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* Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
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CURLINFO_CONTENT_LENGTH_DOWNLOAD_T - get content-length of download #include <curl/curl.h> CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_CONTENT_LENGTH_DOWNLOAD_T, curl_off_t *content_length); Pass a pointer to a curl_off_t to receive the content-length of the download. This is the value read from the Content-Length: field. Stores -1 if the size isn't known. HTTP(S)

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

 /* Perform the request */
 res = curl_easy_perform(curl);

 if(!res) {
 /* check the size */
 curl_off_t cl;
 res = curl_easy_getinfo(curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD_T, &cl);
 if(!res) {
 printf("Download size: %" CURL_FORMAT_CURL_OFF_T "\\n", cl);
 }
 }
}

Added in 7.55.0 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not. curl_easy_getinfo "(3), " curl_easy_setopt "(3), " CURLINFO_CONTENT_LENGTH_UPLOAD_T "(3), "