How to compare two dates in C++Builder. 1 date from MaskEdit, 2 date from Date() - date

Question

I have to compare two dates.
The first one I get from the TMaskEdit component with the DD-MM-YYYY mask.
I get the second date from the Date() function.
I tried something like this:
String MaskEditDate = me3->Text.Trim();
String ActualDate = Date().FormatString("DD-MM-YYYY");
TDate TDMaskEditDate = StrToDate(MaskEditDate);
TDate TDActualDate = StrToDate(ActualDate);
if (TDMaskEditDate > TDActualDate)
{
ShowMessage("TDMaskEditDate > TDActualDate");
}
if (TDMaskEditDate == TDActualDate)
{
ShowMessage("TDMaskEditDate == TDActualDate");
}
if (TDMaskEditDate < TDActualDate)
{
ShowMessage("TDMaskEditDate < TDActualDate");
}
But, when I try to convert a string to a date, I get an error message like '2000-01-01' is not a valid date and I do not know why.

Answer 1

StrToDate() parses the input string according to the format specified by the global ShortDateFormat and DateSeparator formatting variables in the SysUtils unit. Those variables are initialized at app startup to your OS's current user locale. This is documented behavior in BCB's help file.
So clearly, one of the input strings you pass to StrToDate() does not match the format that your OS is using for dates, which is why you get the error.
To do what you are attempting, you would have to update those formatting variables to match the format used by your input (as the overloaded version of StrToDate() that takes a TFormatSettings as input did not exist yet in BCB6). And there is absolutely no reason to take a TDate from Date(), convert it to a String, and then parse it back into a TDate, that is just redundant.
Try this instead:
String MaskEditDate = me3->Text.Trim();
TDate TDActualDate = Date();
String oldShortDateFormat = ShortDateFormat;
Char oldDateSeparator = DateSeparator;
ShortDateFormat = "DD-MM-YYYY";
DateSeparator = '-';
TDate TDMaskEditDate = StrToDate(MaskEditDate);
ShortDateFormat = oldShortDateFormat;
DateSeparator = oldDateSeparator;
However, you really should not be using a T(Mask)Edit for date input anyway. A much safer option is to use the TDateTimePicker control instead. Set its Kind property to dtkDate and then read its Date property when needed. There is no need to process your date values using strings at all:
TDate TDDateTimePickerDate = DateTimePicker1->Date;
TDate TDActualDate = Date();
if (TDDateTimePickerDate > TDActualDate)
{
ShowMessage("TDDateTimePickerDate > TDActualDate");
}
else if (TDDateTimePickerDate == TDActualDate)
{
ShowMessage("TDDateTimePickerDate == TDActualDate");
}
else //if (TDDateTimePickerDate < TDActualDate)
{
ShowMessage("TDDateTimePickerDate < TDActualDate");
}
Alternatively:
#include <DateUtils.hpp>
TDate TDDateTimePickerDate = DateTimePicker1->Date;
TDate TDActualDate = Date();
switch (CompareDate(TDDateTimePickerDate, TDActualDate))
{
case GreaterThanValue:
ShowMessage("TDDateTimePickerDate > TDActualDate");
break;
case EqualsValue:
ShowMessage("TDDateTimePickerDate == TDActualDate");
break;
case LessThanValue:
ShowMessage("TDDateTimePickerDate < TDActualDate");
break;
}