Interfaces

What is translated > Types > Records, Classes, Interfaces > Interfaces

In Delphi interface types can be defined like in the following lines of code:

IConverter = interface

  ['{GUID}']

  function convert(Source : String): String;

end;

TConverter = class(TInterfacedObject, IConverter)

public

  //...

  function convert(Source : String): String;

end;  

For C++Builder the special macro "__interface" macro:

#define __interface struct  // in sysmac.h

is used instead of the class keyword  to mark interfaces:

__interface INTERFACE_UUID("{ GUID}" ) IConverter

{

  virtual String __fastcall convert(String Source);

};

class TConverter : public TInterfacedObject, public IConverter

{

  //...

  String __fastcall convert(String Source);

};

However there will be a linker error like "unresolved vtable", if such an interface is used. If you create a small pas file for the interface, add it to the C++Builder project and remove the C++ definition for the interface, C++Builder will create a header file for the interface file automatically, which you can include then. Example pas file:

unit Recyclable;

interface

 type

    IRecyclable = Interface(IInterface)

      function GetIsRecyclable : Boolean;

      property isRecyclable : Boolean read GetIsRecyclable;

    end;

implementation

end.

->

#include "Recyclable.hpp"

Now the project will compile without linker error.

Visual C++ also knows this keyword, but the GUID has to be written differently:

[ uuid( "GUID" ) ]

__interface IConverter

{

  virtual String convert(String Source);

};

class TConverter : public TInterfacedObject, IConverter

{

  //...

  String convert(String Source);

};

At other compilers, which have not the interface extension, multiple inheritance can be used instead, As explained here:

http://www.codeproject.com/Articles/10553/Using-Interfaces-in-C

the interface class needs a virtual destructor and the methods should be public and declared abstract:

//[ uuid( "GUID" ) ]

class IConverter

{

  public:

  virtual ~IConverter() {}

  virtual String convert(String Source) = 0;

};

class TConverter : public TInterfacedObject, IConverter

{

  //...

  String convert(String Source);

};

GUID's cannot be used here. Under Microsoft Windows GUID's are used for COM purposes.

This page belongs to the Delphi2Cpp Documentation