监视通信事件
以下示例代码打开重叠 I/O 的串行端口,创建一个事件掩码来监视 CTS 和 DSR 信号,然后等待事件发生。 WaitCommEvent 函数应作为重叠操作执行,以便进程的其他线程可以在等待期间执行 I/O 操作。
#include <windows.h>
#include <tchar.h>
#include <assert.h>
#include <stdio.h>
void _tmain(
int argc,
TCHAR *argv[]
)
{
HANDLE hCom;
OVERLAPPED o;
BOOL fSuccess;
DWORD dwEvtMask;
hCom = CreateFile( TEXT("\\\\.\\COM1"),
GENERIC_READ | GENERIC_WRITE,
0, // exclusive access
NULL, // default security attributes
OPEN_EXISTING,
FILE_FLAG_OVERLAPPED,
NULL
);
if (hCom == INVALID_HANDLE_VALUE)
{
// Handle the error.
printf("CreateFile failed with error %d.\n", GetLastError());
return;
}
// Set the event mask.
fSuccess = SetCommMask(hCom, EV_CTS | EV_DSR);
if (!fSuccess)
{
// Handle the error.
printf("SetCommMask failed with error %d.\n", GetLastError());
return;
}
// Create an event object for use by WaitCommEvent.
o.hEvent = CreateEvent(
NULL, // default security attributes
TRUE, // manual-reset event
FALSE, // not signaled
NULL // no name
);
// Initialize the rest of the OVERLAPPED structure to zero.
o.Internal = 0;
o.InternalHigh = 0;
o.Offset = 0;
o.OffsetHigh = 0;
assert(o.hEvent);
if (WaitCommEvent(hCom, &dwEvtMask, &o))
{
if (dwEvtMask & EV_DSR)
{
// To do.
}
if (dwEvtMask & EV_CTS)
{
// To do.
}
}
else
{
DWORD dwRet = GetLastError();
if( ERROR_IO_PENDING == dwRet)
{
printf("I/O is pending...\n");
// To do.
}
else
printf("Wait failed with error %d.\n", GetLastError());
}
}