Adding #days to a date

So far I have this bit of code for adding number of days to a date using the time.h module:

Code:

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int main(int argc, char **argv)
{
        int numDays;
        printf ("Enter number of days to add ");
        scanf ("%d", &numDays);
        time_t now = time(NULL);
 
        struct tm* tm = localtime(&now);
 
        tm->tm_mday += numDays;
 
        cout << asctime(tm); 
       
        return 0;
}

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This works ok until you add 30 or more days to the date, then it'll give me something like>>September 53 2011<< if I add 40 days .

What have I done wrong??

Use mktime to normalise the values, so Sept 31 would become Oct 1.

This looks like C and not C++, so this thread is in the wrong section. For what reason did you put it here?

Quote:

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Originally Posted by Salem

Use mktime to normalise the values, so Sept 31 would become Oct 1.

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I've tried:

Code:

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cout << mktime(tm);

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But that gives the same results

Are you sure? mktime returns the day expressed as seconds from the epoch. You would have to take that result and make it into a string again with something like ctime().

umm.....

Code:

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#include <iostream>
#include <ctime>

int main(void){

        tm *tmptr = NULL;
        time_t now = time(NULL);
        int numdays;

        tmptr = localtime(&now);

        std::cout << "Current date/time is: "<<asctime(tmptr)<<std::endl;
        std::cout << "Enter number of days to add: ";
        std::cin >> numdays;

        tmptr->tm_mday += numdays; //add number of days
        mktime(tmptr);//normalize time ptr

        std::cout << numdays << " days later will be: "<<asctime(tmptr)<<std::endl;
       
        return(0);
}

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Thanks AndrewHunter your example works.
Strange though all I changed was this:

Code:

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struct tm* tm = localtime(&now);
 
        tm->tm_mday += numDays;
        mktime(tm);

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To this:

Code:

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tmptr = localtime(&now);
 
        tmptr->tm_mday += numDays;
        mktime(tmptr);

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