异步读写之利用完成历程

// Overlapped.cpp : 定义控制台应用程序的入口点。

#include "stdafx.h"
#include <windows.h>
#include <iostream>
using namespace std;
VOID CALLBACK CompletionRoutine(
_In_ DWORD ErrorCode,
_In_ DWORD ReturnLength,
_Inout_ LPOVERLAPPED Overlapped);
HANDLE __FileHandle = NULL;
char __BufferData[20] = {0};

int main()
{
BOOL IsOk = FALSE;
OVERLAPPED Overlapped = { 0 };
__FileHandle = CreateFile(L"ReadMe.txt", GENERIC_ALL, FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL|FILE_FLAG_OVERLAPPED, NULL);
if (__FileHandle == INVALID_HANDLE_VALUE)
{
int LastError = GetLastError();
goto Exit;
}
//通知IO有异步IO和Overlapped的设置，读四个字节每次
//不用等待是因为没有创建事件当然不用搞
//OverLapped这里的作用是利用Overlapped->Offset 往下加字节设置位置读取字节
IsOk = ReadFileEx(__FileHandle, __BufferData, 4,&Overlapped,
(LPOVERLAPPED_COMPLETION_ROUTINE)CompletionRoutine);
if (IsOk == FALSE)
{
int LastError = GetLastError();
if (LastError == ERROR_IO_PENDING)
{
}
}
Exit:
SleepEx(0,TRUE);//只有为TRUE时候，等待完成历程返回时退出
if (__FileHandle != NULL)
{
CloseHandle(__FileHandle);
__FileHandle = NULL;
}
printf("Input AnyKey To Exit ");
getchar();
return 0;
}
VOID CALLBACK CompletionRoutine(
_In_ DWORD ErrorCode,
_In_ DWORD ReturnLength,
_Inout_ LPOVERLAPPED Overlapped
)
{
if (ErrorCode == ERROR_SUCCESS)
{
int i = 0;
for (i = 0; i < ReturnLength; i++)
{
printf("%c", __BufferData[i]);
}

Overlapped->Offset += ReturnLength;//
ReadFileEx(__FileHandle, __BufferData, 4, Overlapped,
(LPOVERLAPPED_COMPLETION_ROUTINE)CompletionRoutine);
}
else if (ErrorCode==ERROR_HANDLE_EOF)
{
//数据完成
printf(" ");
GetFileSize
}
else
{

}
}