CURLOPT_POSTFIELDSIZE(3) Introduction to Library Functions

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

If you want to post static data to the server without having libcurl
do a strlen() to measure the data size, this option must be used.
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.

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) {
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);

curl_easy_perform(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 2026-01-08 CURLOPT_POSTFIELDSIZE(3)