What is the best way to represent arbitrarily big numbers in c?

Question

I'm working on a project that requires me to work with numbers larger than the largest numerical datatype in c. I was thinking of using structs with bit fields to represent this, but it's already smelling bad. Anyone got any tips? (Not looking for a library, more of a thought process to go behind doing something like this.)

Answer 1

The GNU MP Bignum Library would be my first choice.

Answer 2

I suggest to first check out the GNU MP Bignum library.

If licensing is a problem you have to roll your own. My first choice for the data-type would be a simple array of unsigned chars along with some extra data to denote how large that array is.

Something like this:

typedef struct 
{
  unsigned char * NumberData;
  size_t          AllocatedSize;
} MyBigNum;

Should be sufficient.