Read program STDIN in Delphi

Question

I have the following batch script:

dir | myapp.exe

And the program has this source (more or less):

procedure TForm1.FormCreate(Sender: TObject);
var buff: String;
begin
  Read(buff);
  Memo1.Lines.Text:=buff;
end;

And the output in the memo is:

Volume in drive C has no label.

I tried:

putting the read part into a loop with eof as a condition - somehow causing an infinite loop
writing a loop to keep reading until strlen(buff) is 0 - it exits the second time for some reason
reading stuff ever 0.5 seconds (I was thinking about asynchronous writes to stdin), this failed as well

By the way, running the program directly, without stdin data, causes an EInputOutput exception (I/O Error) code 6.

Rudy Velthuis · Accepted Answer · 2011-08-14 02:41:27Z

12

GUI apps don't have a stdin, stdout or stderr assigned automatically. You can do something like:

procedure TForm1.FormCreate(Sender: TObject);
var
  Buffer: array[0..1000] of Byte;
  StdIn: TStream;
  Count: Integer;
begin
  StdIn := THandleStream.Create(GetStdHandle(STD_INPUT_HANDLE));
  Count := StdIn.Read(Buffer, 1000);
  StdIn.Free;
  ShowMessageFmt('%d', [Count]);
end;

If you do

dir *.pas | myapp.exe

You'll see a messagebox with a number > 0, and if you do:

myapp.exe

You'll see a messagebox with 0. In both cases, the form will be shown.

edited Aug 14, 2011 at 2:41

answered Aug 14, 2011 at 2:21

Rudy Velthuis

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3 Comments

Christian Over a year ago

OK, that works nicely! Do I keep reading until Count<sizeOf(Buffer)?

Rudy Velthuis Over a year ago

Yes, just keep on reading until Count < Sizeof(Buffer). Note that buffer is not necessarily zero-terminated, so use e.g. a TMemoryStream to add the buffer to and finally add a #0 at the end, so you can read it as a string.

Rudy Velthuis Over a year ago

FWIW, although I answer questions here, I am mostly here to learn. Especially Objective-C, but also C, C++ and stuff like algorithms, etc.

Yahia · Accepted Answer · 2011-08-14 02:20:17Z

4

try using a stream approach instead Read(buff)

InputStream := THandleStream.Create(GetStdHandle(STD_INPUT_HANDLE));

answered Aug 14, 2011 at 2:20

Yahia

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