CODEWITHSUNDEEP
delphidelphi-xe8
user4855729
user4855729

Reputation: 147

Porting C union

I am trying to port a C structure which has a union inside. The default structure in Winapi.Winsock2.pas is missing some fields in the record. But is this the correct way? Thanks.

typedef struct _WSACOMPLETION {
  WSACOMPLETIONTYPE Type;
  union {
    struct {
      HWND   hWnd;
      UINT   uMsg;
      WPARAM context;
    } WindowMessage;
    struct {
      LPWSAOVERLAPPED lpOverlapped;
    } Event;
    struct {
      LPWSAOVERLAPPED                    lpOverlapped;
      LPWSAOVERLAPPED_COMPLETION_ROUTINE lpfnCompletionProc;
    } Apc;
    struct {
      LPWSAOVERLAPPED lpOverlapped;
      HANDLE          hPort;
      ULONG_PTR       Key;
    } Port;
  } Parameters;
} WSACOMPLETION;

_WSACOMPLETION = record
  &Type: WSACOMPLETIONTYPE;
  case Parameters: Integer of
    0: (hWnd: HWND; uMsg: UINT; context: WPARAM); // WindowMessage
    1: (lpOverlapped: LPWSAOVERLAPPED); // Event
    2: (lpOverlapped: LPWSAOVERLAPPED; lpfnCompletionProc: LPWSAOVERLAPPED_COMPLETION_ROUTINE); // Apc
    3: (lpOverlapped: LPWSAOVERLAPPED; hPort: HANDLE; Key: ULONG_PTR); //Port
end;

The compiler complains with Error: E2004 Identifier redeclared: 'lpOverlapped'

UPDATE 2:

After some thinking I've come up with this. 

  _WSACOMPLETION = record
    &Type: WSACOMPLETIONTYPE;
    case Parameters: Integer of
    0: (WindowMessage: record
        hWnd: HWND;
        uMsg: UINT;
        context: WPARAM;
          end);
    1: (Event: record
        lpOverlapped: LPWSAOVERLAPPED;
         end);
    2: (Apc: record
                lpOverlapped: LPWSAOVERLAPPED;
                lpfnCompletionProc: LPWSAOVERLAPPED_COMPLETION_ROUTINE
       end);
    3: (Port: record
        lpOverlapped: LPWSAOVERLAPPED;
        hPort: HANDLE;
        Key: ULONG_PTR;
         end)
  end;

Upvotes: 2

Views: 186

Answers (1)

David Heffernan
David Heffernan

Reputation: 613352

Your translation is fine, modulo the fact that you have to use a separate name for each of the members of the record.

Personally though, I would define a record for each branch of the union. That would allow you to give each branch of the union a name, as is the case in the C code.

Upvotes: 1

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