Delphi assembler constant 'eof'

问题

There seems to be an undocumented constant eof in asm block context. This was tested using Delphi 7.

program TestEof;
{$APPTYPE CONSOLE}
var
  example : Integer;
begin
  asm
    mov example, eof
  end;
  writeln(example);
  readln;
end.

This prints out 14.

Where does that constant eof and it's value value $0E or 14 come from?

---

EDIT: this is the compilation result

...
call @InitExe
// mov example, eof
mov [example], $0000000e
// writeln(example)
mov eax, [$004040a4]
mov edx, [example]
call @Write0Long
call @WriteLn
call @_IOTest
// readln;
...

回答1:

Eof is in fact a function defined in the System unit.

In the implementations of Delphi that I have at hand, Delphi 6 and XE2, Eof is implemented as an intrinsic routine that results in a call to one of the following functions, as appropriate:

function _EofFile(var f: TFileRec): Boolean;
function _EofText(var t: TTextRec): Boolean;

I have no idea why your assembler code is turned into mov [...],$0000000e. You point out in a comment that the System unit itself makes use of eof in asm code, for example in TextOpen. The same code in XE2 is now pure Pascal and searches for a value of $1A instead of $0E. This would very much appear to be an implementation detail. If you want to understand why this is so then I think you will need to reverse engineer the code in the System unit, or see if the engineers at Embarcadero will explain the implementation to you.

来源：https://stackoverflow.com/questions/8702908/delphi-assembler-constant-eof