mktime()

[Sundar_7]

With very limited C skills, I have put together the following prog that takes the date as input and outputs the date in UNIX timestamp format.

I need this to test some password aging scripts we have.

But I cannot seem to get this working and mktime() always returns -1.

=============================================
#include
#include
main(int argc, char *argv[])
{
char *DAYS[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
char *MONTHS[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
int DATE,YEAR,HR,MIN,SEC,i,DAY,MTH,TIMEST;
char WDAY[10],MONTH[10];

strcpy(WDAY,argv[1]);
strcpy(MONTH,argv[2]);
DATE=atoi(argv[3]);
HR=atoi(argv[4]);
MIN=atoi(argv[5]);
SEC=atoi(argv[6]);
YEAR=atoi(argv[7]);

printf("Input to the Program: %s %s %d %d:%d:%d %d\n",WDAY,MONTH,DATE,HR,MIN,SEC,YEAR);

for(i=0;strcmp(DAYS[i],NULL)!= 0;i++)
{
if (strcmp(DAYS[i],WDAY) == 0)
DAY=i;
}

for(i=0;strcmp(MONTHS[i],NULL)!=0;i++)
{
if(strcmp(MONTHS[i],MONTH) == 0)
MTH=i+1;
}

YEAR=YEAR-1900;

printf("%d %d %d %d %d %d %d\n",SEC,MIN,HR,DATE,MTH,YEAR,DAY);

TIMEST=mktime(SEC,MIN,HR,DATE,MTH,YEAR,DAY,0,1);

printf("TIMESTAMP : %d\n",TIMEST);

}
==============================================

# cc some.c
# ./a.out Mon Sep 13 10 37 08 2004
Input to the Program: Mon Sep 13 10:37:8 2004
8 37 10 13 9 104 1
TIMESTAMP : -1
#

==============================================

what am I missing here ?

- Sundar

[Hein van den Heuvel · Accepted solution]

>>> what am I missing here ?

You should have opted for perl!

Seriously,
Check out 'man mktime'

You'll see the call takes only 1 argument, an array (ok, struct) containing those 9 arguments you passed.
You'll also see it tells you to '#include "
Do that. It declares 'struct tm' for you.

I'm sure you can take it from there....

Hein.

[A. Clay Stephenson]

Your fundamental problem is that mktime() expects a pointer to struct tm as an argument not a bunch of integers. You need to build up a struct tm and then send this in:

First declare a struct tm then populate it.

struct tm t;
time_t seconds = 0;

t.tm_sec = SEC % 61;
t.tm_min = MIN % 60;
t.tm_hour = HR % 24;
t.tm_mday = DATE % 32;
t.tm_mon = MTH - 1 /* 0 - 11 */
t.tm_year = YEAR; /* year - 1900 */
t.tm_wday = t.tm_yday = 0; /* ignored */
t.tm_isdst = -1; /* This will may the system decide */

seconds = mktime(&t);
(void) printf("%ld\n",seconds);

[Hein van den Heuvel]

oh... forgot to add. Check out recent topic:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=681997

It has some perl and shell code examples in this very area. (One of my replies there figures out time in seconds, just does nto print it).

Hein.

[Sundar_7]

Thanks for responding.

Yes, I understand mktime() accepts only the structure as the argument.

But I "based" my C prog on a perl excerpt that is listed on the URL

http://www.experts-exchange.com/Programming/Programming_Languages/Perl/Q_20090888.html

I didnt want to just copy and use the perl code since I dont understand PERL and wanted to write something similar in C, which I understand a little bit.

the perl code in the site seem to call mktime with bunch of integers( $timestamp = mktime($sec, $min, $hour, $date, $month, $year, $wday, 0, -1);) and it is working. Wondering why a similar call to mktime() from a C program returns -1 ?.

[Sundar_7]

hmm..I got this working, atlast :-)

============================================#include
#include
struct t_ptr
{
int SEC;
int MIN;
int HR;
int DATE;
int MTH;
int YEAR;
int DAY;
int YDAY;
int ISDST;
};

main(int argc, char *argv[])
{
char *DAYS[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
char *MONTHS[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
struct t_ptr t1;
int i,TIMEST;
char WDAY[10],MONTH[10];

strcpy(WDAY,argv[1]);
strcpy(MONTH,argv[2]);
t1.DATE=atoi(argv[3]);
t1.HR=atoi(argv[4]);
t1.MIN=atoi(argv[5]);
t1.SEC=atoi(argv[6]);
t1.YEAR=atoi(argv[7]);
t1.YDAY=0;
t1.ISDST=-1;

printf("Input to the Program: %s %s %d %d:%d:%d %d\n",WDAY,MONTH,t1.DATE,t1.HR,t1.MIN,t1.SEC,t1.YEAR);

for(i=0;strcmp(DAYS[i],NULL)!= 0;i++)
{
if (strcmp(DAYS[i],WDAY) == 0)
t1.DAY=i;
}

for(i=0;strcmp(MONTHS[i],NULL)!=0;i++)
{
if(strcmp(MONTHS[i],MONTH) == 0)
t1.MTH=i;
}

t1.YEAR-=1900;

printf("%d %d %d %d %d %d %d\n",t1.SEC,t1.MIN,t1.HR,t1.DATE,t1.MTH,t1.YEAR,t1.DAY);

TIMEST=mktime(t1);

printf("TIMESTAMP : %d\n",TIMEST);

}
============================================

But still not clear why call to mktime() with bunch of integers always return -1 where as a similar call in perl works ?

[Hein van den Heuvel]

Perl does NOT offer the system naked services.
There is no one-on-one mapping.
It just offers look-a-like, sound-a-like, do-a-like function with a perl flavor to it.

Building structure is trivial in C, hard in PERL. So Perl provides a structure-less interface.

fwiw, I consider your program broken. You have not passed a tm struct as you are supposed to, just something that happend to look an awfull lot like a struct tm. That's confusing, poor practice, error prone and requires additional work. The errors will happen when 'int' suddenly changes to 64 bit or 16 bit. When a port is done. When you moved on. 'they' will keep time.h honest. Noone will take are of you struct t_ptr or will know (at first glance) what it might stand for.

Just do that include time.h and use struct tm.

>> But still not clear why call to mktime() with bunch of integers always return -1 where as a similar call in perl works ?

That's the perl value-add. It tries to make life easy for most, at the price of confusing some.


Cheers,
Hein.

[Sundar_7]

Thanks Hein. I understand it is a poor practice to define my own structure instead of using existing one.

I am not a seasoned programmer neither there going to be a quality audit :-). Bottom line is, the above code gets the work done for me.

But yours and Clay's posts are educational, as always.

[Sundar_7]

See above.