C++基於libcurl 的文件下載

首先基於環境的配置這里不做詳細描述，請務必保證依賴所需的庫文件加載進去

通過libcurl下載文件，方法實現如下：

#include <stdio.h>
#include <curl/curl.h>
#include "DownloadInfo.h"

/************************************************************************/
/*    create by: mengxiaoxin   date:2014/12/9                           */
/************************************************************************/


/*  libcurl write callback function */
size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
	size_t written = fwrite(ptr, size, nmemb, stream);
	return written;
}


/*			
			   Function:   libcurl connection initialization  download  file
			 Parameters:   (const char* url, const char outfilename[FILENAME_MAX])
			        url:   要下載文件的url地址
		    outfilename:   下載文件指定的文件名
*/
int DOWNLOAD_FILE(const char* url, const char outfilename[FILENAME_MAX]){
	CURL *curl;
	FILE *fp;
	CURLcode res;
	/*   調用curl_global_init()初始化libcurl  */
	res = curl_global_init(CURL_GLOBAL_ALL);
	if (CURLE_OK != res)
	{
		printf("init libcurl failed.");
		curl_global_cleanup();
		return -1;
	}
	/*  調用curl_easy_init()函數得到 easy interface型指針  */
	curl = curl_easy_init();	
	if (curl) {

		fopen_s(&fp,outfilename,"wb"); 
		
		/*  調用curl_easy_setopt()設置傳輸選項 */
		res = curl_easy_setopt(curl, CURLOPT_URL, url);                  
		if (res != CURLE_OK)
		{	
			fclose(fp);
			curl_easy_cleanup(curl);  
			return -1;
		}
	    /*  根據curl_easy_setopt()設置的傳輸選項，實現回調函數以完成用戶特定任務  */
		res = curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);  
		if (res != CURLE_OK)
		{	
			fclose(fp);
			curl_easy_cleanup(curl);  
			return -1;
		}
		/*  根據curl_easy_setopt()設置的傳輸選項，實現回調函數以完成用戶特定任務  */
		res = curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
		if (res != CURLE_OK)
		{	
			fclose(fp);	
			curl_easy_cleanup(curl);  
			return -1;
		}

		res = curl_easy_perform(curl);                               // 調用curl_easy_perform()函數完成傳輸任務
		fclose(fp);	
		/* Check for errors */ 
		if(res != CURLE_OK){
			fprintf(stderr, "curl_easy_perform() failed: %s\n",curl_easy_strerror(res));
			curl_easy_cleanup(curl);  
			return -1;
		}
			
		/* always cleanup */
		curl_easy_cleanup(curl);                                     // 調用curl_easy_cleanup()釋放內存 
		
	}
	curl_global_cleanup();
	return 0;
}

以上代碼是基於官方修改而成

官方的例子程序如下：

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2012, Daniel Stenberg, <[e-mail]>, 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.
 *
 ***************************************************************************/ 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
#include <curl/curl.h>
 
static size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream)
{
  size_t written = fwrite(ptr, size, nmemb, (FILE *)stream);
  return written;
}
 
int main(int argc, char *argv[])
{
  CURL *curl_handle;
  static const char *pagefilename = "page.out";
  FILE *pagefile;
 
  if(argc < 2 ) {
    printf("Usage: %s <URL>\n", argv[0]);
    return 1;
  }
 
  curl_global_init(CURL_GLOBAL_ALL);
 
  /* init the curl session */ 
  curl_handle = curl_easy_init();
 
  /* set URL to get here */ 
  curl_easy_setopt(curl_handle, CURLOPT_URL, argv[1]);
 
  /* Switch on full protocol/debug output while testing */ 
  curl_easy_setopt(curl_handle, CURLOPT_VERBOSE, 1L);
 
  /* disable progress meter, set to 0L to enable and disable debug output */ 
  curl_easy_setopt(curl_handle, CURLOPT_NOPROGRESS, 1L);
 
  /* send all data to this function  */ 
  curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, write_data);
 
  /* open the file */ 
  pagefile = fopen(pagefilename, "wb");
  if (pagefile) {
 
    /* write the page body to this file handle */ 
    curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, pagefile);
 
    /* get it! */ 
    curl_easy_perform(curl_handle);
 
    /* close the header file */ 
    fclose(pagefile);
  }
 
  /* cleanup curl stuff */ 
  curl_easy_cleanup(curl_handle);
 
  return 0;
}