How to resolve Delphi error: Incompatible types: 'PWideChar' and 'Pointer'

Question

I have this piece of code from Delphi 7:

var
  lpRgnData: PRgnData;
  PC: PChar;  
  PR: PRect;
  ...

  PC := @(lpRgnData^.Buffer[0]);

In Delphi XE4 it gives the following compile error:

Incompatible types: 'PWideChar' and 'Pointer'

How should this code be updated to work correctly in XE4?

Thanks

Answer 1

Whether or not this compiles depends upon the setting of the type-checked pointers option. You clearly have enabled that option which is an excellent decision. Doing so results in stricter type checking.

With type-checked pointers disabled, your code does compile. With type-checked pointers enabled, your code does not compile, which is what you want because your code is not valid.

Now, on to the types in question. They are defined in the Windows unit like this:

type
  PRgnData = ^TRgnData;
  {$EXTERNALSYM _RGNDATA}
  _RGNDATA = record
    rdh: TRgnDataHeader;
    Buffer: array[0..0] of Byte;
    Reserved: array[0..2] of Byte;
  end;
  TRgnData = _RGNDATA;
  {$EXTERNALSYM RGNDATA}
  RGNDATA = _RGNDATA;

The benefit of using type-checked pointers is that the compiler can tell you that what you are doing is not valid. It knows that lpRgnData^.Buffer[0] has type Byte and so @(lpRgnData^.Buffer[0]) has type ^Byte. And it knows that is not compatible with PChar which is an alias for PWideChar, that is ^WideChar.

Fix your code by changing the type of PC to ^Byte or PByte.