How to Get Time and Date in C - C Program to Read and Display Time and Date

In this post, we will discuss how to read system time (current time) and date in c. To get system time and date, we use the time.h header file. It contains functions related to time and date. The function time() reads the current time and stores in the variable given as parameter. For example, if we call time(now), then the variable now is assigned the current date and time value. This parameter should be of type time_t. A sample code is:

time_t now;
time ( &now );

Note that we should pass the reference to a variable of type time_t.  But, the value stored by the function time() contains all information including date and time. So, the value appears to be an unintelligible random number. There fore, to extract hours, minutes, seconds, year, month, day of month etc from this value, we should convert into an object of structure struct tm. The function localtime() converts the value for us. This conversion to date and time can be done as follows:

Algorithm and C Program to Find Closure From Functional Dependencies

In this post we will see how to find closure of an attribute or a set of attributes. Before learning how to get closure, we should first know what is a closure. Closure of a given set C is the set of attributes that are functionally determined by the set C under the set of functional dependencies F. There can be closure for any set. Every attribute in the set whose closure is to be found out, will be a member of its closure set C⁺ also. Consider an example:

C Program to Show Process ID in Linux

This program is to show the process id (pid) in UNIX or Linx
The system call getpid() returns the process id of current process.

#include<stdio.h>
int main()
{
printf("\n Parent Process ID %d",getppid());
}

C Program to Display and Set System Time and Date Using 8086 Interrupts

This is a C Program to Display and Set System Time and Date Using 8086 Interrupts. Interrupt number 21 (in hexadecimal) is used to:

Output of c Program to get and set system time and date 

• Get System time
• Set System time
• Get System Date
• Set System Date

To Get system date:

- Call interrupt 0x21 (hexadecimal) 

- AH (higher byte of accumulator) should be made equal to 2A (hex) before calling interrupt

Output:

• day in DL
• Month in DH
• Year in CX

To set System Date:

- Call interrupt 0x21 (hexadecimal) 

- AH (higher byte of accumulator) should be made equal to 2B (hex) before calling interrupt

- Before Calling interrupt, store:

• Year in CX
• Month in DH
• Day in DL

To Get system time:

- Call interrupt 0x21 (hexadecimal) 

- AH (higher byte of accumulator) should be made equal to 2C (hex) before calling interrupt

Output:

• Hours in CH
• Minutes in CL
• Seconds in DH
• 1/100 th of a second in DL

To set System Time:







- Call interrupt 0x21 (hexadecimal) 

- AH (higher byte of accumulator) should be made equal to 2D (hex) before calling interrupt
- Before Calling interrupt, store:

Hour in CH 
Minutes in CL
Seconds in DH 
1/100 th of second in DL

#include<stdio.h>
#include<dos.h>
#include<conio.h>

void main()
 {
 int day,month,year,tflag=0,dflag=0,hr,min,sec;
 union REGS inreg,outreg;
DISDATE:printf("\nCurrent date:\n");
 inreg.h.ah=0x2a;
 int86(0x21,&inreg,&outreg);
 printf("%d-%d-%d ",outreg.h.dl,outreg.h.dh,outreg.x.cx);
 switch(outreg.h.al)
  {
  case 0:printf("Sunday");break;
  case 1:printf("Monday");break;
  case 2:printf("Tueday");break;
  case 3:printf("Wednesday");break;
  case 4:printf("Thursday");break;
  case 5:printf("Friday");break;
  case 6:printf("Sunday");break;
  }
 if(dflag==1)
  goto SETTIME;
DISTIME:printf("\nCurrent Time:\n");
 inreg.h.ah=0x2c;
 int86(0x21,&inreg,&outreg);
 printf("%d:%d:%d.%d ",outreg.h.ch,outreg.h.cl,outreg.h.dh,outreg.h.dl);
 if(tflag==1)
  goto END;
SETDATE:printf("\nSet Date.\nDay,Month and Year\n");
 scanf("%d%d%d",&day,&month,&year);
 inreg.h.ah=0x2b;
 inreg.x.cx=year;
 inreg.h.dh=month;
 inreg.h.dl=day;
 int86(0x21,&inreg,&outreg);
 if(outreg.h.al==0x00)
  {
  dflag=1;
  goto DISDATE;
  }
 else
  {
  printf("\nInvalid entry");
  getch();
  exit(0);
  }
SETTIME:printf("\nSet Time. Enter Time.\nHour,Minutes and Seconds\n");
 scanf("%d%d%d",&hr,&min,&sec);
 inreg.h.ah=0x2d;
 inreg.h.ch=hr;
 inreg.h.dh=sec;
 inreg.h.cl=min;
 inreg.h.dl=0;
 int86(0x21,&inreg,&outreg);
 if(outreg.h.al==0x00)
  {
  tflag=1;
  goto DISTIME;
  }
 else
  {
  printf("\nInvalid entry");
  getch();
  exit(0);
  }
END: getch();
 }