RAD Studio VCL Reference
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Enumerates floating point number types in the TTypeData record.
TFloatType = ( ftSingle, ftDouble, ftExtended, ftComp, ftCurr );
enum TFloatType { ftSingle, ftDouble, ftExtended, ftComp, ftCurr };
The GetTypeData routine utilises Delphi's RTTI (Run Time Type Information) to return a pointer to TTypeData record that describes a component property data type.
TTypeData is a variant record : the layout depends on the property TTypeKind value. When it is tkFloat, the data is one of the TFloatType enumerated values.
The TFloatType value meanings are as follows :
Value |
Meaning |
ftSingle |
Single data type. (-1.5 x 10^45 .. 3.4 x 10^38) |
ftDouble |
Double data type. (-5.0 x 10^324 .. 1.7 x 10^308) |
ftExtended |
Extended data type. (-3.6 x 10^4951 .. 1.1 x 10^4932) |
ftComp |
Comp data type. (-2^63+1 .. 2^63-1) |
ftCurr |
Currency data type. (20 significant digits, 4 decimal places) |
C++ Examples:
/* Add the Delphi source file that appears on this Help page into a CPP Builder project that includes a CPP module containing the following code. An hpp file will be generated for the Delphi code when you build the project. Add the include line for that hpp file at the top of the CPP module. The FormCreates for both forms will execute and the following generics code will work. Remember to give the forms different names! */ void __fastcall TForm1::FormCreate(TObject *Sender) { // Prints type info for string type TGenericClass__1<System::UnicodeString> *GString = new TGenericClass__1<System::UnicodeString>(); GString->PrintTypeInfo(Memo1); // Prints type info for Byte type TGenericClass__1<Byte> *GByte = new TGenericClass__1<Byte>(); GByte->PrintTypeInfo(Memo1); // Prints type info for Double type TGenericClass__1<Double> *GDouble = new TGenericClass__1<Double>(); GDouble->PrintTypeInfo(Memo1); // Prints type info for "array of String" type // TGenericClass__1<array of string> *GStringArray = new TGenericClass__1<array of string>(); // GStringArray->PrintTypeInfo(Memo1); }
Delphi Examples:
{ This example demostrates the methods to retreive of Run-time Type Information (RTTI) information. This example will print useful information about any given type including it's name, size, kind and sub-kind. } type TForm2 = class(TForm) Memo1: TMemo; procedure FormCreate(Sender: TObject); private { Private declarations } public { Public declarations } end; { Defining a generic type that contains a single class (static) method that will print information about the type it operates on. } TGenericClass<T> = class(TList<T>) // TList is a class in Generics.Collections public procedure PrintTypeInfo(memo: TMemo); end; TGenericString = class(TGenericClass<UnicodeString>) end; TGenericByte = class(TGenericClass<Byte>) end; TGenericDouble = class(TGenericClass<Double>) end; var Form2: TForm2; implementation {$R *.dfm} { Method defintition } procedure TGenericClass<T>.PrintTypeInfo(memo: TMemo); var Info : PTypeInfo; Data : PTypeData; KindName : String; SubName : String; begin { Get type info for the "yet unknown type" } Info := System.TypeInfo(T); { There is no RTTI attached for some types like Records for example. } if Info <> nil then begin memo.Lines.Add('Type name: ' + Info^.Name); { Find out the name of an enum item from it's ordinal value } KindName := TypInfo.GetEnumName(System.TypeInfo(TTypeKind), Ord(Info^.Kind)); memo.Lines.Add('Type kind: ' + KindName); Data := GetTypeData(Info); if Info^.Kind = tkInteger then begin { In case of integer let's see the actual sub-type name } SubName := TypInfo.GetEnumName(System.TypeInfo(TOrdType), Ord(Data^.OrdType)); memo.Lines.Add('Integer kind: ' + SubName); end; if Info^.Kind = tkFloat then begin { In case of float let's see the actual sub-type name } SubName := TypInfo.GetEnumName(System.TypeInfo(TFloatType), Ord(Data^.FloatType)); memo.Lines.Add('Float kind: ' + SubName); end; if Info^.Kind = tkDynArray then begin { Let's check out the element size } memo.Lines.Add('Array element type name: ' + Data^.elType^^.Name); memo.Lines.Add('Array element type size: ' + IntToStr(Data^.elSize)); end; end; memo.Lines.Add('Size of type: ' + IntToStr(SizeOf(T))); end; procedure TForm2.FormCreate(Sender: TObject); var GenericString : TGenericClass<UnicodeString>; GenericByte : TGenericClass<Byte>; GenericDouble : TGenericClass<Double>; // GenericStringArray : TGenericClass<array of string>; begin { Prints type info for string type} GenericString := TGenericClass<UnicodeString>.Create; GenericString.PrintTypeInfo(Memo1); { Prints type info for Byte type} GenericByte := TGenericClass<Byte>.Create; GenericByte.PrintTypeInfo(Memo1); { Prints type info for Double type} GenericDouble := TGenericClass<Double>.Create; GenericDouble.PrintTypeInfo(Memo1); end; { Expected results are: Type name: string Type kind: tkUString Size of type: 4 Type name: Byte Type kind: tkInteger Integer kind: otUByte Size of type: 1 Type name: Double Type kind: tkFloat Float kind: ftDouble Size of type: 8 Type name: .1 Type kind: tkDynArray Array element type name: string Array element type size: 4 Size of type: 4 }
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