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 prototype shown above.

       This  callback  function gets called by libcurl as soon as there is data received that needs to be saved.
       For most transfers, this callback gets called many times and each invoke delivers another chunk of  data.
       ptr points to the delivered data, and the size of that data is nmemb; size is always 1.

       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 function, 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),