CURLcode curl_easy_setopt(CURL *handle, CURLOPT_COPYPOSTFIELDS, char *data);
Because data are copied, care must be taken when using this option in conjunction with CURLOPT_POSTFIELDSIZE(3) or CURLOPT_POSTFIELDSIZE_LARGE(3): If the size has not been set prior to CURLOPT_COPYPOSTFIELDS(3), the data is assumed to be a null-terminated string; else the stored size informs the library about the byte count to copy. In any case, the size must not be changed after CURLOPT_COPYPOSTFIELDS(3), unless another CURLOPT_POSTFIELDS(3) or CURLOPT_COPYPOSTFIELDS(3) option is issued.
CURL *curl = curl_easy_init();
if(curl) {
char local_buffer[1024]="data to send";
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
/* size of the data to copy from the buffer and send in the request */
curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, 12L);
/* send data from the local stack */
curl_easy_setopt(curl, CURLOPT_COPYPOSTFIELDS, local_buffer);
curl_easy_perform(curl);
}