curl简单使用

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

View Code

/***************************************************************************

 *                                  _   _ ____  _

 *  Project                     ___| | | |  _ \| |

 *                             / __| | | | |_) | |

 *                            | (__| |_| |  _ <| |___

 *                             \___|\___/|_| \_\_____|

 *

 * Copyright (C) 1998 - 2011, Daniel Stenberg, <[email protected]>, 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 <stdio.h>

#include <pthread.h>

#include <curl/curl.h>

 

#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

View Code

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