How to detect integer overflow in C [duplicate]

Answer 1

Signed operands must be tested before the addition is performed. Here is a safe addition function with 2 comparisons in all cases:

#include 

int safe_add(int a, int b) {
    if (a >= 0) {
        if (b > INT_MAX - a) {
            /* handle overflow */
        } else {
            return a + b;
        }
    } else {
        if (b < INT_MIN - a) {
            /* handle negative overflow */
        } else {
            return a + b;
        }
    }
}

If the type long long is known to have a larger range than type int, you could use this approach, which might prove faster:

#include 

int safe_add(int a, int b) {
    long long res = (long long)a + b;
    if (res > INT_MAX || res < INT_MIN) {
        /* handle overflow */
    } else {
        return (int)res;
    }
}