Converting C headers to Delphi - Opaque Data Type

Question

During the conversion process I come across the following C code:

/** Opaque data type for the error object.
*/
typedef struct kError * KErrorRef;

Where is kError declared?

The conversion tool provided by Rudy Velthuis produces this code:

type
  {$EXTERNALSYM KErrorRef}
  KErrorRef = ^kError;

When I try to compile it, I get this error message:

[dcc32 Error] ukError.pas(50): E2003 Undeclared identifier: 'kError'

What is the appropriate way of converting the C code?

Answer 1

Where is kError declared?

Nowhere, because it is not actually needed.

In this declaration:

typedef struct kError * KErrorRef;

struct kError is an incomplete type, which is allowed when used with a pointer.

The declaration is roughly equivalent to this:

// forward declaration of some as-yet unknown struct type
struct kError;

// this is OK; compiler knows the size of a pointer, which is not
// affected by the size of the actual struct being pointed to
typedef kError *KErrorRef;

The conversion tool provided by Rudy Velthuis produces this code

The tool is not producing the correct Delphi code in this instance. When dealing with a typedef for an incomplete (forward-declared) struct type, it should produce Delphi code more like this instead, if the actual struct type is not declared later on:

type
  {$EXTERNALSYM KErrorRef}
  KErrorRef = ^kError;
  {$NODEFINE kError}
  kError = record
  end;