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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)

2026-10-14 libcurl