How to detect integer overflow in C/C++?

The only safe way is to check before the overflow occurs. There are some informal ways to check for integer overflow though. So, if your goal is to detect overflow when adding unsigned integers, you can check whether the result is actually smaller than the two added values. For example ,

Example code

unsigned int x, y;
unsigned int value = x + y;
bool overflow = value < x; // Alternatively "value < y" should also work

This is because if x and y are both unsigned integers, if they overflow after addition, their values ​​cannot be greater than one of them Either, since they need to be larger than the largest possible unsigned integer to get around and over those values.

Another approach is to try to access the overflow flag in the CPU. Some compilers provide access to it so you can test it, but it's not standard.

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