C date and time functions
| C standard library |
|---|
| General topics |
| Miscellaneous headers |
The C date and time functions are a group of functions in the standard library of the C programming language implementing date and time manipulation operations.[1] 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 the epoch (which is usually the Unix epoch) | |
clock |
returns a processor tick count associated with the process | |
| Format conversions |
asctime |
converts a tm object to a textual representation (deprecated) |
ctime |
converts a time_t 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 the epoch to calendar time expressed as Coordinated Universal Time[2] | |
localtime |
converts time since the epoch to calendar time expressed as local time | |
mktime |
converts calendar time to time since the epoch | |
| Constants | CLOCKS_PER_SEC |
number of processor clock ticks per second |
| Types | tm |
calendar time type |
time_t |
time since the epoch type | |
clock_t |
process running time type |
Example
The following C source code snippet prints the current time to the standard output stream.
#include <time.h>
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
time_t current_time;
char* c_time_string;
/* Obtain current time as seconds elapsed since the Epoch. */
current_time = time(NULL);
if (current_time == ((time_t)-1))
{
(void) fprintf(stderr, "Failure to compute the current time.\n");
return EXIT_FAILURE;
}
/* Convert to local time format. */
c_time_string = ctime(¤t_time);
if (c_time_string == NULL)
{
(void) fprintf(stderr, "Failure to convert the current time.\n");
return EXIT_FAILURE;
}
/* Print to stdout. ctime() has already added a terminating newline character. */
(void) printf("Current time is %s", c_time_string);
return EXIT_SUCCESS;
}
The output is:
Current time is Wed Aug 20 17:53:49 2014
See also
References
- ^ ISO/IEC 9899:1999 specification (PDF). p. 351, § 7.32.2.
- ^ open-std.org - Committee Draft -- May 6, 2005 page 355
External links
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