CURLOPT_WRITEFUNCTION - set callback for writing received data
size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);
Pass a pointer to your callback function, which should match the prototype shown
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
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
bytes of header data passed into it. This usually
This function may be called with zero bytes data if the transferred file is
The data passed to this function will not be zero terminated!
Set the userdata
argument with the CURLOPT_WRITEDATA(3)
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)
libcurl will use 'fwrite' as a callback by default.
For all protocols
Support for the CURL_WRITEFUNC_PAUSE return code was added in version 7.18.0.
This will return CURLE_OK.
A common technique is to use this callback to store the incoming data into a
dynamically growing allocated buffer. Like in the getinmemory example: