C++ 基于libcurl库，进行文件下载

通过libcurl下载文件，方法实现如下：

#include 
#include 
#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：

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