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libcurl multi interface example
/* curl_multi_test.c
Clemens Gruber, 2013
Code description:
Requests 4 Web pages via the CURL multi interface
and checks if the HTTP status code is 200.
Update: Fixed! The check for !numfds was the problem.
#include <stdio.h>
#include <stdlib.h>
#ifndef WIN32
#include <unistd.h>
#include <curl/multi.h>
#define MAX_WAIT_MSECS 30*1000 /* Wait max. 30 seconds */
static const char *urls[] = {
#define CNT 4
static size_t cb(char *d, size_t n, size_t l, void *p)
/* take care of the data here, ignored in this example */
return n*l;
static void init(CURLM *cm, int i)
CURL *eh = curl_easy_init();
curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, cb);
curl_easy_setopt(eh, CURLOPT_HEADER, 0L);
curl_easy_setopt(eh, CURLOPT_URL, urls[i]);
curl_easy_setopt(eh, CURLOPT_PRIVATE, urls[i]);
curl_easy_setopt(eh, CURLOPT_VERBOSE, 0L);
curl_multi_add_handle(cm, eh);
int main(void)
CURLMsg *msg=NULL;
CURLcode return_code=0;
int still_running=0, i=0, msgs_left=0;
int http_status_code;
const char *szUrl;
cm = curl_multi_init();
for (i = 0; i < CNT; ++i) {
init(cm, i);
curl_multi_perform(cm, &still_running);
do {
int numfds=0;
int res = curl_multi_wait(cm, NULL, 0, MAX_WAIT_MSECS, &numfds);
if(res != CURLM_OK) {
fprintf(stderr, "error: curl_multi_wait() returned %d\n", res);
if(!numfds) {
fprintf(stderr, "error: curl_multi_wait() numfds=%d\n", numfds);
curl_multi_perform(cm, &still_running);
} while(still_running);
while ((msg = curl_multi_info_read(cm, &msgs_left))) {
if (msg->msg == CURLMSG_DONE) {
eh = msg->easy_handle;
return_code = msg->data.result;
if(return_code!=CURLE_OK) {
fprintf(stderr, "CURL error code: %d\n", msg->data.result);
// Get HTTP status code
szUrl = NULL;
curl_easy_getinfo(eh, CURLINFO_RESPONSE_CODE, &http_status_code);
curl_easy_getinfo(eh, CURLINFO_PRIVATE, &szUrl);
if(http_status_code==200) {
printf("200 OK for %s\n", szUrl);
} else {
fprintf(stderr, "GET of %s returned http status code %d\n", szUrl, http_status_code);
curl_multi_remove_handle(cm, eh);
else {
fprintf(stderr, "error: after curl_multi_info_read(), CURLMsg=%d\n", msg->msg);
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jdolan commented Dec 23, 2014

THANK YOU. This is so much better than the older examples found on the libcurl website that calculate timeout and issue their own select. curl_multi_wait FTW.

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smart--petea commented Aug 13, 2015

Thank you.

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chideat commented Nov 4, 2015


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iamritpal commented Jan 23, 2016

Excellent example, thank you.

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mrajiullah commented Feb 16, 2016

How to take information such as download size, transfer time from multi interface?

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wjx0912 commented Feb 26, 2017

Excellent example, test success!

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albertino80 commented Mar 7, 2017

This example works, but if you set the CURLMOPT_MAX_HOST_CONNECTIONS this code will never exit from first loop ( while(still_running) ).
The fix is to call curl_multi_info_read also inside first loop.

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bhardwaj75 commented Sep 28, 2017

Hey, how to set timeout time for every individual request. Do you have any idea?

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