Can someone explain the arguments to write function used for the curl option CURLOPT_WRITEFUNCTION

Question

From http://curl.haxx.se/libcurl/c/libcurl-tutorial.html:

So, you write your own function that matches this prototype:

 size_t write_data(void *buffer, size_t size, size_t nmemb, void *userp); 

You tell libcurl to pass all data to this function by issuing a function similar to this:

 curl_easy_setopt(easyhandle, CURLOPT_WRITEFUNCTION, write_data);

Can someone explain what the arguments size and nmemb stand for? Is size the number of characters in the response? Then what is nmemb?

Answer 1

This is designed for the function such as: size_t fwrite(const void* buffer, size_t size, size_t count, FILE* stream);

FILE* out = fopen("out.html", "w");
curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, (void *)out);
curl_easy_setopt(easyhandle, CURLOPT_WRITEFUNCTION, fwrite);

So we need not to add more code for fwrite as it is!

Answer 2

Apparently "size is the size of one data item, nmemb is the number of data items". My guess is that it's some internal implementation detail. The real data size = size * nmemb.

The documentation for the callback function: https://curl.haxx.se/libcurl/c/CURLOPT_WRITEFUNCTION.html

Example code:
https://github.com/curl/curl/blob/master/docs/examples/getinmemory.c