DC not working

[shadybyte]

I want to use one of my programs to write on top of the window for another of my programs. I'll try to be as clear as I can. This is a sample of the code I used.

HANDLE hwindow;
HDC hdc;

if ((hwindow = FindWindow(NULL, TEXT("Target Window"))) != NULL) {
hdc = GetDC (hwindow);

TextOut (hdc, 0, 0, TEXT ("Hello Window"), 12);

ReleaseDC(hwindow, hdc);
}

Now I open the program with the caption "Target Window" and low and behold, the words "Hello Window" are no where to be seen. I am 100% sure that FindWindow() did find the window with the right caption. What I do not understand is this: What is the actual coordinate system (map mode) of hdc? Is hdc a device context for the whole window or for the window's client area, and whichever one it's for, how do I get the DC for the other? And most importantly of course, why do I not see the words "Hello Window" anywhere on top of the "Target Window"?

Thank you!

[fred100]

It's so basic that you have to read Petzold's book and painting part...

[shadybyte]

I'm sorry if I didn't find that statement to be at all helpful. Do you actually know what the problem is? At least point me to a specific topic --- "painting part" is very obscure, and who knows if I have that book.

[sjaycohn]

I want to use one of my programs to write on top of the window for another of my programs. I'll try to be as clear as I can. This is a sample of the code I used.

HANDLE hwindow;
HDC hdc;

if ((hwindow = FindWindow(NULL, TEXT("Target Window"))) != NULL) {
hdc = GetDC (hwindow);

TextOut (hdc, 0, 0, TEXT ("Hello Window"), 12);

ReleaseDC(hwindow, hdc);
}

Now I open the program with the caption "Target Window" and low and behold, the words "Hello Window" are no where to be seen. I am 100% sure that FindWindow() did find the window with the right caption. What I do not understand is this: What is the actual coordinate system (map mode) of hdc? Is hdc a device context for the whole window or for the window's client area, and whichever one it's for, how do I get the DC for the other? And most importantly of course, why do I not see the words "Hello Window" anywhere on top of the "Target Window"?

Thank you!

Where's the rest of your code?
This is not a complete program.
Where's the WinMain?
Where do you handle Windows messages?
This is what fred100 meant by needing Charles Petzold's book "Programming Windows".
I need to see how and where you create your window. Oh, you are writing to a window previously created.
Well, this is not a complete program anyway and I need to see more to help you.

[MrViggy]

Are you sure a valid handle was returned?

GetDC returns a DC to the window's client area, or NULL if it fails.

Viggy

[shadybyte]

The reason I'm sure that FindWindow() returns a valid handle is because I have other code in the statement below that does take place only when the "Target Window" exists.

if ((wnd = FindWindow (NULL, TEXT ("Target Window"))) != NULL) {
.........
.........
}

I am not close the computer that I work on at the moment, but I promise that messages are taken care of in a legitimate manner. But then again this code (which is the only thing that doesn't work) is very straightforward, I might be missing something rather important. So after being sure that FindWindow() did not return a NULL value, I call --- hdc = GetDC(wnd) --- immediately after, and then call the TextOut statement ---- TextOut (hdc, 0, 0, TEXT ("Hello Window"), 12) immediately after that. This is a very simple, yet unorthodox program, that tests the power that I can have over a window that I did not create. So I choose a target window, this window is simply a folder I created entitled "Target Window". When I open the folder (meaning the window now exists) everything happens except the TextOut statement. I would also like to know if I can cause the window (folder) to repaint itself among other things. (It's like having telepathic powers over another window, and would show how two programs can communicate uniquely)

[MrViggy]

Yes, but just because FindWindow returns a valid handle, that does not mean GetDC returns a valid DC.

Viggy

[shadybyte]

Wow, that's really nice to know! In which cases does this happen? That's definitely the root of my problem then.