C++: Big Integers

Question

I am a writing a lexer as part of a compiler project and I need to detect if an integer is larger than what can fit in a int so I can print an error. Is there a C++ standard library for big integers that could fit this purpose?

Answer 1

The Standard C library functions for converting number strings to integers are supposed to detect numbers which are out of range, and set errno to ERANGE to indicate the problem. See here

Answer 2

You could probably use libgmp. However, I think for your purpose, it's just unnecessary.

If you, for example, parse your numbers to 32-bit unsigned int, you

1. parse the first at most 9 decimal numbers (that's floor(32*log(2)/log(10)). If you haven't more, the number is OK.
2. take the next digit. If the number you got / 10 is not equal to the number from the previous step, the number is bad.
3. if you have more digits (eg. more than 9+1), the number is bad.
4. else the number is good.

Be sure to skip any leading zeros etc.