首先，调用函数curl_global_init()来初始化库函数；记得最后调用curl_global_cleanup()来释放库资源。其次，调用curl_easy_init()来初始化一个句柄，得到一个easy interface型指针；curl_easy_init函数是线程相关的，也就是说不能在一个线程中调用另外一个线程通过curl_easy_init创建的CURL指针。

记得最后要调用curl_easy_cleanup(easy interface);接着，再调用curl_easy_setopt来设置将要访问的网络地址。curl_easy_perform来执行下载。

注意的是：libcurl的全局初始化必须放在线程之外。

1、函数

CURLcode curl_easy_setopt(CURL *handle， CURLoption option， parameter);

CURLOPT_WRITEFUNCTION //设置回调函数

回调函数原型为: size_t function( void *ptr， size_t size， size_t nmemb， void *userp);函数将在libcurl接收到数据后被调用。

void *ptr是下载回来的数据.

void *userp是用户指针，用户通过这个指针传输自己的数据。

CURLOPT_WRITEDATA

设置回调函数中的void *userp指针的来源。

CURLOPT_URL

设置访问的URI。

CURLOPT_TIMEOUT

超时时间。

CURLOPT_CONNECTIONTIMEOUT

连接等待时间。

CURLOPT_RANGE

断点续传，指定传输分片，格式:"0-200"

示例代码1

/*************************************************************************** *                                  _   _ ____  _ *  Project                     ___| | | |  _ \| | *                             / __| | | | |_) | | *                            | (__| |_| |  _ <| |___ *                             \___|\___/|_| \_\_____| * * Copyright (C) 1998 - 2011, Daniel Stenberg, 
       
        , et al. * * This software is licensed as described in the file COPYING, which * you should have received as part of this distribution. The terms * are also available at http://curl.haxx.se/docs/copyright.html. * * You may opt to use, copy, modify, merge, publish, distribute and/or sell * copies of the Software, and permit persons to whom the Software is * furnished to do so, under the terms of the COPYING file. * * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY * KIND, either express or implied. * ***************************************************************************/ /* A multi-threaded example that uses pthreads extensively to fetch * X remote files at once */  #include 
        
         #include 
         
          #include 
          
            #define NUMT 4 /*  List of URLs to fetch.   If you intend to use a SSL-based protocol here you MUST setup the OpenSSL  callback functions as described here:   http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION */ const char * const urls[NUMT]= {  "http://curl.haxx.se/",  "ftp://cool.haxx.se/",  "http://www.contactor.se/",  "www.haxx.se"}; static void *pull_one_url(void *url){  CURL *curl;   curl = curl_easy_init();  curl_easy_setopt(curl, CURLOPT_URL, url);  curl_easy_perform(curl); /* ignores error */   curl_easy_cleanup(curl);   return NULL;}  /*   int pthread_create(pthread_t *new_thread_ID,   const pthread_attr_t *attr,   void * (*start_func)(void *), void *arg);*/  int main(int argc, char **argv){  pthread_t tid[NUMT];  int i;  int error;   /* Must initialize libcurl before any threads are started */   curl_global_init(CURL_GLOBAL_ALL);   for(i=0; i< NUMT; i++) {    error = pthread_create(&tid[i],                           NULL, /* default attributes please */                            pull_one_url,                           (void *)urls[i]);    if(0 != error)      fprintf(stderr, "Couldn't run thread number %d, errno %d\n", i, error);    else      fprintf(stderr, "Thread %d, gets %s\n", i, urls[i]);  }   /* now wait for all threads to terminate */   for(i=0; i< NUMT; i++) {    error = pthread_join(tid[i], NULL);    fprintf(stderr, "Thread %d terminated\n", i);  }   return 0;}
          
         
        
       

示例代码2

获取网站包括HTTP头部信息在内的500字节数据size_t callback_get_head(void *ptr, size_t size, size_t nmemb, void *userp) {    strcat( userp, ptr);    return size * nmemb;     //必须返回这个大小, 否则只回调一次 } void *get_head_thread(void *) {    CURL *curl = curl_easy_init();        curl_easy_setopt(curl, CURLOPT_URL, "www.163.com"); //设置下载的URI    curl_easy_setopt(curl, CURLOPT_TIMEOUT, 20);        //设置超时    curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);        //屏蔽其它信号    curl_easy_setopt(curl, CURLOPT_HEADER, 1);          //下载数据包括HTTP头部    curl_easy_setopt(curl, CURLOPT_RANGE, "0-500");     //用于断点续传, 设置下载的分片        char buffer[MAXHEADLEN] = {
     0x0};    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, callback_get_head); //设置下载数据的回调函数    curl_easy_setopt(curl, CURLOPT_WRITEDATA, buffer);      curl_easy_perform(curl);      curl_easy_cleanup(curl);    //此时网站HTTP头信息已经存放在buffer内. }

 

参考

[1]http://curl.haxx.se/libcurl/c/multithread.html

[2]http://blog.csdn.net/aaa20090987/article/details/7955918

[3]http://hi.baidu.com/445920201/item/99401f1674bf4b5e2a3e22b4

[4]http://blog.chinaunix.net/uid-20692625-id-3203258.html