localtime(), time(). What happened?

This is a discussion on localtime(), time(). What happened? within the C Programming forums, part of the General Programming Boards category; This is an example from my textbook. I was studying for an exam and after compiling a program I got ...

  1. #1
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    localtime(), time(). What happened?

    This is an example from my textbook. I was studying for an exam and after compiling a program I got surprising results. The book didn't mention it at all. Can anybody explain what happened?

    The output is:


    currentdate is Mon Dec 09 21:25:26 2002
    Tomorrow is 12/10/20102.
    0.05 seconds used by the processor.
    Press any key to continue
    Where did the 20102 come from??? What I don't know about time() then?

    And the code is:
    Code:
    #include <time.h>                                         
    #include <stdio.h>
    
    int main( void )
    {
        time_t t1;                                 
        struct tm *tptr;
        clock_t ticks;                             
        char *s;
    
        if ( ( t1 = time(( time_t * ) 0 )) != ( time_t )-1 ) {
            s = ctime( &t1 );
            printf( "currentdate is %s", s );
            tptr = localtime( &t1 );
            printf( "Tomorrow is %d/%d/20%d.\n",              
                                           tptr->tm_mon+1, 
                                           tptr->tm_mday+1,
                                           tptr->tm_year );
        }
        else
            printf( "Error with the time() function\n" );
    
                                                              
        if (( ticks = clock() ) != ( clock_t )-1 )
            printf( "%4.2f seconds used by the processor.\n",
                                      (double)ticks/CLK_TCK ); 
        else
            printf( "Error with the clock() function\n" );
        return 0;
    }
    Thanks

  2. #2
    Banned master5001's Avatar
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    Anyone can correct me if i'm wrong, but this reguards y2k. 99+1 = 100.

  3. #3
    drmauro223
    Guest
    It looks like the tm_year value represents number of years after 1900. Change it to:

    printf( "Tomorrow is %d/%d/%d.\n",
    tptr->tm_mon+1,
    tptr->tm_mday+1,
    1900 + tptr->tm_year );

  4. #4
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    tm_year is the number of years since 1900. so change 20%d to %d and instead of tm_year do 1900+tm_year

  5. #5
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    So you're saying that my textbook wasn't really updated (new edition 2002 and they didn't correct the code in the book... OK, thanks for explanation!

  6. #6
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    Maybe it is made for another OS?
    (I am not sure if that is just for *NIX or if Windows stores time like that too (does windows even use time_t and struct tm?))

  7. #7
    Banned master5001's Avatar
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    That code is windows compatible if that is what you were asking.

  8. #8
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    Originally posted by master5001
    That code is windows compatible if that is what you were asking.
    But does windows store tm_year has 1900 + tm_year?

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