Controlling console applications

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Console windows and application output

During a "simple" project I discovered the tedious task of capturing the output of a console window into a control of the application. The additional difficulty was to hide the console window, thus hiding the application.

As it was to be expected, things were not as easy as redirecting output into a file and reading that file back in.

So I started creating a wrapper class for this task and it proved harder than it seemed at first. The provided sample in the MSDN did not mention the most important things and leaves more questions then it solves.

Searching around on various code sites shed some more light on the topic. Finally I could assemble a working solution. (Although there are some minor wishes left)

The CSpawn Class

This class has a pretty simple interface. A constructor, an execute function, an output function and finally a test to see if it is still active. The execute function and the output function are available in various flavours.

For the feedback you must derive a class from CSpawnConsumer and overload the Consume() function.

Usually it looks like this:

class CSpawnConsumer1 : public CSpawnConsumer
{
public:
    explicit CSpawnConsumer1(CMyEdit* pEdit)
                                   : m_pEdit(pEdit){}
    void Consume(TCHAR* p, DWORD dw)
    {
        m_pEdit->DoWhateverWithTheInput(p);
    }

private:
    CMyEdit* m_pEdit;
};

This class is called from the thread reading the output of the console window.

You can use the CSpawn class in two ways:

1. Using the constructor method CSpawn::CSpawn(CString& exe, CSpawnConsumer* sc)
2. Or creating a CSpawn variable and calling Execute(CString& exe, CSpawnConsumer* sc)

The default implementation will spawn the executable by resolving the ComSpec environment variable (normally CMD.EXE or COMMAND.EXE) and passing parameters to the given application.

You can provide user input to a running application by calling SendInput().

The Sample

The included sample project shows a simple edit control where any text entered is passed to the standard command interpreter and returns the results into the same edit control.

It shows how to interface with the CSpawn class in the most common way.

Compatibility

CSpawn was tested under Windows 2000 and Windows XP in Unicode and MBCS (both included in demo project) using Visual C++ 6.0 SP5 and MFC 6. Its not tested with .NET and MFC 7.

Revision History

19 Jun 2002 - Initial Revision

This article, along with any associated source code and files, is licensed under The Microsoft Public License (Ms-PL)