CURL C API: callback was not called - c++

Question

The code below is a test for the CURL C API . The problem is that the callback function write_callback is never called. Why ?
/** compilation: g++ source.cpp -lcurl */
#include <assert.h>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <curl/curl.h>
using namespace std;
static size_t write_callback(void *ptr, size_t size, size_t nmemb, void *userp)
{
std::cerr << "CALLBACK WAS CALLED" << endl;
exit(-1);
return size*nmemb;
}
static void test_curl()
{
int any_data=1;
CURLM* multi_handle=NULL;
CURL* handle_curl = ::curl_easy_init();
assert(handle_curl!=NULL);
::curl_easy_setopt(handle_curl, CURLOPT_URL, "http://en.wikipedia.org/wiki/Main_Page");
::curl_easy_setopt(handle_curl, CURLOPT_WRITEDATA, &any_data);
::curl_easy_setopt(handle_curl, CURLOPT_VERBOSE, 1);
::curl_easy_setopt(handle_curl, CURLOPT_WRITEFUNCTION, write_callback);
::curl_easy_setopt(handle_curl, CURLOPT_USERAGENT, "libcurl-agent/1.0");
multi_handle = ::curl_multi_init();
assert(multi_handle!=NULL);
::curl_multi_add_handle(multi_handle, handle_curl);
int still_running=0;
/* lets start the fetch */
while(::curl_multi_perform(multi_handle, &still_running) ==
CURLM_CALL_MULTI_PERFORM );
std::cerr << "End of curl_multi_perform."<< endl;
//cleanup should go here
::exit(EXIT_SUCCESS);
}
int main(int argc,char** argv)
{
test_curl();
return 0;
}
Many thanks
Pierre

Answer 1

You need to check the value of still_running and call curl_multi_perform() again if there are still pending operations.
Simple example:
int still_running=0;
/* lets start the fetch */
do {
while(::curl_multi_perform(multi_handle, &still_running) ==
CURLM_CALL_MULTI_PERFORM);
} while (still_running);