Reading output from console program

Question

I need to read output from native C++ console application in my C++/.NET. There are many articles about this, but most wait until the process ends to read the output, which I don't want to, I need to read it immediately after it is "cout-ed" by the process (and don't want to block the GUI while doing so, but that's something I can do on my own). I tried two ways. One:

Diagnostics::Process ^process = gcnew Diagnostics::Process;
process->StartInfo->FileName = pathToExecutable;
process->StartInfo->RedirectStandardOutput = true;
process->StartInfo->UseShellExecute = false;
process->StartInfo->CreateNoWindow = true;
process->StartInfo->Arguments = "some params";
process->EnableRaisingEvents = true;
process->OutputDataReceived += gcnew Diagnostics::DataReceivedEventHandler( GUI::Form1::consoleHandler );
process->Start();
    process->BeginOutputReadLine();

And the handler:

    System::Void GUI::Form1::consoleHandler( System::Object^ sendingProcess, System::Diagnostics::DataReceivedEventArgs^ outLine ){
         GUI::Form1::contentForConsole += outLine->Data + "\n";
    }

But debugger confirmed it is called only after the process is finished.

On my second attempt I tried to create custom watching thread:

Diagnostics::Process ^process = gcnew Diagnostics::Process;
process->StartInfo->FileName = pathToExecutable;
process->StartInfo->RedirectStandardOutput = true;
process->StartInfo->RedirectStandardError = true;
process->StartInfo->UseShellExecute = false;
process->StartInfo->CreateNoWindow = true;
process->StartInfo->Arguments = "some params";

    processStatic = process; // static class member

process->Start();

System::Windows::Forms::MethodInvoker^ invoker = gcnew System::Windows::Forms::MethodInvoker(reader);
invoker->BeginInvoke(nullptr, nullptr);

And the thread function, it waits on the ReadLine function until the process finishes:

System::Void GUI::Form1::reader(){
    System::String^ str;
    while ((str = geogenProcess->StandardOutput->ReadLine()) != nullptr)
    {
        contentForConsole += str; // timer invoked handler then displays this, but this line is called only once the process is finished
    }   
}

The process executable ouputs many lines of text over time span ranging from several seconds to several minutes (depending on the actual task).

I'm interested in this too; we have a similar problem in our shop, though not in a critical location. — David Seiler
– David Seiler, Commented Oct 15, 2009 at 19:41

Matěj Zábský · Accepted Answer · 2009-10-17 14:37:41Z

1

I managed to find the answer myself in the end. Both ways of reading console output are perfectly functional. The problem was in the console application. I didn't know it is necessary to flush the console output manually to make it available to other apps.

So after replacing:

cout << "Some stuff " << some_var << " more stuff\n";

with

cout << "Some stuff " << some_var << " more stuff\n" << flush;

works like charm.

answered Oct 17, 2009 at 14:37

Matěj Zábský

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Comments

Dénes Tarján · Accepted Answer · 2009-10-16 07:35:36Z

0

Why don't redirect called process' output to a file and read that file from your program? If the child process flushes its output well, then you got a quite good response.

answered Oct 16, 2009 at 7:35

Dénes Tarján

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1 Comment

Matěj Zábský Over a year ago

The output file was written after the process finished as well.

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