C date and time operations

C Standard Library
Data types Character classification Strings Mathematics File input/output Date/time Localization Memory allocation Program control Miscellaneous headers: <assert.h> <errno.h> <iso646.h> <setjmp.h> <signal.h> <stdarg.h> <wchar.h>
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C date and time operations refer to a group of functions in the standard library of the C programming language implementing date and time manipulation operations.^[1]

Function overview

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

Time manipulation

difftime - computes the difference between times

time - returns the current time of the system as time since epoch

clock - returns raw processor clock time since the program is started

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

This source code snippet prints the current time to the standard output stream.

#include <stdio.h>
#include <time.h>
 
int main(void)
{
    time_t timer = time(NULL);
    printf("current time is %s", ctime(&timer));
    return 0;
}
 
/*
Output is:
current time is Mon Oct 24 17:57:45 2011
*/

References

1. ^ ISO/IEC 9899:1999 specification. p. 351, § 7.32.2. http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf. 

External links