windows io 异步读写

最新推荐文章于 2021-02-10 21:27:25 发布

原创最新推荐文章于 2021-02-10 21:27:25 发布 · 1.7k 阅读

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#windows #io #null #object #include #file

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本文介绍了一个使用Windows API进行异步I/O操作的例子，包括文件的读写操作及通过事件来监控这些操作的状态。文章详细展示了如何使用CreateFile、ReadFile、WriteFile等函数，并解释了事件的信号状态管理。

#include <windows.h> #include <stdio.h> void main() { HANDLE hfile = CreateFile("test.txt",GENERIC_READ | GENERIC_WRITE, 0,NULL,CREATE_ALWAYS, FILE_FLAG_OVERLAPPED | FILE_ATTRIBUTE_NORMAL,NULL); if (hfile == INVALID_HANDLE_VALUE) { printf("invalid handle value./n"); } OVERLAPPED oWrite = { 0 }; oWrite.Offset = 0; oWrite.hEvent = CreateEvent(NULL,FALSE,FALSE,NULL); WriteFile(hfile, "Jeffery chen", 14, NULL, &oWrite); BYTE bBuffer[10]; OVERLAPPED oRead = { 0 }; oRead.Offset = 5; /**start from 6 char */ oRead.hEvent = CreateEvent(NULL,FALSE,FALSE,NULL); ReadFile(hfile, bBuffer, 10, NULL, &oRead); HANDLE h[2]; h[0] = oRead.hEvent; h[1] = oWrite.hEvent; while (true) { Sleep(3000); DWORD dw = WaitForMultipleObjects(2, h, FALSE, 1000); if(dw == WAIT_OBJECT_0) { printf("can be read./n"); oRead.Offset += 1; // ReadFile(hfile,bBuffer,10,NULL,&oRead); // Handle to an event set to the signaled state when the transfer has been completed //当调用完ReadFile后，会自动设置到有信号状态。 printf("%s/n",bBuffer); } else if (dw == (WAIT_OBJECT_0 + 1)) { printf("can write io./n"); // WriteFile(hfile,"shawn",6,NULL,&oWrite); // Handle to an event set to the signaled state when the transfer has been completed } else break; } getchar(); }

在创建event时，第二个参数表明是否为manual-reset event，此处设为false，表明系统自动管理。

当调用WaitForMultipleObject时使信号处于无信号状态。

当调用ReadFile或WriteFile时使信号处于有信号状态。