CURLOPT_WRITEFUNCTION(3)   curl_easy_setopt options   CURLOPT_WRITEFUNCTION(3)

NAME
       CURLOPT_WRITEFUNCTION - set callback for writing received data

SYNOPSIS
       #include <curl/curl.h>

       size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);

DESCRIPTION
       Pass a pointer to your callback function, which should match the proto-
       type shown above.

       This callback function gets called by libcurl as soon as there is  data
       received that needs to be saved.  ptr points to the delivered data, and
       the size of that data is size multiplied with nmemb.

       The callback function will be passed as much data as  possible  in  all
       invokes,  but you must not make any assumptions. It may be one byte, it
       may be thousands. The maximum amount of body data that will  be  passed
       to   the   write  callback  is  defined  in  the  curl.h  header  file:
       CURL_MAX_WRITE_SIZE (the usual default is 16K). If CURLOPT_HEADER(3) is
       enabled,  which makes header data get passed to the write callback, you
       can get up to CURL_MAX_HTTP_HEADER bytes of header data passed into it.
       This usually means 100K.

       This  function  may  be  called with zero bytes data if the transferred
       file is empty.

       The data passed to this function will not be zero terminated!

       Set the userdata argument with the CURLOPT_WRITEDATA(3) option.

       Your callback should return the number of bytes actually taken care of.
       If  that  amount  differs from the amount passed to your callback func-
       tion, it'll signal an error condition to the library. This  will  cause
       the  transfer  to get aborted and the libcurl function used will return
       CURLE_WRITE_ERROR.

       If your callback function returns CURL_WRITEFUNC_PAUSE  it  will  cause
       this  transfer  to  become  paused.  See curl_easy_pause(3) for further
       details.

       Set this option to NULL to  get  the  internal  default  function  used
       instead  of your callback. The internal default function will write the
       data to the FILE * given with CURLOPT_WRITEDATA(3).

DEFAULT
       libcurl will use 'fwrite' as a callback by default.

PROTOCOLS
       For all protocols

AVAILABILITY
       Support for the CURL_WRITEFUNC_PAUSE return code was added  in  version
       7.18.0.

RETURN VALUE
       This will return CURLE_OK.

EXAMPLE
       A  common  technique is to use this callback to store the incoming data
       into a dynamically growing allocated buffer. Like  in  the  getinmemory
       example: https://curl.haxx.se/libcurl/c/getinmemory.html

SEE ALSO
       CURLOPT_WRITEDATA(3), CURLOPT_READFUNCTION(3),

libcurl 7.54.0                 February 03, 2016      CURLOPT_WRITEFUNCTION(3)