date difference problem

[ilyaw77]

Hi guys, I have a problem to calculate difference in date using difftime.
Two strings are passed to the function day1="05/01/2007" and day2="04/30/2007" the difference I got is 2 days which is wrong since there is no 31st day in april. The most surprising part I can pass 04/31/2007 ang get the right difference without any error while creating struct tm. What am I doing wrong?
Here is my programm:

 
int DaysDifference(string const& day1, string const& day2){
    int day,month,year;
    double diff;
 
    day=StrToInt(day1.substr(3,2));
    month=StrToInt(day1.substr(0,2));
    year=StrToInt(day1.substr(6,4))-1900;
    struct tm a= {0,0,12,day,month,year};
 
    day=StrToInt(day2.substr(3,2));
    month=StrToInt(day2.substr(0,2));
    year=StrToInt(day2.substr(6,4))-1900;
    struct tm b= {0,0,12,day,month,year};
 
    time_t x = mktime(&a);
    time_t y = mktime(&b);
    if ( x != (time_t)(-1) && y != (time_t)(-1) ){
        /*difftime returns difference in seconds*/
        diff = difftime(x,y)/(60*60*24);
    }
 
    return diff;
}
 
 

Thank you for the help

[ilyaw77]

Hey guys, I think I found my error, it should be:

month=StrToInt(day1.substr(0,2))-1;
 

thnaks a lot though !!! :)