---
name: "CURLOPT_POSTFIELDSIZE"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_POSTFIELDSIZE"
---

# CURLOPT\_POSTFIELDSIZE(3)

size of POST data pointed to

## 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)](/CURLOPT_READFUNCTION/3.md)* (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)](/CURLOPT_POSTFIELDSIZE_LARGE/3.md)*.

## 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)](/curl_easy_setopt/3.md)* returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**CURLOPT\_POSTFIELDS**(3)](/CURLOPT_POSTFIELDS/3.md), [**CURLOPT\_POSTFIELDSIZE\_LARGE**(3)](/CURLOPT_POSTFIELDSIZE_LARGE/3.md)