vc擷取時間函數總結

如何擷取時間？精度如何？                                                                    A: 1 使用time_t time( time_t * timer )       精確到秒 　　計算時間差使用double difftime( time_t timer1, time_t timer0 ) 2 使用clock_t clock() 得到的是CPU時間       精確到1/CLOCKS_PER_SEC秒 3 使用DWORD GetTickCount() 得到的是系統啟動並執行時間 精確到毫秒 4 如果使用MFC的CTime類，可以用CTime::GetCurrentTime() 精確到秒 5 要擷取高精度時間，可以使用        BOOL QueryPerformanceFrequency(LARGE_INTEGER *lpFrequency)擷取系統的計數器的頻率        BOOL QueryPerformanceCounter(LARGE_INTEGER *lpPerformanceCount)擷取計數器的值        然後用兩次計數器的差除以Frequency就得到時間。 6 還有David的文章中提到的方法：        Multimedia Timer Functions        The following functions are used with multimedia timers.        timeBeginPeriod/timeEndPeriod/timeGetDevCaps/timeGetSystemTime        timeGetTime/timeKillEvent/TimeProc/timeSetEvent     精度很高 Q:GetTickCount()函數，說是毫秒記數，是真的嗎，還是精確到55毫秒？ A: GetTickCount()和GetCurrentTime()都只精確到55ms(1個tick就是55ms)。如果要精確到毫秒，應該使用timeGetTime函數或QueryPerformanceCounter函數。具體例子可以參考QA001022 "VC++中使用高精度定時器"、QA001813 "如何在Windows實現準確的定時"和QA004842 "timeGetTime函數延時不準"。 Q:vc++怎樣擷取系統時間，傳回值是什麼類型的變數呢？ GetSystemTime返回的是格林威志標準時間 GetLocalTime，和上面用法一樣，返回的是你所在地區的時間，中國返回的是北京時間 VOID GetSystemTime( LPSYSTEMTIME lpSystemTime // address of system time structure ); 函數就可以獲得了，其中LPSYSTEMTIME 是個結構體 含：年，月，日，周幾，小時，分，秒，毫秒。 以下是Time的MSDN文檔: Compatibility in the Introduction. Libraries   LIBC.LIB Single thread static library, retail version LIBCMT.LIB Multithread static library, retail version MSVCRT.LIB Import library for MSVCRT.DLL, retail version   Return Value time returns the time in elapsed seconds. There is no error return. Parameter timer Storage location for time Remarks The time function returns the number of seconds elapsed since midnight (00:00:00), January 1, 1970, coordinated universal time, according to the system clock. The return value is stored in the location given by timer. This parameter may be NULL, in which case the return value is not stored.   Example /* TIMES.C illustrates various time and date functions including:  *        time              _ftime            ctime         asctime  *        localtime         gmtime            mktime        _tzset  *        _strtime          _strdate          strftime  *  * Also the global variable:  *        _tzname  */ #include <time.h> #include <stdio.h> #include <sys/types.h> #include <sys/timeb.h> #include <string.h> void main() {       char tmpbuf[128], ampm[] = "AM";       time_t ltime;       struct _timeb tstruct;       struct tm *today, *gmt, xmas = { 0, 0, 12, 25, 11, 93 };       /* Set time zone from TZ environment variable. If TZ is not set,        * the operating system is queried to obtain the default value        * for the variable.        */       _tzset();       /* Display operating system-style date and time. */       _strtime( tmpbuf );       printf( "OS time:/t/t/t/t%s/n", tmpbuf );       _strdate( tmpbuf );       printf( "OS date:/t/t/t/t%s/n", tmpbuf );       /* Get UNIX-style time and display as number and string. */       time( &ltime );       printf( "Time in seconds since UTC 1/1/70:/t%ld/n", ltime );       printf( "UNIX time and date:/t/t/t%s", ctime( &ltime ) );       /* Display UTC. */       gmt = gmtime( &ltime );       printf( "Coordinated universal time:/t/t%s", asctime( gmt ) );       /* Convert to time structure and adjust for PM if necessary. */       today = localtime( &ltime );       if( today->tm_hour > 12 )       {      strcpy( ampm, "PM" );      today->tm_hour -= 12;       }       if( today->tm_hour == 0 )    /* Adjust if midnight hour. */      today->tm_hour = 12;       /* Note how pointer addition is used to skip the first 11        * characters and printf is used to trim off terminating        * characters.        */       printf( "12-hour time:/t/t/t/t%.8s %s/n",          asctime( today ) + 11, ampm );       /* Print additional time information. */       _ftime( &tstruct );       printf( "Plus milliseconds:/t/t/t%u/n", tstruct.millitm );       printf( "Zone difference in seconds from UTC:/t%u/n",                tstruct.timezone );       printf( "Time zone name:/t/t/t/t%s/n", _tzname[0] );       printf( "Daylight savings:/t/t/t%s/n",                tstruct.dstflag ? "YES" : "NO" );       /* Make time for noon on Christmas, 1993. */       if( mktime( &xmas ) != (time_t)-1 )      printf( "Christmas/t/t/t/t%s/n", asctime( &xmas ) );       /* Use time structure to build a customized time string. */       today = localtime( &ltime );       /* Use strftime to build a customized time string. */       strftime( tmpbuf, 128,            "Today is %A, day %d of %B in the year %Y./n", today );       printf( tmpbuf ); }   Output OS time:                                  21:51:03 OS date:                                  05/03/94 Time in seconds since UTC 1/1/70:         768027063 UNIX time and date:                       Tue May 03 21:51:03 1994 Coordinated universal time:               Wed May 04 04:51:03 1994 12-hour time:                             09:51:03 PM Plus milliseconds:                        279 Zone difference in seconds from UTC:      480 Time zone name:                           Daylight savings:                         YES Christmas                                 Sat Dec 25 12:00:00 1993 Today is Tuesday, day 03 of May in the year 1994.