
Input was out of range of int, INT_MIN = -2147483648, INT_MAX = 2147483647
Please input an integer within the allowed range:
BTW, you should be saving errno
right after the strtol
call, the library functions you call between strtol
and your conditional could alter its value.
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