C++: How to set a new wndProc for a console application

access-deniedcconsolewinapiwndproc

If I have a console application with a handle to it set up like so;

HWND hWnd = GetConsoleWindow();

Then how do I set up a new wndProc for the window?
I tried using

SetWindowLong(hWnd, GWL_WNDPROC, (LONG)conProc);

With conProc being defined as

LRESULT CALLBACK conProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
        case WM_NCHITTEST:
            return HTCAPTION;
    }
    return DefWindowProc(hWnd, msg, wParam, lParam );
}

But it doesn't work and says "Error code: 5 – Access is denied" on GetLastError()

I understand that it's pretty difficult to modify the console application like this, since it's a csrss.exe application and all, but I'd still like to try..
Thanks.

Best Answer

While the impression is that console window belongs to your process (like other window), it is in fact hosted by CSRSS system process and its WndProc is there. This makes you unable to subclass the window and provide your own WndProc living in your process.

Some related reading:

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

C# – How to get the application’s path in a .NET console application

System.Reflection.Assembly.GetExecutingAssembly().Location¹

Combine that with System.IO.Path.GetDirectoryName if all you want is the directory.

¹As per Mr.Mindor's comment:
System.Reflection.Assembly.GetExecutingAssembly().Location returns where the executing assembly is currently located, which may or may not be where the assembly is located when not executing. In the case of shadow copying assemblies, you will get a path in a temp directory. System.Reflection.Assembly.GetExecutingAssembly().CodeBase will return the 'permanent' path of the assembly.