How do I detect if stdin or stdout is redirected in FreePascal under Windows?

问题

I need to know whether stdin or stdout has been redirected for a console application using the latest FPC (v3.0.0)

In the old Turbo Pascal days, I had a function written in assembly that did this. See below:

{ **************************************************************
  * Routine   : RedirectedStd                                  *
  * Purpose   : Return Yes (True) if standard handle is being  *
  *           : redirected.                                    *
  * Note(s)   : Even though handle can take any handle value,  *
  *           : the function will be meaningful only for the   *
  *           : standard input, standard output, and standard  *
  *           : error.  It will, however, be True for any      *
  *           : handle that does NOT point to the console.     *
  *           : (Besides, this is what it actually checks for.)*
  *           : Make sure handle belongs to an open file or    *
  *           : you will get wrong answer (check IOResult).    *
  ************************************************************** }
function RedirectedStd(handle: Word): Boolean; assembler;
const
  DEVICE       = $0080;
  FASTCONSOLE  = $0010;
  CONSOUT      = $0002;
  CONSIN       = $0001;
asm
  mov     InOutRes,0
  mov     ax,$4400       { IOCTL svc, get device information }
  mov     bx,handle
  int     $21            { result in DX }
  mov     ax,1           { assume function is True }
  jc      @Error         { got error with code in AX }
  test    dx,DEVICE
  jz      @Out
  test    dx,FASTCONSOLE
  jz      @Out
  test    dx,CONSOUT
  jz      @Out
  test    dx,CONSIN
  jz      @Out
  xor     ax,ax          { function is False }
  jmp     @Out
@Error:
  mov     InOutRes,ax
@Out:
end; { RedirectedStd }

This syntax is not valid for the FPC assembler. I tried my luck with the following variant which although compiles OK it crashes:

function RedirectedStd(handle: Word): Boolean; assembler;
label Error,Done;
const DEVICE       = $0080;
      FASTCONSOLE  = $0010;
      CONSOUT      = $0002;
      CONSIN       = $0001;
asm
          movw      $0,InOutRes
          movw      $4400,%ax           { IOCTL svc, get device information }
          movw      handle,%bx
          int       $21                 { result in DX }
          movw      $1,%ax              { assume function is True }
          jc        Error               { got error with code in AX }
          test      DEVICE,%dx
          jz        Done
          test      FASTCONSOLE,%dx
          jz        Done
          test      CONSOUT,%dx
          jz        Done
          test      CONSIN,%dx
          jz        Done
          xor       %ax,%ax             { function is False }
          jmp       Done
Error:    movw      %ax,InOutRes
Done:
end; { RedirectedStd }

(Not sure if my conversion is equivalent.)

Any ideas?

EDIT: Based on accepted answer which gave me enough direction to figure out the solution, I came up with the following drop-in replacement for my original routine:

function RedirectedStd(handle: Word): Boolean; {$ifndef WINDOWS} unimplemented; {$endif}
begin
  RedirectedStd := False;
  {$ifdef WINDOWS}
  case handle of
    0: RedirectedStd := GetFileType(GetStdHandle(STD_INPUT_HANDLE)) <> FILE_TYPE_CHAR;
    1: RedirectedStd := GetFileType(GetStdHandle(STD_OUTPUT_HANDLE)) <> FILE_TYPE_CHAR;
    2: RedirectedStd := GetFileType(GetStdHandle(STD_ERROR_HANDLE)) <> FILE_TYPE_CHAR;
  end;
  {$endif}
end; { RedirectedStd }

Oh, and you need to do Uses Windows;

回答1:

Use

GetFileType(GetStdHandle(STD_OUTPUT_HANDLE));

for stdout. It should be obvious what to do for stdin.

来源：https://stackoverflow.com/questions/40709193/how-do-i-detect-if-stdin-or-stdout-is-redirected-in-freepascal-under-windows

标签

freepascal

io-redirection