What's an efficient way to avoid integer overflow converting an unsigned int to int in C++?

Question

Is the following an efficient and problem free way to convert an unsigned int to an int in C++:

#include <limits.h>
void safeConvert(unsigned int passed) 
{
    int variable = static_cast<int>(passed % (INT_MAX+1)); 
    ...
}

Or is there a better way?

UPDATE

As pointed out by James McNellis it is not undefined to assign an unsigned int > INT_MAX to an integer - rather this is implementation defined. As such the context here is now specifically on my preference is to ensure this integer resets to zero when the unsigned int exceeds INT_MAX.

Original Context

I have a number of unsigned int's used as counters, but want to pass them around as integers in a specific case.

Under normal operation these counts will remain within the bounds of INT_MAX. However to avoid running into undefined implementation specific behaviour should the abnormal (but valid) case occur I want some efficient conversion here.

Answer 1

Under normal operation these counts will remain within the bounds of INT_MAX. However to avoid running into undefined behaviour should the abnormal (but valid) case occur I want some efficient conversion here.

Efficient conversion to what? If all the shared values for int and unsigned int correspond, and you want other unsigned values such as INT_MAX + 1 to each have distinct values, then you can only map them onto the negative integer values. This is done by default, and can be explicitly requested with static_cast<int>(my_unsigned). Otherwise, you could map them all to 0, or -1, or INT_MIN, or throw away the high bit... easiest way is simply: if (my_unsigned > INT_MAX) my_unsigned = XXX, or ...my_unsigned &= INT_MAX to clear the high bit. But will the called functions work properly if the int overflows? Perhaps a better solution would be to use 64-bit ints to begin with?

Answer 2

This should also work:

int variable = passed & INT_MAX;