datetime - time difference's seems like working odd? -

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i going find difference between 2 times not getting want!!! have 2 timeedit components in form here code:

void __fastcall tform1::button1click(tobject *sender) {     ttime time1=strtotime(t1->text);     ttime time2=strtotime(t2->text);       //t1->text=time2-strtotime("3:00");      showmessage((time2-time1).timestring());    }

if set t1 = 02:00 , set t2 = 01:00

it shows 1:00

but expect 23:00 01:00 - 02:00 should 23:00

where wrong ?

you not taking account how ttime encoded. tdatetime double, integral portion contains number of days since dec 30 1899, , fractional portion contains percentage of 24-hour day (this information stated in c++builder documentation). ttime fractional portion of tdatetime integral portion ignored. because of encoding, performing such seemingly simple mathematical operations on date/time values not produce kind of result expecting.

02:00 (2 am) represented 0.083333333333, , 01:00 (1 am) represented 0.041666666667. subtracting 2 1 am, expecting subtract 2 hours produce 11 pm (which represented 0.958333333333333). subtracting 0.083333333333 0.041666666667 produces -0.041666666667. ignoring integral portion (the date), fractional portion positive value 0.0 (midnight), -0.041666666667 equivilent 0.041666666667, 1 am.

in order subtraction work correctly, starting time needs positive integral portion (date) attached result contains correct fractional portion, eg:

void __fastcall tform1::button1click(tobject *sender) {     ttime t = (1.0 + strtotime("01:00")) - strtotime("02:00");     // (1.0 + 0.041666666667) - 0.083333333333     // = 1.041666666667 - 0.083333333333     // = 0.95833333333     showmessage(t.timestring()); }

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