xref: /aosp_15_r20/external/curl/docs/libcurl/opts/CURLOPT_POSTFIELDS.md (revision 6236dae45794135f37c4eb022389c904c8b0090d)

---
c: Copyright (C) Daniel Stenberg, <[email protected]>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_POSTFIELDS
Section: 3
Source: libcurl
See-also:
  - CURLOPT_COPYPOSTFIELDS (3)
  - CURLOPT_MIMEPOST (3)
  - CURLOPT_POSTFIELDSIZE (3)
  - CURLOPT_READFUNCTION (3)
  - CURLOPT_UPLOAD (3)
Protocol:
  - HTTP
  - MQTT
Added-in: 7.1
---

# NAME

CURLOPT_POSTFIELDS - data to POST to server

# SYNOPSIS

~~~c
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_POSTFIELDS, char *postdata);
~~~

# DESCRIPTION

Pass a char pointer as parameter, pointing to the data buffer to use in an
HTTP POST operation or an MQTT subscribe. The data must be formatted and
encoded the way you want the server to receive it. libcurl does not convert or
encode it in any way. For example, a 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 instead using
the CURLOPT_COPYPOSTFIELDS(3) option.

This POST is a normal **application/x-www-form-urlencoded** kind (and libcurl
sets that Content-Type by default when this option is used), which is commonly
used by HTML forms. Change Content-Type with CURLOPT_HTTPHEADER(3).

You can use curl_easy_escape(3) to URL encode your data, if
necessary. It returns a pointer to an encoded string that can be passed as
*postdata*.

Using CURLOPT_POSTFIELDS(3) implies setting CURLOPT_POST(3) to 1.

If CURLOPT_POSTFIELDS(3) is explicitly set to NULL then libcurl gets the POST
data from the read callback. To send a zero-length (empty) POST, set
CURLOPT_POSTFIELDS(3) to an empty string, or set CURLOPT_POST(3) to 1 and
CURLOPT_POSTFIELDSIZE(3) to 0.

libcurl assumes this option points to a null-terminated string unless you also
set CURLOPT_POSTFIELDSIZE(3) 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 adds 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(3) as usual.

To make **multipart/formdata** posts, check out the
CURLOPT_MIMEPOST(3) option combined with curl_mime_init(3).

Using this option multiple times makes the last set pointer override the
previous ones. Set it to NULL to disable its use again.

# DEFAULT

NULL

# %PROTOCOLS%

# EXAMPLE

~~~c
/* send an application/x-www-form-urlencoded POST */
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 if strlen() is not good enough */
    curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, 12L);

    /* pass in a pointer to the data - libcurl does not copy */
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, data);

    curl_easy_perform(curl);
  }

  /* send an application/json POST */
  curl = curl_easy_init();
  if(curl) {
    const char *json = "{\"name\": \"daniel\"}";
    struct curl_slist *slist1 = NULL;
    slist1 = curl_slist_append(slist1, "Content-Type: application/json");
    slist1 = curl_slist_append(slist1, "Accept: application/json");

    /* set custom headers */
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, slist1);

    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

    /* pass in a pointer to the data - libcurl does not copy */
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json);

    curl_easy_perform(curl);
  }
}
~~~

# %AVAILABILITY%

# RETURN VALUE

Returns CURLE_OK