Lesson 10 - Time Programming
10.1 Time Type
Codinated Universal Time (UTC): Coordinated Universal Time, which is known to everyone GMT (Greenwich Mean Time, GMT).
Calendar Time: calendar time, is "from a standard point in time (eg: at 0:00 on January 1, 1970) this number of seconds elapsed" to indicate the time.
10.2 Function Learning
There is a function of learning and learning methods before the same, that three-step learning method: function name; function prototypes; function uses.
1. Get a calendar time
(1) function name
time
(2) function prototype
time_t time(time_t *t);
(3) function-
Back to calendar time
(4) belongs to the header file
#include<time.h>
(5) Return value
Success: Time Calendar
Failure: -1
(6) Parameter Description
t: return value is not the case empty.
(7) sample program
#include<time.h>
void main()
{
time_t ctime;
ctime = time(NULL);
printf("ctime is %d\n",ctime);
}
2. Get GMT
(1) function name
gmtime
(2) function prototype
struct tm *gmtime(const time_t *timep);
(3) function-
Timep parameters specified calendar time grasping Huawei Standard Time.
(4) belongs to the header file
#include<time.h>
(5) Return value
strict tm
{
int tm_sec; //seconds
int tm_min; //minutes
int tm_hour; //hours
int tm_mday; //day of the month
int tm_mon; //month
int tm_year; //year
int tm_wday; //day of the week
int tm_yday; //day in the year
int tm_isdst; //daylight saving time
}；
Success: Coordinated Universal Time to struct tm stored in the form of
Failed: NULL
(6) Parameter Description
timep: with time into the world of
(7) sample program
#include<time.h>
void main()
{
time_t ctime;
struct tm *tm;
ctime = time(NULL);
// will be converted to standard time calendar time
tm = gmtime(&ctime);
printf("now is hour %d,min is %d\n",tm->tm_hour,tm->tm_min);
// Note that the method for the identification of structures in the body member.
}
3. Get the local time
(1) function name
localtime()
(2) function prototype
struct tm *localtime(const time_t *timep);
(3) function-
The parameters timep pointed calendar time into local time.
(4) belongs to the header file
#include<time.h>
(5) Return value
strict tm
{
int tm_sec; //seconds
int tm_min; //minutes
int tm_hour; //hours
int tm_mday; //day of the month
int tm_mon; //month
int tm_year; //year
int tm_wday; //day of the week
int tm_yday; //day in the year
int tm_isdst; //daylight saving time
}；
Success: returns the local time stored in the structure tm
Failed: NULL
(6) Parameter Description
timep: calendar time to be transformed
(7) sample program
#include<time.h>
void main()
{
time_t ctime;
struct tm *tm;
ctime = time(NULL);
// calendar time into local time
tm = localtime(&ctime);
printf("now is hour %d,min is %d\n",tm->tm_hour,tm->tm_min);
}
Note: To validate our program is correct, we can see the time by date command, and we will find the time to print out the above procedure is the same.
4. The string (format) displayed time
(1) function name
asctime
(2) function prototype
char *asctime(const struct tm *tm);
(3) function-
Struct tm is the time format into a string
(4) belongs to the header file
#include<time.h>
(5) Return value
Character string display time
(6) Parameter Description
tm: time format to be converted tm
(7) sample program
#include<time.h>
void main()
{
time_t ctime;
struct tm *tm;
char *stime;
ctime = time(NULL);
// calendar time into local time
tm = gmtime(&ctime);
printf("now is hour %d,min is %d\n",tm->tm_hour,tm->tm_min);
stime = asctime(tm);
printf("time is %s\n",stime);
}
The acquisition time precision
(1) function name
gettimeofday();
(2) function prototype
int gettimeofday(struct timeval *tv, strct timezone *tz);
(3) function-
Acquiring high precision time.
(4) belongs to the header file
#include<sys/time.h>
(4) Return value
Success: 0;
Failure: -1
(6) Parameter Description
struct timeval
{
time_t tv_sec; //seconds
Suseconds_t tv_usec; //microseconds
}
strutct timezone
{
int tz_minuteswest; //minutes west of Greewich
int tz_dsttime; //type of DST correction
}
tv: Save 0 from 1 January 1970: 0: 0 Number of seconds to go through here and microseconds;
tzone: usually NULL
(7) sample program
The following procedure is used to detect FUNC () function of time to run, here we use the header #include <stdio.h>, because this requires a NULL symbol header.
#include<sys/time.h>
#include<stdio.h>
void func()
{
int i,j;
int ret;
for(i=0;i<1000;i++)
for(j=0;j<1000;j++)
K = j;
}
void main()
{
int i,j;
struct timeval tv1;
struct timeval tv2;
gettimeofday(&tv1,NULL);
func();
gettimeofday(&tv1,NULL);
i = tv2.tv_sec-tv1.tv_sec;
j = tv2.tv_usec-tv1.tv_usec;
printf("sec is %d，usec is%d\n",i,j);
}
10.3 summary