"-fwrapv" option in gcc
"-fwrapv" option in gcc
c - What does -fwrapv do? - Stack Overflow
-fwrapv tells the compiler that overflow of signed integer arithmetic must be treated as well-defined behavior, even though it is undefined in the C standard.
It has two meaning full results:
- INT_MAX + 1 is overflowed to INT_MIN correctly. This is almost the default behavior in gcc.
- Don’t let the compiler assume
x + 1 > x.
See the program below
╭─ycz at 9f38a58b120d in /home/dev 24-08-05 - 13:28:02
╰─○ cat test.c
#include <stdio.h>
#define INT_MAX 0x7FFFFFFF
static int compare(int x) {return x + 1 > x;}
int main()
{
int x = 0;
printf("%d is bigger than %d?\n%d\n", x + 1, x, compare(x));
x = INT_MAX;
printf("%d is bigger than %d?\n%d\n", x + 1, x, compare(x));
return 0;
}
╭─ycz at 9f38a58b120d in /home/dev 24-08-05 - 13:28:06
╰─○ gcc test.c && ./a.out
1 is bigger than 0?
1
-2147483648 is bigger than 2147483647?
1
╭─ycz at 9f38a58b120d in /home/dev 24-08-05 - 13:28:13
╰─○ gcc test.c -fwrapv && ./a.out
1 is bigger than 0?
1
-2147483648 is bigger than 2147483647?
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