CURLOPT_POSTFIELDSIZE(3) Library Functions Manual CURLOPT_POSTFIELDSIZE(3)
NAME
CURLOPT_POSTFIELDSIZE - size of POST data pointed to
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_POSTFIELDSIZE, long size);
DESCRIPTION
Set the size of the data buffer to POST to prevent libcurl from doing a
strlen() to figure out the data size. When this option is used you can
post fully binary data, which otherwise is likely to fail. If this size
is set to -1, libcurl uses strlen() to get the size or relies on the
CURLOPT_READFUNCTION(3) (if used) to signal the end of data.
You must make sure that the set size is not larger than the provided
buffer.
If you post more than 2GB, use CURLOPT_POSTFIELDSIZE_LARGE(3).
DEFAULT
-1
PROTOCOLS
This functionality affects http, mqtt and rtsp
EXAMPLE
#include <string.h> /* for strlen */
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
static const char *data = "data to send";
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
/* size of the POST data */
curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, (long)strlen(data));
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, data);
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.2
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_POSTFIELDS(3), CURLOPT_POSTFIELDSIZE_LARGE(3)
libcurl 2026-10-18 CURLOPT_POSTFIELDSIZE(3)
curl 8.23.0 - Generated Sun Oct 18 16:31:13 CDT 2026