使用wininet的InternetReadFile下载文件

简单地说，wininet是微软提供的用来制作网络客户端程序的类库，它封装了winsock，为开发人员提供易用的开发接口。

基本上每天我们都会从网络上上传或下载一些文件。今天就简单地使用wininet函数实现下载文件的功能。代码如下：

 #include <windows.h>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <wininet.h>
#include <shellApi.h>
#include <ShlObj.h>

#pragma comment(lib,"wininet")

using namespace std;

bool DownloadFile(LPCTSTR szUrl,LPCTSTR szLocalFile,BOOL bFailIfExists);

int main(int argc, char* argv[])
{
std::cout<<DownloadFile("http://hi.baidu.com/new/failnorth","d:\\failnorth.htm",TRUE)<<std::endl;
getchar();
return 0;
}

bool DownloadFile(LPCTSTR szUrl,LPCTSTR szLocalFile,BOOL bFailIfExists)
{
if (bFailIfExists &&
!PathIsDirectory(szLocalFile) &&
(GetFileAttributes(szLocalFile) != INVALID_FILE_ATTRIBUTES))
{
return false;
}
HANDLE hFile = INVALID_HANDLE_VALUE;
HINTERNET hInet = NULL;
HINTERNET hUrl = NULL;
DWORD dwBuf = 1024*1024,dwRead = 0; //1M
auto_ptr<char> szBuf(new char[dwBuf]);
memset(szBuf.get(),0,dwBuf);
std::string strTmp;
bool bRet = false;
try
{
hFile = CreateFile(szLocalFile,GENERIC_READ|GENERIC_WRITE,0,NULL,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL);
if (hFile == INVALID_HANDLE_VALUE)
throw "error";
hInet = InternetOpen(NULL,INTERNET_OPEN_TYPE_PRECONFIG,NULL,NULL,0);
if (hInet == NULL)
throw "error";
hUrl = InternetOpenUrl(hInet,szUrl,NULL,0,
INTERNET_FLAG_TRANSFER_BINARY|INTERNET_FLAG_NO_CACHE_WRITE|INTERNET_FLAG_RELOAD,0);
if (hUrl == NULL)
throw "error";
for(;;)
{
if (!InternetReadFile(hUrl,szBuf.get(),dwBuf,&dwRead))
{
bRet = false;
break;
}
if (dwRead == 0)
{
bRet = true;
break;
}
//strTmp += std::string(szBuf,dwRead);
WriteFile(hFile,szBuf.get(),dwRead,&dwRead,NULL);
}
throw "ok";
}
catch(...)
{
if (hFile != INVALID_HANDLE_VALUE)
CloseHandle(hFile);
if (hUrl != NULL)
InternetCloseHandle(hUrl);
if (hInet != NULL)
InternetCloseHandle(hInet);
}

return bRet;
}