Since curl_easy_setopt() is a vararg function where the 3rd argument can use
different types depending on the situation, normal C language type conversion
cannot be done. You must make sure that you truly pass a long and not an
int if the documentation tells you so. On architectures where they are the
same size, you may not get any problems but not all work like that. Similarly,
for options that accept a curl_off_t type, it is crucial that you pass
in an argument using that type and no other.
Enforce a long:
curl_easy_setopt(handle, CURLOPT_TIMEOUT, 5L); /* 5 seconds timeout */
Enforce a curl_off_t:
curl_off_t no_larger_than = 0x50000;
curl_easy_setopt(handle, CURLOPT_MAXFILESIZE_LARGE, no_larger_than);