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CURLOPT_TIMECONDITION - select condition for a time request #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TIMECONDITION, long cond); Pass a long as parameter. This defines how the CURLOPT_TIMEVALUE(3) time value is treated. You can set this parameter to CURL_TIMECOND_IFMODSINCE or CURL_TIMECOND_IFUNMODSINCE. The last modification time of a file is not always known and in such instances this feature will have no effect even if the given time condition would not have been met. curl_easy_getinfo(3) with the CURLINFO_CONDITION_UNMET option can be used after a transfer to learn if a zero-byte successful "transfer" was due to this condition not matching. CURL_TIMECOND_NONE (0) HTTP, FTP, RTSP, and FILE

CURL *curl = curl_easy_init();
if(curl) {
 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

 /* January 1, 2020 is 1577833200 */
 curl_easy_setopt(curl, CURLOPT_TIMEVALUE, 1577833200L);

 /* If-Modified-Since the above time stamp */
 curl_easy_setopt(curl, CURLOPT_TIMECONDITION, CURL_TIMECOND_IFMODSINCE);

 /* Perform the request */
 curl_easy_perform(curl);
}

Always Returns CURLE_OK CURLOPT_TIMEVALUE "(3), "