topic Re: Problem with "time" in C programming in Operating System - HP-UX

Problem with "time" in C programming

Henry Chua — Tue, 31 May 2005 08:41:14 GMT

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

Re: Problem with "time" in C programming

H.Merijn Brand (procura — Tue, 31 May 2005 08:49:55 GMT

# 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

Re: Problem with "time" in C programming

A. Clay Stephenson — Tue, 31 May 2005 08:54:00 GMT

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 */

Re: Problem with "time" in C programming

Henry Chua — Tue, 31 May 2005 20:29:09 GMT

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

Re: Problem with "time" in C programming

Nguyen Anh Tien — Tue, 31 May 2005 20:48:18 GMT

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

Re: Problem with "time" in C programming

Amit Agarwal_1 — Wed, 01 Jun 2005 00:22:12 GMT

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().

Re: Problem with "time" in C programming

Hein van den Heuvel — Wed, 01 Jun 2005 00:29:46 GMT

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.

Re: Problem with "time" in C programming

sw_5 — Wed, 22 Jun 2005 13:16:46 GMT

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

Re: Problem with "time" in C programming

sw_5 — Wed, 22 Jun 2005 13:19:58 GMT

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

Re: Problem with "time" in C programming

sw_5 — Wed, 22 Jun 2005 13:25:46 GMT

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

Re: Problem with "time" in C programming

A. Clay Stephenson — Wed, 22 Jun 2005 13:44:07 GMT

localtime() would never free the data structure. If localtime() is supplied a NULL pointer then it returns the address of a static variable that is reused upon each invocation of the function. In that case, it is imperitive to copy the values to other variable before calling localtime again. If a non-NULL pointer is supplied then localtime stores the value there and it is the responsibility of the calling program to then free any dynamically allowcated memory.

Re: Problem with "time" in C programming

Dennis Handly — Thu, 22 Dec 2011 12:48:25 GMT

>if you send in a non-null pointer to time()

You shouldn't do this because it causes the kernel to sweat. Just use the return result.

>If localtime() is supplied a NULL pointer

localtime(3) would probably abort on a NULL. Are you thinking of localtime_r?

>If a non-NULL pointer is supplied then localtime(3)

The input parm is of time_t*.