C date and time functions

C date and time functions refer to a group of functions in the standard library of the C programming language implementing date and time manipulation operations. They provide support for time acquisition, conversion between date formats and formatted output to strings.

Overview of functions

The C date and time operations are defined in the time.h header file (ctime header in C++).

	Identifier	Description
Time manipulation	difftime	computes the difference between times
	time	returns the current time of the system as time since epoch (which is usually Unix epoch)
	clock	returns a processor tick count associated with the process
Format conversions	asctime	converts a tm object to a textual representation
	ctime	converts a tm object to a textual representation
	strftime	converts a tm object to custom textual representation
	wcsftime	converts a tm object to custom wide string textual representation
	gmtime	converts time since epoch to calendar time expressed as Universal Coordinated Time
	localtime	converts time since epoch to calendar time expressed as local time
	mktime	converts calendar time to time since epoch
Constants	CLOCKS_PER_SEC	number of processor clock ticks per second
Types	tm	calendar time type
	time_t	time since epoch type
	clock_t	process running time

Example

The following C source code snippet prints the current time to the standard output stream.

#include <stdio.h>
#include <time.h>

int main()
{
    /* Obtain current time as seconds elapsed since the Epoch. */
    time_t clock = time(NULL);
    
    /* Convert to local time format and print to stdout. */
    printf("Current time is %s", ctime(&clock));
    return 0;
}

The output is:

Current time is Sat Dec 31 11:20:45 2011