C++基于libcurl 的文件下载

首先基于环境的配置这里不做详细描述，请务必保证依赖所需的库文件加载进去

通过libcurl下载文件，方法实现如下：

#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:   要下载文件的url地址
		    outfilename:   下载文件指定的文件名
*/
int DOWNLOAD_FILE(const char* url, const char outfilename[FILENAME_MAX]){
	CURL *curl;
	FILE *fp;
	CURLcode res;
	/*   调用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;
	}
	/*  调用curl_easy_init()函数得到 easy interface型指针  */
	curl = curl_easy_init();
	if (curl) {

		fopen_s(&fp,outfilename,"wb"); 

		/*  调用curl_easy_setopt()设置传输选项 */
		res = curl_easy_setopt(curl, CURLOPT_URL, url);
		if (res != CURLE_OK)
		{
			fclose(fp);
			curl_easy_cleanup(curl);
			return -1;
		}
	    /*  根据curl_easy_setopt()设置的传输选项，实现回调函数以完成用户特定任务  */
		res = curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
		if (res != CURLE_OK)
		{
			fclose(fp);
			curl_easy_cleanup(curl);
			return -1;
		}
		/*  根据curl_easy_setopt()设置的传输选项，实现回调函数以完成用户特定任务  */
		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);                               // 调用curl_easy_perform()函数完成传输任务
		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);                                     // 调用curl_easy_cleanup()释放内存 

	}
	curl_global_cleanup();
	return 0;
}

以上代码是基于官方修改而成

官方的例子程序如下：

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2012, 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.
 *
 ***************************************************************************/
#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;
}