CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADERDATA, void *pointer);
If CURLOPT_WRITEFUNCTION(3) or CURLOPT_HEADERFUNCTION(3) is used, pointer will be passed in to the respective callback.
If neither of those options are set, pointer must be a valid FILE * and it will be used by a plain fwrite() to write headers to.
struct my_info {
int shoesize;
char *secret;
};
static size_t header_callback(char *buffer, size_t size,
size_t nitems, void *userdata)
{
struct my_info *i = (struct my_info *)userdata;
/* now this callback can access the my_info struct */
return nitems * size;
}
CURL *curl = curl_easy_init();
if(curl) {
struct my_info my = { 10, "the cookies are in the cupboard" };
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_callback);
/* pass in custom data to the callback */
curl_easy_setopt(curl, CURLOPT_HEADERDATA, &my);
curl_easy_perform(curl);
}