Question

I have been trying to capture stdout and stderr output from a DLL compiled in MSVC++ that my Delphi app statically links to, but so far have been unsuccessful.

procedure Test;
var
  fs: TFileStream;

begin
  fs := TFileStream.Create('C:\temp\output.log', fmCreate or fmShareDenyWrite);
  SetStdHandle(STD_OUTPUT_HANDLE, fs.Handle);
  SetStdHandle(STD_ERROR_HANDLE, fs.Handle);

  dllFunc(0); // Writes to stdout in MSVC++ console app, but not here
  // fs.Length is always zero

  fs.Free;
end;

Thought I was on the right track, but it does not work.

1. Is SetStdHandle() enough?
2. Is TFileStream the right thing to use here?
3. Am I using TFileStream properly for SetStdHandle()?
4. Is it possible that the DLL sets its stdout/stderr handles when the app loads? If so, where is the best place to use SetStdHandle() or equivalent?

Any help would be appreciated.

Answer 1

If the DLL grabs the stdout handles when it is loaded, then you will need to dynamically load the DLL after you have changed the stdout handles in your code.