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Tricks of the Windows Gam…ming Gurus (2nd Edition)
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Disc2.iso
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vc98
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crt
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src
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time.c
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C/C++ Source or Header
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1998-06-17
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5KB
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164 lines
/***
*time.c - get current system time
*
* Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* defines time() - gets the current system time and converts it to
* internal (time_t) format time.
*
*******************************************************************************/
#include <cruntime.h>
#include <time.h>
#include <internal.h>
#ifdef _WIN32
#include <windows.h>
#else /* _WIN32 */
#if defined (_M_MPPC) || defined (_M_M68K)
#include <macos\osutils.h> /* get DataTimeRec type */
#endif /* defined (_M_MPPC) || defined (_M_M68K) */
#endif /* _WIN32 */
#ifdef _WIN32
/*
* Cache holding the last time (GMT) for which the Daylight time status was
* determined by an API call.
*/
static SYSTEMTIME gmt_cache;
/*
* Three values of dstflag_cache and dstflag (local variable in code
* below)
*/
#define DAYLIGHT_TIME 1
#define STANDARD_TIME 0
#define UNKNOWN_TIME -1
static int dstflag_cache;
#endif /* _WIN32 */
/***
*time_t time(timeptr) - Get current system time and convert to time_t value.
*
*Purpose:
* Gets the current date and time and stores it in internal (time_t)
* format. The time is returned and stored via the pointer passed in
* timeptr. If timeptr == NULL, the time is only returned, not stored in
* *timeptr. The internal (time_t) format is the number of seconds since
* 00:00:00, Jan 1 1970 (UTC).
*
* Note: We cannot use GetSystemTime since its return is ambiguous. In
* Windows NT, in return UTC. In Win32S, probably also Win32C, it
* returns local time.
*
*Entry:
* time_t *timeptr - pointer to long to store time in.
*
*Exit:
* returns the current time.
*
*Exceptions:
*
*******************************************************************************/
time_t __cdecl time (
time_t *timeptr
)
{
time_t tim;
#ifdef _WIN32
SYSTEMTIME loct, gmt;
TIME_ZONE_INFORMATION tzinfo;
DWORD tzstate;
int dstflag;
/*
* Get local time from Win32
*/
GetLocalTime( &loct );
/*
* Determine whether or not the local time is a Daylight Saving
* Time. On Windows NT, the GetTimeZoneInformation API is *VERY*
* expensive. The scheme below is intended to avoid this API call in
* many important case by caching the GMT value and dstflag.In a
* subsequent call to time(), the cached value of dstflag is used
* unless the new GMT differs from the cached value at least in the
* minutes place.
*/
GetSystemTime( &gmt );
if ( (gmt.wMinute == gmt_cache.wMinute) &&
(gmt.wHour == gmt_cache.wHour) &&
(gmt.wDay == gmt_cache.wDay) &&
(gmt.wMonth == gmt_cache.wMonth) &&
(gmt.wYear == gmt_cache.wYear) )
{
dstflag = dstflag_cache;
}
else
{
if ( (tzstate = GetTimeZoneInformation( &tzinfo )) != 0xFFFFFFFF )
{
/*
* Must be very careful in determining whether or not DST is
* really in effect.
*/
if ( (tzstate == TIME_ZONE_ID_DAYLIGHT) &&
(tzinfo.DaylightDate.wMonth != 0) &&
(tzinfo.DaylightBias != 0) )
dstflag = DAYLIGHT_TIME;
else
/*
* When in doubt, assume standard time
*/
dstflag = STANDARD_TIME;
}
else
dstflag = UNKNOWN_TIME;
dstflag_cache = dstflag;
gmt_cache = gmt;
}
/* convert using our private routine */
tim = __loctotime_t( (int)loct.wYear,
(int)loct.wMonth,
(int)loct.wDay,
(int)loct.wHour,
(int)loct.wMinute,
(int)loct.wSecond,
dstflag );
#else /* _WIN32 */
#if defined (_M_MPPC) || defined (_M_M68K)
DateTimeRec dt;
GetTime(&dt);
/* convert using our private routine */
tim = _gmtotime_t((int)dt.year,
(int)dt.month,
(int)dt.day,
(int)dt.hour,
dt.minute,
dt.second);
#endif /* defined (_M_MPPC) || defined (_M_M68K) */
#endif /* _WIN32 */
if (timeptr)
*timeptr = tim; /* store time if requested */
return tim;
}