function StrToDateDef(const Value: String; UTC: Boolean=False;
DefaultValue: DateTime=DateTime(0)): DateTime
The StrToDateDef function converts the formatted local or UTC date string input parameter into its native value. The required format of the string is determined by the TFormatSettingsShortDateFormat property. If the input parameter is not a valid date string, the return value is the specified default value.
Examples
A := StrToDateDef('2/33/2012', StrToDate('1/1/2012'));
X := DateToStr(A); // X is '1/1/2012'