Don’t call strlen more than once per string.
int EndsWith(const char *str, const char *suffix)
{
if (!str || !suffix)
return 0;
size_t lenstr = strlen(str);
size_t lensuffix = strlen(suffix);
if (lensuffix > lenstr)
return 0;
return strncmp(str + lenstr - lensuffix, suffix, lensuffix) == 0;
}
int EndsWithFoo(const char *str) { return EndsWith(str, ".foo"); }
EDIT: added NULL check for the pedantic. For the ultra pedantic, debate whether it should return non-zero if both str and suffix are both NULL.