windows文件异步写示例

windows中文件读写是否异步，主要看在CreateFile的时候，有无传递FILE_FLAG_OVERLAPPED标记位，代码如下。
同时本人曾经写过用IO完成端口实现文件读操作的文章，地址如下：
IO完成端口实现文件异步读操作

// FileOverlappedWrite.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <Windows.h>

HANDLE hFileRead = INVALID_HANDLE_VALUE;
HANDLE hFileWrite = INVALID_HANDLE_VALUE;

#define LEN_READ_WRITE 1024

int main()
{
    
    
	hFileRead = CreateFile("D:\\video\\xingjichuanyue.rmvb", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
	if (hFileRead == INVALID_HANDLE_VALUE)
	{
    
    
		return -1;
	}

	hFileWrite = CreateFile("D:\\video\\xingjichuanyue_normal.rmvb", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_FLAG_OVERLAPPED, NULL);
	if (hFileWrite == INVALID_HANDLE_VALUE)
	{
    
    
		return -1;
	}

	OVERLAPPED *overlap = new OVERLAPPED;
	overlap->Offset = 0;
	overlap->OffsetHigh = 0;
	overlap->hEvent = NULL;

	LARGE_INTEGER liCurrentPosition = {
    
     0 };
	while (1)
	{
    
    
		char szBuffer[LEN_READ_WRITE + 2] = {
    
     0 };
		DWORD dwReaded = 0;
		if (ReadFile(hFileRead, szBuffer, LEN_READ_WRITE, &dwReaded, NULL))
		{
    
    
			if (dwReaded > 0)
			{
    
    
				WriteFile(hFileWrite, szBuffer, dwReaded, NULL, overlap);
				overlap->Offset += dwReaded;
			}
			else
			{
    
    
				break;
			}
		}
		else
		{
    
    
			break;
		}
	}
	CloseHandle(hFileWrite);
	CloseHandle(hFileRead);
    return 0;
}