c - How to convert unsigned long to string

Question

In the C language, how do I convert unsigned long value to a string (char *) and keep my source code portable or just recompile it to work on other platform (without rewriting code?

For example, if I have sprintf(buffer, format, value), how do I determine the size of buffer with platform-independent manner?

Answer 1

const int n = snprintf(NULL, 0, "%lu", ulong_value);
assert(n > 0);
char buf[n+1];
int c = snprintf(buf, n+1, "%lu", ulong_value);
assert(buf[n] == '');
assert(c == n);