On Monday 16 November 2009 08:59:50 Michael Van Canneyt wrote: > > It is nowhere written in the Delphi specs that const parameters > are passed by reference. It is often so, but is by no means guaranteed. > There is a sentence in Delphi 7 "Language Guide" in chapter 12 "Parameters and function results" which possibly belongs to the theme: http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/devcommon/programcontrolov_xml.html " Value and constant (const) parameters are passed by value or by reference, depending on the type and size of the parameter: [...] Sets, records, and static arrays of 1, 2, or 4 bytes are passed as 8-bit, 16-bit, and 32bit values. Larger sets, records, and static arrays are passed as 32-bit pointers to the value. An exception to this rule is that records are always passed directly on the stack under the cdecl, stdcall, and safecall conventions; the size of a record passed this way is rounded upward to the nearest double-word boundary. " An example from Delphi windows.pas: " type POverlapped = ^TOverlapped; _OVERLAPPED = record Internal: DWORD; InternalHigh: DWORD; Offset: DWORD; OffsetHigh: DWORD; hEvent: THandle; end; {$EXTERNALSYM _OVERLAPPED} TOverlapped = _OVERLAPPED; OVERLAPPED = _OVERLAPPED; {$EXTERNALSYM OVERLAPPED} [...] function LockFileEx(hFile: THandle; dwFlags, dwReserved: DWORD; nNumberOfBytesToLockLow, nNumberOfBytesToLockHigh: DWORD; const lpOverlapped: TOverlapped): BOOL; stdcall; " And the C++-header: " BOOL WINAPI LockFileEx( __in HANDLE hFile, __in DWORD dwFlags, __reserved DWORD dwReserved, __in DWORD nNumberOfBytesToLockLow, __in DWORD nNumberOfBytesToLockHigh, __inout LPOVERLAPPED lpOverlapped ); " So it is stdcall -> "An exception to this rule is that records are always passed directly on the stack" but LPOVERLAPPED is a pointer? There is a not documented special rule for const?
Please don't shot me if it does not belong to the theme. ;-) Martin _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
