struct tm,time,localtime,mktime,ctime,gmtime,difftime,asctime,strftime

1. struct tm

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;

Member	Meaning	Range
tm_sec	seconds after the minute	0-61*
tm_min	minutes after the hour	0-59
tm_hour	hours since midnight	0-23
tm_mday	day of the month	1-31
tm_mon	months since January	0-11
tm_year	years since 1900
tm_wday	days since Sunday	0-6
tm_yday	days since January 1	0-365
tm_isdst	Daylight Saving Time flag

2. time      

Get current time

time_t time ( time_t * timer );

Example

/ *time example* /
#include <iostream>
#include <ctime>
using namespace std;


int main()
{
time_t seconds;
time(&seconds);
//或者seconds = time(NULL);
cout << seconds / 3600 << " hours since January 1,1970" << endl;

return 0;
}

Possible output:

3. localtime

<ctime>

struct tm * localtime ( const time_t * timer );

Convert time_t to tm as local time

Example

/*localtime example*/
#include <iostream>
#include <ctime>
using namespace std;


int main()
{
	time_t rawtime;
	struct tm* timeinfo;
	time(&rawtime);
	timeinfo = localtime(&rawtime);
	cout << "current local time and date: " << asctime(timeinfo);
	return 0;
}

Output:

4. mktime

time_t mktime ( struct tm * timeptr );

Convert tm structure to time_t

Example

/* mktime example: weekday calculator */
#include <iostream>
#include <ctime>
using namespace std;

int main()
{
	time_t rawtime;
	struct tm* timeinfo;
	int year,month,day;
	char* weekday[] = {
		"Sunday", 
		"Monday",
		"Tuesday", 
		"Wednesday",
		"Thursday",
		"Friday", 
		"Saturday"
	};
	
	cout << "Enter year: "; cin >> year;
	cout << "Enter month: "; cin >> month;
	cout << "Enter day: "; cin >> day;
	//将当前时间赋给rawtime
	time(&rawtime);
	//将rawtime转化为本地时间赋给timeinfo
	timeinfo = localtime(&rawtime);
	timeinfo->tm_year = year - 1900;
	timeinfo->tm_mon = month - 1;
	timeinfo->tm_mday = day;

	mktime(timeinfo);
	cout << "That day is a " << weekday[timeinfo->tm_wday] << endl;

	return 0;
}

Output:

5.ctime

<ctime>

char * ctime ( const time_t * timer );

Convert time_t value to string

Example

/*ctime example*/
#include <iostream>
#include <ctime>
using namespace std;

int main()
{
	time_t rawtime;
	time(&rawtime);
	cout << "Current local time is: " << ctime(&rawtime);

	return 0;
}

Output:

6. gmtime

<ctime>

struct tm * gmtime ( const time_t * timer );

Convert time_t to tm as UTC time

Example

/*gmtime example*/
#include <iostream>
#include <ctime>
using namespace std;

#define MST (-7)
#define UTC (0)
#define CCT (+8)

int main()
{
	time_t rawtime;
	struct tm * ptm;
	//将当前时间赋给rawtime
	time(&rawtime);cout << "time: " << rawtime << endl;
	//Convert time_t to tm
	ptm = gmtime(&rawtime);
	cout << "Current time around the World: ";
	cout << "Phoenix, AZ (U.S.): " << (ptm->tm_hour + MST) % 24
		<< ":" << ptm->tm_min << endl;
	cout << "Reykjavik (Iceland): " << (ptm->tm_hour + UTC) % 24
		<< ":" << ptm->tm_min << endl;
	cout << "Beijing (China): " << (ptm->tm_hour + CCT) % 24
		<< ":" << ptm->tm_min << endl;
	return 0;
}

Output:

7. difftime

<ctime>

double difftime ( time_t time2, time_t time1 );

Return difference between two times

Example

/*diifftime example*/
#include <iostream>
#include <ctime>
#include <string>
using namespace std;

int main()
{
	time_t start,end;
	string str;
	double dif;

	time(&start);
	cout << "Please input your name: ";
	cin >> str;
	time(&end);
	dif = difftime(end,start);
	cout << "Hi, " << str << "! It took you " << dif 
		<< "seconds to type your name. " << endl;

	return 0;
}

Output:

8. asctime

<ctime>

char * asctime ( const struct tm * timeptr );

Convert tm structure to string

Example

/* asctime example */
#include <iostream>
#include <ctime>
using namespace std;

int main()
{
	time_t rawtime;
	struct tm * timeinfo;
	time(&rawtime);
	timeinfo = localtime(&rawtime);
	cout << "Current date/time is: " << asctime(timeinfo);
	return 0;
}

Output:

9. strftime

<ctime>

size_t strftime ( char * ptr, size_t maxsize, const char * format,
                  const struct tm * timeptr );

Format time as string

specifier	Replaced by	Example
%a	Abbreviated weekday name *	Thu
%A	Full weekday name *	Thursday
%b	Abbreviated month name *	Aug
%B	Full month name *	August
%c	Date and time representation *	Thu Aug 23 14:55:02 2001
%d	Day of the month (01-31)	23
%H	Hour in 24h format (00-23)	14
%I	Hour in 12h format (01-12)	02
%j	Day of the year (001-366)	235
%m	Month as a decimal number (01-12)	08
%M	Minute (00-59)	55
%p	AM or PM designation	PM
%S	Second (00-61)	02
%U	Week number with the first Sunday as the first day of week one (00-53)	33
%w	Weekday as a decimal number with Sunday as 0 (0-6)	4
%W	Week number with the first Monday as the first day of week one (00-53)	34
%x	Date representation *	08/23/01
%X	Time representation *	14:55:02
%y	Year, last two digits (00-99)	01
%Y	Year	2001
%Z	Timezone name or abbreviation	CDT
%%	A % sign	%

Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

/* strftime example */ #include <stdio.h> #include <time.h> int main () { time_t rawtime; struct tm * timeinfo; char buffer [80]; time ( &rawtime ); timeinfo = localtime ( &rawtime ); strftime (buffer,80,"Now it's %I:%M%p.",timeinfo); puts (buffer); return 0; }

Example output:

Now it's 03:21PM.