CURLOPT_WRITEDATA - pointer passed to the write callback

Added in curl 7.9.7

stdout

A data pointer to pass to the write callback. If you use the CURLOPT_WRITEFUNCTION(3) option, this is the pointer you get in that callback's fourth and last argument. If you do not use a write callback, you must make pointer a 'FILE '(castto'void ') as libcurl passes this to fwrite(3) when writing data. The internal CURLOPT_WRITEFUNCTION(3) writes the data to the FILE * given with this option, or to stdout if this option has not been set. If you are using libcurl as a Windows DLL, you MUST use a CURLOPT_WRITEFUNCTION(3) if you set this option or you might experience crashes.

A common technique is to use the write callback to store the incoming data into a dynamically growing allocated buffer, and then this CURLOPT_WRITEDATA(3) is used to point to a struct or the buffer to store data in. Like in the getinmemory example: https://curl.se/libcurl/c/getinmemory.html

This option was formerly known as CURLOPT_FILE, the name CURLOPT_WRITEDATA(3) was added in 7.9.7.

CURLOPT_WRITEDATA - pointer passed to the write callback

This functionality affects all supported protocols

This returns CURLE_OK.

CURLOPT_HEADERDATA(3), CURLOPT_READDATA(3), CURLOPT_WRITEFUNCTION(3) libcurl 2025-06-16 CURLOPT_WRITEDATA(3)

#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEDATA, void *pointer);