c语言计算时间的编程,C语言实现时间戳转日期的算法(推荐)
1、算法
時(shí)間是有周期規(guī)律的,4年一個(gè)周期(平年、平年、平年、閏年)共計(jì)1461天。Windows上C庫函數(shù)time(NULL)返回的是從1970年1月1日以來的毫秒數(shù),我們最后算出來的年數(shù)一定要加上這個(gè)基數(shù)1970。總的天數(shù)除以1461就可以知道經(jīng)歷了多少個(gè)周期;總的天數(shù)對1461取余數(shù)就可以知道剩余的不足一個(gè)周期的天數(shù),對這個(gè)余數(shù)進(jìn)行判斷也就可以得到月份和日了。
當(dāng)然了,C語言庫函數(shù):localtime就可以獲得一個(gè)時(shí)間戳對應(yīng)的具體日期了,這里 主要說的是實(shí)現(xiàn)的一種算法。
2、C語言代碼實(shí)現(xiàn)
int nTime = time(NULL);//得到當(dāng)前系統(tǒng)時(shí)間
int nDays = nTime/DAYMS + 1;//time函數(shù)獲取的是從1970年以來的毫秒數(shù),因此需要先得到天數(shù)
int nYear4 = nDays/FOURYEARS;//得到從1970年以來的周期(4年)的次數(shù)
int nRemain = nDays%FOURYEARS;//得到不足一個(gè)周期的天數(shù)
int nDesYear = 1970 + nYear4*4;
int nDesMonth = 0,nDesDay = 0;
bool bLeapYear = false;
if ( nRemain<365 )//一個(gè)周期內(nèi),第一年
{//平年
}
else if ( nRemain
{//平年
nDesYear += 1;
nRemain -= 365;
}
else if ( nRemain
{//平年
nDesYear += 2;
nRemain -= (365+365);
}
else//一個(gè)周期內(nèi),第四年,這一年是閏年
{//潤年
nDesYear += 3;
nRemain -= (365+365+365);
bLeapYear = true;
}
GetMonthAndDay(nRemain,nDesMonth,nDesDay,bLeapYear);
計(jì)算月份和日期的函數(shù):
static const int MON1[12] = {31,28,31,30,31};//平年
static const int MON2[12] = {31,29,31};//閏年
static const int FOURYEARS = (366 + 365 +365 +365);//每個(gè)四年的總天數(shù)
static const int DAYMS = 24*3600;//每天的毫秒數(shù)
void GetMonthAndDay(int nDays,int& nMonth,int& nDay,bool IsLeapYear)
{
int *pMonths = IsLeapYear?MON2:MON1;
//循環(huán)減去12個(gè)月中每個(gè)月的天數(shù),直到剩余天數(shù)小于等于0,就找到了對應(yīng)的月份
for ( int i=0; i<12; ++i )
{
int nTemp = nDays - pMonths[i];
if ( nTemp<=0 )
{
nMonth = i+1;
if ( nTemp == 0 )//表示剛好是這個(gè)月的最后一天,那么天數(shù)就是這個(gè)月的總天數(shù)了
nDay = pMonths[i];
else
nDay = nDays;
break;
}
nDays = nTemp;
}
}
3、附上C語言庫函數(shù)的實(shí)現(xiàn)
/****errno_t _gmtime32_s(ptm,timp) - convert *timp to a structure (UTC)
*
*Purpose:
* Converts the calendar time value,in 32 bit internal format,to
* broken-down time (tm structure) with the corresponding UTC time.
*
*Entry:
* const time_t *timp - pointer to time_t value to convert
*
*Exit:
* errno_t = 0 success
* tm members filled-in
* errno_t = non zero
* tm members initialized to -1 if ptm != NULL
*
*Exceptions:
*
*******************************************************************************/
errno_t __cdecl _gmtime32_s (
struct tm *ptm,const __time32_t *timp
)
{
__time32_t caltim;/* = *timp; *//* calendar time to convert */
int islpyr = 0; /* is-current-year-a-leap-year flag */
REG1 int tmptim;
REG3 int *mdays;/* pointer to days or lpdays */
struct tm *ptb = ptm;
_VALIDATE_RETURN_ERRCODE( ( ptm != NULL ),EINVAL )
memset( ptm,0xff,sizeof( struct tm ) );
_VALIDATE_RETURN_ERRCODE( ( timp != NULL ),EINVAL )
caltim = *timp;
_VALIDATE_RETURN_ERRCODE_NOEXC( ( caltim >= _MIN_LOCAL_TIME ),EINVAL )
/*
* Determine years since 1970. First,identify the four-year interval
* since this makes handling leap-years easy (note that 2000 IS a
* leap year and 2100 is out-of-range).
*/
tmptim = (int)(caltim / _FOUR_YEAR_SEC);
caltim -= ((__time32_t)tmptim * _FOUR_YEAR_SEC);
/*
* Determine which year of the interval
*/
tmptim = (tmptim * 4) + 70; /* 1970,1974,1978,...,etc. */
if ( caltim >= _YEAR_SEC ) {
tmptim++; /* 1971,1975,1979,etc. */
caltim -= _YEAR_SEC;
if ( caltim >= _YEAR_SEC ) {
tmptim++; /* 1972,1976,1980,etc. */
caltim -= _YEAR_SEC;
/*
* Note,it takes 366 days-worth of seconds to get past a leap
* year.
*/
if ( caltim >= (_YEAR_SEC + _DAY_SEC) ) {
tmptim++; /* 1973,1977,1981,etc. */
caltim -= (_YEAR_SEC + _DAY_SEC);
}
else {
/*
* In a leap year after all,set the flag.
*/
islpyr++;
}
}
}
/*
* tmptim now holds the value for tm_year. caltim now holds the
* number of elapsed seconds since the beginning of that year.
*/
ptb->tm_year = tmptim;
/*
* Determine days since January 1 (0 - 365). This is the tm_yday value.
* Leave caltim with number of elapsed seconds in that day.
*/
ptb->tm_yday = (int)(caltim / _DAY_SEC);
caltim -= (__time32_t)(ptb->tm_yday) * _DAY_SEC;
/*
* Determine months since January (0 - 11) and day of month (1 - 31)
*/
if ( islpyr )
mdays = _lpdays;
else
mdays = _days;
for ( tmptim = 1 ; mdays[tmptim] < ptb->tm_yday ; tmptim++ ) ;
ptb->tm_mon = --tmptim;
ptb->tm_mday = ptb->tm_yday - mdays[tmptim];
/*
* Determine days since Sunday (0 - 6)
*/
ptb->tm_wday = ((int)(*timp / _DAY_SEC) + _BASE_DOW) % 7;
/*
* Determine hours since midnight (0 - 23),minutes after the hour
* (0 - 59),and seconds after the minute (0 - 59).
*/
ptb->tm_hour = (int)(caltim / 3600);
caltim -= (__time32_t)ptb->tm_hour * 3600L;
ptb->tm_min = (int)(caltim / 60);
ptb->tm_sec = (int)(caltim - (ptb->tm_min) * 60);
ptb->tm_isdst = 0;
return 0;
}
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