CURLOPT_WRITEFUNCTION(3)

CURLOPT_WRITEFUNCTION(3curl_easy_setopt optionCURLOPT_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 prototype 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  possi-
     ble  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  ter-
     minated!

     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

libcurl 7.58.0   Last change: February 03, 2016                 1

CURLOPT_WRITEFUNCTION(3curl_easy_setopt optionCURLOPT_WRITEFUNCTION(3)

     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 7.58.0   Last change: February 03, 2016                 2