time_t

[Muthuveerappan]

Hi,

I have a doubt regarding time_t

I am initializing a time_t variable to 0.
When I display it, it shows "Thu Jan 1 07:30:00 1970" ?
I expected it to Thu Jan 1 00:0:00 1970 since t1 was initialized with 0

Pls let me know why this happens and how it can be rectified

Note:
Operating System - OS X (Mac)
Compiler - GCC

Given below is the code

/*

Aim - To set time_t variable to 01-Jan-1970 00:00:00
*/

#include <iostream>
#include <time.h>

int main()
{
    system("clear");


    time_t t1(0);
    
    std :: cout << "t1 = " << ctime(&t1) << std :: endl;                                                          
    
    //Why does this display "Thu Jan  1 07:30:00 1970" ?
    //I expected it to "Thu Jan  1 00:0:00 1970",  since t1 was initialized with 0
    
    

    return(0);
}

[itsmeandnobodyelse]

I assume you live in a time zone which is 7.30 hours away from GMT zone (London).


You may use functions like gmtime to get UCT times or use tzset to set your timezone accordingly.

[JohnW@Wessex]

That would put you on a longitude somewhere between Laos and the Philippines?

[Muthuveerappan]

Thanks a ton !! I wouldn't have guessed that in my dreams !!

Windows shows it as 8....

Strange it actually needs to be 8hrs .... not sure why it is 7:30 ... though the timezone is properly configured on the system.

Thanks again !!

[JohnW@Wessex]

Singapore?

[itsmeandnobodyelse]

Thanks a ton !! I wouldn't have guessed that in my dreams !!

Windows shows it as 8....

Strange it actually needs to be 8hrs .... not sure why it is 7:30 ... though the timezone is properly configured on the system.

Thanks again !!

You may check for the values in _timezone and _tzname[0], _tzname[1]. These global variables are declared in time.h.

[Muthuveerappan]

Thanks
------------
Thanks a lot !!

gmtime actually resolves the problem because it is the GMT time

I did check timezone, tzname[0], tzname[1], it doesn't show the correct names, but thats ok.

I guess gmtime should do it for me.

Question
---------------
I am new to this library, according to what i understand, time_t can only store upto the nearest second. Correct me if i am wrong

Is there a data type that is capable of storing milliseconds or is time_t capable of storing it ?

[JohnW@Wessex]

time_t is usually in seconds, which, in a 32 system, will cause a problem in the year 2038

1970 + 2^31 seconds = 2038. Sometime about the 18th January.

http://en.wikipedia.org/wiki/Year_2038_problem

[itsmeandnobodyelse]

Thanks
------------
Thanks a lot !!

gmtime actually resolves the problem because it is the GMT time

I did check timezone, tzname[0], tzname[1], it doesn't show the correct names, but thats ok.

I guess gmtime should do it for me.

Question
---------------
I am new to this library, according to what i understand, time_t can only store upto the nearest second. Correct me if i am wrong

Is there a data type that is capable of storing milliseconds or is time_t capable of storing it ?

Yes, it is timeb (or _timeb) structure that additionally contains milliseconds. Use ftime to get a timeb struct.

[D_Drmmr]

Is there a data type that is capable of storing milliseconds or is time_t capable of storing it ?

boost::posix_time::ptime

[Muthuveerappan]

Thanks a lot !!

Just feel timeb might be compiler specific (I could be completely wrong)

We are working on mac and windows... so i thought it would be better to use boost library (posix time).

the name posix worries me... if it would work on windows ....

hopefully it would work on windows as well.

[D_Drmmr]

hopefully it would work on windows as well.

It does.

[itsmeandnobodyelse]

Thanks a lot !!

Just feel timeb might be compiler specific (I could be completely wrong)

We are working on mac and windows... so i thought it would be better to use boost library (posix time).

the name posix worries me... if it would work on windows ....

hopefully it would work on windows as well.

ftime and timeb were available for any platform.

/* get local timestamp */
std::string getTimestampAsString(struct timeb* pTimB)
{
    char            szTimFmt[]      = "%Y%m%d %H%M%S";
    char            szTim[64]        = { '\0' };
    struct timeb    tim;            
    struct tm*      pTim            = NULL;

    /* get current time in milliseconds */
    if (pTimB == NULL)
        ftime(&tim);
    else
        memcpy(&tim, pTimB, sizeof(struct timeb));

    /* convert time part to local time  */
    pTim = localtime(&tim.time);
    /* convert to ascii                 */
    strftime(szTim, sizeof(szTim), szTimFmt, pTim);
    std::ostringstream oss;
    oss << szTim << "." << std::setw(3) << std::setfill('\0') << std::right << tim.millitm;
    return oss.str();
}