C date and time functions - Wikipedia

Now I am thinking of writing a program to let Guzunty Pi's LED driver to display time.  I don't know how the demo program gets the time data.  So I wikied.


C date and time functions - Wikipedia

http://en.wikipedia.org/wiki/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 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
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 Universal Coordinated 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.");
        return EXIT_FAILURE;
    }

    /* Convert to local time format. */
    c_time_string = ctime(&current_time);

    if (c_time_string == NULL)
    {
        (void) fprintf(stderr, "Failure to convert the current time.");
        return EXIT_FAILURE;
    }

    /* Print to stdout. */
    (void) printf("Current time is %s", c_time_string);
    return EXIT_SUCCESS;
}

The output is:

Current time is Sun Oct 28 12:30:37 2012

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