How to run a .exe program from matlab and pass console input as an argument?

Hello,

I'm trying to run a precompiled c++ program within a matlab project using the 'system()' function. Calling the c++ program is striaghtforward and works fine (see below).

system('Fourier.exe &');

The issue I'm having is within the c++ program itself, which uses the 'getch()' function and requires user input from the keyboard to continue at a certain point within the program. Altering the source code and recompiling the program is out of the scope of the project work. I am just trying to automate this script so it will call the program and continue automatically, without needing console input from the user. This would allow the program to run in the background without monitoring it.

Is there a way to pass a user input from the keyboard as an argument to the 'system()' function, so that way when the c++ program reaches the line where it requires user input, it will just continue?

I have also tried including '< nul' (below) but that doesnt work either. Any help would be greatly appreciated.

system('Fourier.exe < nul &');

Answer 1

[Walter Roberson]

You are using Windows. In the case of MATLAB for Windows, instead of using system() for this situation, use .NET methods System.Diagnostics.Process

https://www.mathworks.com/matlabcentral/answers/586706-how-to-redirect-standard-input-and-standard-output-using-net-system-diagnostics-process?s_tid=srchtitle

[Jonathan Chase]

In the case for this program, there are two times which a user needs to interact with the keyboard. Once at the beginning and then another time about halfway through. First I tried using the most basic attempt by getting the program to run using the tools you specified above as if I were using the system() command (that worked fine using this).

process = System.Diagnostics.Process();
process.StartInfo.FileName = 'Fourier.exe';
process.Start();

Next I tried passing input to the program but with no luck. It seems the program starts running, but when the command window pops up nothing happens and the matlab script does not continue. Here is what I wrote. Something must be off.

process = System.Diagnostics.Process();
process.StartInfo.FileName = 'Fourier.exe';
process.StartInfo.CreateNoWindow = false;
process.StartInfo.UseShellExecute = false;
process.StartInfo.RedirectStandardInput = true;
process.StartInfo.RedirectStandardOutput = true;

process.Start();
txt = '  ';
stdin = process.StandardInput;
stdin.Write(txt);
while(~process.HasExited)
    pause(1);
end
try
    process.Kill; % kill the process if needed.
catch
end

procss.Close();

[Walter Roberson]

It is not obvious to me that the Write() method is going to send a newline and it is not obvious to me that the process you are invoking is going to be operating character by character. But if it is operating character by character, then you might need to use the Flush() method.

[Jonathan Chase]

I do not know what you mean. Perhaps you could be more clear...

[Walter Roberson]

When you run the program interactively, is there action from the program as soon as you press the space key? Or is the action not until you press return?

If the action is not until you press return, then the program is using line-oriented reading, and is not notified of characters having been entered until a carriage return or new line are entered, at which point whatever had been typed so far would be forwarded to the program. In such a case, you would need to

stdin.Write(txt);
stdin.Write(newline);

or possibly

stdin.Writeline(txt);

If, however, the action is immediately upon pressing space, then the program is using single-character mode and does not need to be sent newline before it acts. However, for efficiency reasons, when you are dealing with streaming buffers between programs instead of dealing with keyboard I/O, at the time that you stdin.Write() what you Write() is not necessarily sent to the other side immediately. You might potentially need to

stdin.Flush()

to tell it to send what is in the buffers.

But sometimes none of these will work. Sometimes programs do not read from standard input, and instead connect directly to the keyboard drivers. If that happens to be the case for the executable you are dealing with, then anything you stdin.Write might simply be ignored by the executable. Potentially you might need to use the Java Robot class https://undocumentedmatlab.com/articles/gui-automation-robot

[Jonathan Chase]

Yes I see now, thank you for clarifying. This makes a lot of sense. To answer your question, the .exe continues on immediately after I hit the space bar.

Now I've updated the code slightly to include the Flush() method but it still does not write the space characters to the .exe. Seems like anything I give for standard input will not write to the command prompt when the .exe begins running.

process.Start();
txt = '  ';
stdin = process.StandardInput;
stdin.Write(txt);
stdin.Flush();
while(~process.HasExited)
    pause(1);
end
try
    process.Kill; % kill the process if needed.
catch
end
process.Close();

So I assume it is not going to read anything I give it using the standard input. Let me take a look at the link you provided.

Answer 2

[Jonathan Chase]

So I read up on some of the documentation you provided and ended up fixing the issue. As you mentioned the program wouldnt read any standard input. I solved the issue by invoking keyboard commands while within the Process loop.

process = System.Diagnostics.Process();
    process.StartInfo.FileName = 'Fourier.exe';
    process.Start();

    robot = java.awt.Robot;

    while(~process.HasExited)
        pause(10);
        robot.keyPress    (java.awt.event.KeyEvent.VK_SPACE);
        %
        robot.keyRelease  (java.awt.event.KeyEvent.VK_SPACE);
    
    end
    try
        process.Kill; % kill the process if needed.
    catch
    end

    process.Close(); 

Now the program is fully automated. Thank you for your time and for pointing me in the right direction.