Increment a date by 1 day?

This is a discussion on Increment a date by 1 day? within the C Programming forums, part of the General Programming Boards category; Hi I have been trying to figure out how to increment a datetime by 1 day. For example 2009-03-31 13:00:00. ...

  1. #1
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    Increment a date by 1 day?

    Hi
    I have been trying to figure out how to increment a datetime by 1 day. For example 2009-03-31 13:00:00. I managed to write the following code, but I almost knew before I ran it what would happen. It icrements the day to 32 which does not exist obviously.

    Code:
    #include <stdio.h>
    #include <time.h>
    
    int main()
    {
    
    time_t currentTime;
    time(&currentTime);
    struct tm *ptm = localtime(&currentTime);
    printf("%d\n",(ptm->tm_mday) +1);
    
    return 0;
    }
    Is there a way to convert a datetime to unix timestamp, add 86400 seconds, convert back to datetime?

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    Not tested, but you could add one to the tm_day member and run mktime (which I think is supposed to deal with odd things like the 32nd of January).

  3. #3
    Technical Lead QuantumPete's Avatar
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    You should be able to just add 86400 seconds to currentTime before you convert it to ptm. I haven't tested that yet though.

    QuantumPete
    "No-one else has reported this problem, you're either crazy or a liar" - Dogbert Technical Support
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  4. #4
    and the hat of wrongness Salem's Avatar
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    As tabstop suggests, use mktime() on what you're doing at the moment, and it will automatically normalise the time for you.

    So 32/01 becomes 01/02
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  5. #5
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    OK! mktime fixed it. Thanks for helping!

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