How can I see cout output in a non-console application?

For a Windows solution, you can allocate a console, and bind cout/cin to it. For example:

AllocConsole();
freopen("CONOUT$", "w", stdout);
freopen("CONOUT$", "w", stderr);  

Documentation:
https://msdn.microsoft.com/en-us/library/windows/desktop/ms681944%28v=vs.85%29.aspx

To output a string to the debug console, use OutputDebugStringA. See http://msdn.microsoft.com/en-us/library/windows/desktop/aa363362%28v=vs.85%29.aspx

To output variable values to the debug console, using std::ostringstream, the send the string to OutputDebugStringA.

Excessive output statements will cause the program to severly slow down. However, it is a good technique to catch things the debugger has a problem with, such as the actual child members when playing with base pointers.

The question is very clear. How use std::cout to debug a non-console application in Visual Studio.

The answer is very clear: you cannot. That is, Visual Studio does not support std::cout as debug tool for non-console applications.

This is a serious limitation of Visual Studio, probably a failure to meet the C++ standard even. I find it very sad to see disinformative "answers" here trying to hide this defect of their precious Visual Studio.

SOLUTION: This answer solves the question and allows you to redirect console output to the Visual Studio Output window. First we need a class that overrides the default cout string stream:

class dbg_stream_for_cout
    : public std::stringbuf
{
public:
    ~dbg_stream_for_cout() { sync(); }
    int sync()
    {
        ::OutputDebugStringA(str().c_str());
        str(std::string()); // Clear the string buffer
        return 0;
    }
};
dbg_stream_for_cout g_DebugStreamFor_cout;

Then, somewhere you want to "activate" writing to the VS output window:

std::cout.rdbuf(&g_DebugStreamFor_cout); // Redirect std::cout to OutputDebugString!