CURLOPT_POSTFIELDS explained

Name

CURLOPT_POSTFIELDS - data to POST to server

Synopsis

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_POSTFIELDS, char *postdata);

Description

Pass a char * as parameter, pointing to the full data to send in an HTTP POST operation. You must make sure that the data is formatted the way you want the server to receive it. libcurl will not convert or encode it for you in any way. For example, the web server may assume that this data is URL encoded.

The data pointed to is NOT copied by the library: as a consequence, it must be preserved by the calling application until the associated transfer finishes. This behavior can be changed (so libcurl does copy the data) by setting the CURLOPT_COPYPOSTFIELDS option.

This POST is a normal application/x-www-form-urlencoded kind (and libcurl will set that Content-Type by default when this option is used), which is commonly used by HTML forms. Change Content-Type with CURLOPT_HTTPHEADER.

You can use curl_easy_escape to URL encode your data, if necessary. It returns a pointer to an encoded string that can be passed as postdata.

Using CURLOPT_POSTFIELDS implies setting CURLOPT_POST to 1.

If CURLOPT_POSTFIELDS is explicitly set to NULL then libcurl will get the POST data from the read callback. If you want to send a zero-byte POST set CURLOPT_POSTFIELDS to an empty string, or set CURLOPT_POST to 1 and CURLOPT_POSTFIELDSIZE to 0.

libcurl will use assume this option points to a null-terminated string unless you also set CURLOPT_POSTFIELDSIZE to specify the length of the provided data, which then is strictly required if you want to send off null bytes included in the data.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header, and libcurl will add that header automatically if the POST is either known to be larger than 1MB or if the expected size is unknown. You can disable this header with CURLOPT_HTTPHEADER as usual.

To make multipart/formdata posts, check out the CURLOPT_MIMEPOST option combined with curl_mime_init.

Default

NULL

Protocols

HTTP

Example

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, 12L);
 
  /* pass in a pointer to the data - libcurl will not copy */
  curl_easy_setopt(curl, CURLOPT_POSTFIELDS, data);
 
  curl_easy_perform(curl);
}

Availability

Always

Return value

Returns CURLE_OK