Problem with "time" in C programming

[Henry Chua]

I see some syntax on a c program script which I dun quite understand...hope u guys can help..
Does this require "time.h"?
"
long now;
struct tm *c_time;

now= time(0);
c_time= localtime(&now); "

and what dictate the value of c_time and now?

Thanks in advance

[H.Merijn Brand (procura · Accepted solution]

# man 2 localtime

c_time is now a pointer to a struct that contains the broken down elements of the local time

The header file contains declarations of all relevant
functions and externals. It also contains the tm structure, which
includes the following members:

int tm_sec; /* seconds after the minute â [0,61] */
int tm_min; /* minutes after the hour â [0,59] */
int tm_hour; /* hours â [0,23] */
int tm_mday; /* day of month â [1,31] */
int tm_mon; /* month of year â [0,11] */
int tm_year; /* years since 1900 */
int tm_wday; /* days since Sunday â [0,6] */
int tm_yday; /* days since January 1 â [0,365] */
int tm_isdst; /* daylight savings time flag */

And strict ANSI wise that code isn't even good:

--8<---
#incluse
#include

:
:

time_t now;
struct tm *c_time;

now = time (0);
c_time= localtime (&now);

(void)printf ("Now: %02d-%02d-%04d %02d:%02d:%02d\n", c_time->tm_mday, c_time->tm_mon + 1, c_time->tm_year + 1900, c_time->tm_hour, c_time->tm_min, c_time->tm_sec);
-->8---

Enjo

[A. Clay Stephenson]

Yes you need #inclide and I don't like your use of 0 in place of NULL.

The time() function simply returns the number of seconds since 00:00:00 1-Jan-1970 UTC. If you send a NULL pointer to time the number of seconds is returned; if you send in a non-null pointer to time() the the value is stored in the variable pointed to.

int main()
{
timt_t now = 0;
struct tm *t = NULL;

now = time((time_t *) NULL);
t = localtime(&now);
(void) printf("Year: %d\n",t->tm_year + 1900);
return(0);
} /* main */

[Henry Chua]

Thanks for the info guys,

Just another question.. if my time(); = 1117524722, how can i decode them into ,year,month,day,hour,min,sec?

regards
Henry

[Nguyen Anh Tien]

Yes. Of course. You must include time.h lib.
pls refer my program as example
tienna

[Amit Agarwal_1]

You can use strftime(). You can print the date in the format of your choice. You will need to pass c_time as last argument to strftime().

[Hein van den Heuvel]

Henry,

Just re-read procura's reply. It's all there.

Now, instead of feeding now with time(), feed it your actual value!? (of course I would no longer call it 'now' but create a new time_t sometime; :-).

In quick perl examples:

# perl -e "print scalar localtime(1117524722)"
Tue May 31 03:32:02 2005

# perl -e "print join (',',localtime(1117524722))"
2,32,3,31,4,105,2,150,1
#


hth,
Hein.

[sw_5]

In addition, you can use mktime() to convert 1117524722 back to the year, month, etc.

[sw_5]

I have a question? All the samples about localtime() everywhere never free the struct. Could someone kindly let me know why?

c_time= localtime(&now);
delete c_time; // or use free for C

[sw_5]

Sorry, scrap the previous suggestion for using mktime(). That is for reverse-direction from year, mon -> time in seconds.