How to obtain system time in C Language

How to obtain system time in C Language

C LanguageHow to get the time? How accurate?
1 use time_t time (time_t * timer) to be accurate to seconds
2 using clock_t clock (), the CPU time is accurate to 1/CLOCKS_PER_SEC.
3. Calculate the time difference using double difftime (time_t timer1, time_t timer0)
4 Use DWORD GetTickCount () precise to milliseconds
5. If you use the CTime class of MFC, you can use CTime: GetCurrentTime () to precise to seconds.
6. You can use
BOOL QueryPerformanceFrequency (LARGE_INTEGER * lpFrequency)
Obtain the counter frequency of the system.
BOOL QueryPerformanceCounter (LARGE_INTEGER * lpPerformanceCount)
Obtains the counter value.
Then, divide the difference between two counters by Frequency to get the time.
7. Multimedia Timer Functions
The following functions are used with multimedia timers.
TimeBeginPeriod/timeEndPeriod/timeGetDevCaps/timeGetSystemTime
//************************************** *******************************
// Use standard C to obtain the current system time

I. time () function

The time (& rawtime) function returns the number of seconds from January 1, January 1, 1970, in seconds, and is stored in rawtime.
# Include "time. h"
Void main ()
{
Time_t rawtime;
Struct tm * timeinfo;
Time (& rawtime );
Timeinfo = localtime (& rawtime );
Printf ("/007The current date/time is: % s", asctime (timeinfo ));
Exit (0 );
}
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# Include -- the required time function header file
Time_t -- time type (time. h is defined as typedef long time_t; tracing, time_t is long)
Struct tm -- time structure, which is defined as follows:
Int tm_sec;
Int tm_min;
Int tm_hour;
Int tm_mday;
Int tm_mon;
Int tm_year;
Int tm_wday;
Int tm_yday;
Int tm_isdst;
Time (& rawtime); -- get time, in seconds, from January 1, January 1, 1970, stored in rawtime
Localtime (& rawtime); -- convert to local time, tm Time Structure
Asctime () -- convert to standard ASCII time format:
Week Month day hour: minute: second year

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Ii. clock () function. Use the clock () function to obtain the millisecond-level time after the system is started. divide it by CLOCKS_PER_SEC and replace it with the standard c function.
Clock_t clock (void );
# Include
Clock_t t = clock ();
Long sec = t/CLOCKS_PER_SEC;
It records the clock cycle, and the implementation does not seem very accurate and requires experimental verification;
---------------------------------------------------------------------------
3. gettime (& t); it is said that the time structure of tc2.0 contains millisecond Information
# Include
# Include
Int main (void)
{
Struct time t;
Gettime (& t );
Printf ("The current time is: % 2d: % 02d: % 02d. % 02d/n ",
T. ti_hour, t. ti_min, t. ti_sec, t. ti_hund );
Return 0;
}
Time is a struct, in which the member function ti_hund is millisecond...

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4. GetTickCount (), which is a function commonly used in windows to calculate the running time;
DWORD dwStart = GetTickCount ();
// Run your program code here
DWORD dwEnd = GetTickCount ();
Then (dwEnd-dwStart) Is your program running time, in milliseconds
This function is only accurate to 55 ms, and one tick is 55 ms.
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5. timeGetTime () t, imeGetTime () is basically equal to GetTickCount (), but the accuracy is higher
DWORD dwStart = timeGetTime ();
// Run your program code here
DWORD dwEnd = timeGetTime ();
Then (dwEnd-dwStart) Is your program running time, in milliseconds
Although the unit of returned values should be ms, the legend shows that the precision is only 10 ms.
========================================================== =
//************************************** * *************************** Unix
# Unix time-related, also standard library
//************************************** *******************************
1. The timegm function only converts the struct tm structure to the time_t structure without the time zone information;
Time_t timegm (struct tm * tm );
2. mktime uses time zone information
Time_t mktime (struct tm * tm );
The timelocal function is a GNU extension equivalent to the posix function mktime.
Time_t timelocal (struct tm * tm );
3. The gmtime function only converts the time_t structure to the struct tm structure without the time zone information;
Struct tm * gmtime (const time_t * clock );
4. Use the time zone information for localtime
Struct tm * localtime (const time_t * clock );
1. Obtain the time and set the time in stime.
Time_t t;
T = time (& t );
2. The stime parameter should be the GMT time, which is set to the local time according to the local time zone;
Int stime (time_t * tp)
3. UTC = true indicates that the Daylight Saving Time is used;
4. The modification time and other information of the file are all stored in GMT. Different systems use localtime to convert the local time after obtaining the modification time;
5. We recommend that you use setup to set the time zone;
6. You can change the time zone to the setting in/etc/sysconfig/clock and then re-apply ln-fs/usr/share/zoneinfo/xxxx/xxx/etc/localtime.
Time_t can only represent the range of 68 years, that is, mktime can only return time_t in the range of 1970-2038
Check whether your system has time_t64, which can indicate a larger time range.
//************************************** * ************************* Windows
# Some differences in Window
//************************************** *******************************

I. CTime () Class
VC Programming generally uses the CTime class to obtain the current date and time

CTime t = GetCurrentTime ();
The SYSTEMTIME structure contains millisecond information.
Typedef struct _ SYSTEMTIME {
WORD wYear;
WORD wMonth;
WORD wDayOfWeek;
WORD wDay;
WORD wHour;
WORD wMinute;
WORD wSecond;
WORD wMilliseconds;
} SYSTEMTIME, * PSYSTEMTIME;
SYSTEMTIME t1;
GetSystemTime (& t1)
CTime curTime (t1 );
Word ms = t1.wMilliseconds;
SYSTEMTIME interval m;
: GetLocalTime (& M );
_ Strtime () in time. h // can only be used in windows
Char t [11];
_ Strtime (t );
Puts (t );

//*****************************
Obtain the current date and time
CTime tm = CTime: GetCurrentTime ();
CString str = tm. Format ("% Y-% m-% d ");
In VC, we can use the CTime class to obtain the current date of the system. The usage is as follows:
CTime t = CTime: GetCurrentTime (); // obtain the system date, stored in t
Int d = t. GetDay (); // obtain the current date
Int y = t. GetYear (); // get the current year
Int m = t. GetMonth (); // get the current month
Int h = t. GetHour (); // obtain the current time
Int mm = t. GetMinute (); // get the current minute
Int s = t. GetSecond (); // get the current second
Int w = t. GetDayOfWeek (); // obtain the day of the week. Note that 1 is Sunday and 7 is Saturday.

Ii. CTimeSpan class
To calculate the difference between the two periods, you can use the CTimeSpan class. The usage is as follows:
CTime t1 (1999, 3, 19, 22, 15, 0 );
CTime t = CTime: GetCurrentTime ();
CTimeSpan span = t-t1; // calculate the interval between the current system time and time t1
Int iDay = span. GetDays (); // obtain the total number of days of the interval.
Int iHour = span. GetTotalHours (); // obtain the total number of hours
Int iMin = span. GetTotalMinutes (); // obtain the total number of minutes
Int iSec = span. GetTotalSeconds (); // gets the total number of seconds

------------------------------------------------------------------------------

3. _ timeb () function
_ Timeb is defined in SYS/TIMEB. H and has four fields.
Dstflag
Millitm
Time
Timezone
Void _ ftime (struct _ timeb * timeptr );
Struct _ timeb timebuffer;
_ Ftime (& timebuffer );
Take the current time: the document can be described in ms. Someone tests it, as if it could only be 16 ms!

4. Set a timer
Define TIMER ID
# Define TIMERID_JISUANFANGSHI 2
Set the clock in a proper place, where you need to start its function;
SetTimer (TIMERID_JISUANFANGSHI, 200, NULL );
Destroy the clock when no timer is required
KillTimer (TIMERID_JISUANFANGSHI );
Message ing corresponding to VC program
Void CJisuan: OnTimer (UINT nIDEvent)
{Switch (nIDEvent )}
Bytes ---------------------------------------------------------------------------------------
# How to set the current system time ------------------------------------- windows
SYSTEMTIME m_myLocalTime, * lpSystemTime;
M_myLocalTime.wYear = 2003;
M_myLocalTime.wM;
M_myLocalTime.wDay = 1;
M_myLocalTime.wHour = 0;
M_myLocalTime.wMinute = 0;
M_myLocalTime.wSec;
M_myLocalTime.wMillisec;
LpSystemTime = & m_myLocalTime;
If (SetLocalTime (lpSystemTime) // you cannot change it to SetSystemTime ().
MessageBox ("OK! ");
Else
MessageBox ("Error! ");
SYSTEMTIME m_myLocalTime, * lpSystemTime;
M_myLocalTime.wYear = 2003;
M_myLocalTime.wM;
M_myLocalTime.wDay = 1;
LpSystemTime = & m_myLocalTime;
If (SetDate (lpSystemTime) // it cannot be changed to SetSystemTime ().
MessageBox ("OK! ");
Else
MessageBox ("Error! ");