Windows下的多媒體定時器:timeSetEvent 使用方法及易出錯的幾種情況
MMRESULT timeSetEvent( UINT uDelay, UINT uResolution, LPTIMECALLBACK lpTimeProc, WORD dwUser, UINT fuEvent )
其中: uDelay:以毫秒指定事件的週期。
Uresolution:以毫秒指定延時的精度,數值越小定時器事件解析度越高。預設值為1ms。
LpTimeProc:指向一個回撥函式。
DwUser:存放使用者提供的回撥資料。
FuEvent:指定定時器事件型別:
TIME_ONESHOT:uDelay毫秒後只產生一次事件
TIME_PERIODIC :每隔uDelay毫秒週期性地產生事件。
參照函式的說明,函式很容易使用,但在使用的過程中應該注意以下幾點,嚴格按照MSDN的介紹:
1,回撥函式的使用
在使用回撥函式的時候,一定要注意回撥函式的使用方法,MSDN上的說法如下,Pointer to a callback function that is called once upon expiration of a single event or periodically upon expiration of periodic events. If fuEventspecifies the TIME_CALLBACK_EVENT_SET or TIME_CALLBACK_EVENT_PULSE flag, then the lpTimeProc parameter is interpreted as a handle to an event object. The event will be set or pulsed upon completion of a single event or periodically upon completion of periodic events. For any other value of fuEvent, the lpTimeProc parameter is interpreted as a function pointer with the following signature: void (CALLBACK)(UINT uTimerID, UINT uMsg, DWORD_PTR dwUser, DWORD_PTR dw1, DWORD_PTR dw2);注意紅色部分在函式中一定不能丟掉,否則會引起程式的崩潰出現: 0x00000000 處有未經處理的異常: 0xC0000005: Access violation
2,timeKillEvent 關掉定時器的函式,一定要一一對應,每次timeSetEvent返回的定時器的ID是不一樣的,也就是說呼叫一次timeSetEvent就會產生一次Id,就是說,呼叫幾次timeSetEvent,就需要呼叫幾次timeKillEvent ,而且必須是相對應的ID,否則可能出現程式崩潰!!!!!
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具體的程式程式碼除錯如下:
// timeset.cpp : 定義控制檯應用程式的入口點。
//
#include "stdafx.h"
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#pragma comment(lib,"Winmm.lib")
#define delaytime 1000
int gtime_ID;
void CALLBACK TimeEvent(UINT uTimerID, UINT uMsg, DWORD_PTR dwUser, DWORD_PTR dw1, DWORD_PTR dw2)
{
printf("time ID is %d, started,dwUser is %d\n",gtime_ID, dwUser);
return;
}
void StartEventTime(DWORD_PTR duser)
{
gtime_ID = timeSetEvent(delaytime,10,(LPTIMECALLBACK)TimeEvent,duser,TIME_PERIODIC);
if(gtime_ID == NULL)
{
printf("time ID is not created\n");
return;
}
return;
}
int _tmain(int argc, _TCHAR* argv[])
{
int i = 0;
while (1)
{
StartEventTime(i);
Sleep(1100);
i++;
timeKillEvent(gtime_ID);
if (i == 10)
{
break;
}
}
return 0;
}
int gtime_ID7,gtime_ID40,tmpcnt1=0,tmpcnt2=0;
#define delaytime 1
void CALLBACK TimeEvent7(UINT uTimerID, UINT uMsg, DWORD_PTR dwUser, DWORD_PTR dw1, DWORD_PTR dw2)
{
printf("%d time1:%d\n",tmpcnt1++,timeGetTime());
return;
}
void CALLBACK TimeEvent40(UINT uTimerID, UINT uMsg, DWORD_PTR dwUser, DWORD_PTR dw1, DWORD_PTR dw2)
{
printf(" %d time2:%d\n",tmpcnt2++,timeGetTime());
return;
}
int main()
{
gtime_ID7 = timeSetEvent(7,1,(LPTIMECALLBACK)TimeEvent7,0,TIME_PERIODIC);
gtime_ID40 = timeSetEvent(40,1,(LPTIMECALLBACK)TimeEvent40,0,TIME_PERIODIC);
Sleep(1000);
timeKillEvent(gtime_ID7);
timeKillEvent(gtime_ID40);
getchar();
return 0;
}