Question

I have an array of unsigned chars in c I am trying to print in base 10, and I am stuck. I think this will be better explained in code, so, given:

unsigned char n[3];
char[0] = 1;
char[1] = 2;
char[2] = 3;

I would like to print 197121.

This is trivial with small base 256 arrays. One can simply 1 * 256 ^ 0 + 2 * 256 ^ 1 + 3 * 256 ^ 2.

However, if my array was 100 bytes large, then this quickly becomes a problem. There is no integral type in C that is 100 bytes large, which is why I’m storing numbers in unsigned char arrays to begin with.

How am I supposed to efficiently print this number out in base 10?

I am a bit lost.

Answer 1

There’s no easy way to do it using only the standard C library. You’ll either have to write the function yourself (not recommended), or use an external library such as GMP.

For example, using GMP, you could do:

unsigned char n[100];  // number to print

mpz_t num;
mpz_import(num, 100, -1, 1, 0, 0, n);  // convert byte array into GMP format
mpz_out_str(stdout, 10, num);  // print num to stdout in base 10
mpz_clear(num);  // free memory for num