Checking for compatible version.

compatibe.c

#include <assert.h>

/// Check if versions are compatible.
/**
 * Compares the required and available versions and returns true iff the
 * requirement is satisfied.
 */
int compatible(unsigned r_major, unsigned r_minor, unsigned r_patch,
               unsigned a_major, unsigned a_minor, unsigned a_patch)
{
	if ( r_major == 0 )
	{
		return r_major == a_major && // For version 0 there are no compatibility
		       r_minor == a_minor && // guarantees, so if the versions are different
		       r_patch == a_patch ;  // we must assume they are not compatible.
	}
	if ( r_major != a_major ) return 0; // Available version is not backwards compatible.
	if ( r_minor >  a_minor ) return 0; // Needs features not in available version.
	
	// Don't compare minor versions, they are not relevant.
	
	return 1;
}

int main (int argc, char **argv)
{
	assert(compatible(1,2,3, 1,2,3));
	assert(compatible(0,2,3, 0,2,3));
	assert(compatible(1,2,1, 1,2,3));
	assert(compatible(1,2,5, 1,2,3));
	assert(compatible(1,2,3, 1,5,2));
	
	assert(!compatible(0,2,4, 0,2,3));
	assert(!compatible(0,3,3, 0,2,3));
	assert(!compatible(1,3,3, 1,2,3));
	assert(!compatible(1,2,3, 2,2,3));
	assert(!compatible(2,2,3, 1,2,3));
}