Best way to detect integer overflow in C/C++
- by Chris Johnson
I was writing a program in C++ to find all solutions of a^b = c (a to the power of b), where a, b and c together use all the digits 0-9 exactly once. The program looped over values of a and b, and ran a digit-counting routine each time on a, b and a^b to check if the digits condition was satisfied.
However, spurious solutions can be generated when a^b overflows the integer limit. I ended up checking for this using code like:
unsigned long b, c, c_test;
...
c_test=c*b; // Possible overflow
if (c_test/b != c) {/* There has been an overflow*/}
else c=c_test; // No overflow
Is there a better way of testing for overflow? I know that some chips have an internal flag that is set when overflow occurs, but I've never seen it accessed through C or C++.
