window handle invalid

Hey all, just joined you.

Anyhow, I'm trying to run a simple windows program, and simply cannot figure out what I'm doing wrong. I remember doing this stuff about 3 years ago, but I don't remember any of it :/

Here's the code (there's more, but even this much doesn't work; I actually stole this from a tutorial online and it STILL doesn't work).

Code:

---


LRESULT CALLBACK WndProc( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
{ 
        switch(msg)
        {
                case WM_CLOSE:
                        DestroyWindow(hwnd);
                break;
                case WM_DESTROY:
                        PostQuitMessage(0);
                break;
                default:
                        return DefWindowProc(hwnd, msg, wParam, lParam);
        }
        return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
        LPSTR lpCmdLine, int nCmdShow)
{
        hwnd = CreateWindowEx(NULL, "ProgName", "First Program",WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, 0);

        if(hwnd == NULL)
        {
                MessageBox(NULL, "Window Creation Failed!", NULL,
                        MB_ICONEXCLAMATION | MB_OK);
                DWORD blah = GetLastError();
                return 0;
        }
        return 0;
}

---

It compiles and links just fine, but when the program executes the message box pops up and the application closes right after I click ok. When i run through it debugging, I look at the value of hwnd and find it to be 0x0.

Any help would be great! Thanks :)

> DWORD blah = GetLastError();
And the value of this would be what?

And then you look it up on MSDN

Whats your code for registering the window class?

Thanks salem, but I already tried that. the error code would be 0, which is not very helpful at all.

@DaveH
I was under the impression that if you did not specify a class, it would create a default. Either way, whether that's true or not, this code still did not work for me:

Code:

---

WNDCLASSEX wc;

wc.cbSize = sizeof(WNDCLASSEX);
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
wc.hInstance = hInstance;
wc.lpfnWndProc = WndProc;
wc.lpszClassName = "ProgName";
wc.lpszMenuName = NULL;
wc.style = 0;

---

Probably because you got the last error from your message box, not the API call which actually failed.

ah, good call salem, thanks. I just remembered to put this line in my code:

Code:

---

RegisterClassEx(&wc);

---

which was really stupid of me, sorry...

anyhow, it doesn't have a null window handle any more and the message box no longer pops up, but the window still doesn't show up. it just runs and quits without showing anything.

Quote:

---

Originally Posted by handle

ah, good call salem, thanks. I just remembered to put this line in my code:

Code:

---

RegisterClassEx(&wc);

---

which was really stupid of me, sorry...

anyhow, it doesn't have a null window handle any more and the message box no longer pops up, but the window still doesn't show up. it just runs and quits without showing anything.

---

RegisterClassEx was what I was looking for. Did you also

ShowWindow(...);
UpdateWidnow(...);

after creating the window?

Yes I did, but to no avail:

Code:

---


ShowWindow(hwnd,nCmdShow);
UpdateWindow(hwnd);

---

Well I decided to walk through the callback procedure...it went through the method 4 times.

1st time:
msg = 36 (WM_GETMINMAXINFO)

2nd time:
msg = 129 (WM_NCCREATE)

3rd time:
msg = 131 (WM_NCCALCSIZE)

4th time:
msg = 1 (WM_CREATE)

Then it doesn't go through the callback again. I step to the GetLastError, and it gives me error 87: "ERROR_INVALID_PARAMETER". Helpful. Where am I going wrong?

It is going to be very hard to tell what is going wrong unless we can see your all of the code.

You say you did ShowWindow, UpdateWindow but its not in your code you've show, so I have no idea where you do it.

Okay, to clarify everything here is the full code. Sorry I've been a little frazzled trying to get this fixed quickly :)

Code:

---


// win main
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
        LPSTR lpCmdLine, int nCmdShow)
{
        WNDCLASSEX wc;

        wc.cbSize = sizeof(WNDCLASSEX);
        wc.cbClsExtra = 0;
        wc.cbWndExtra = 0;
        wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
        wc.hCursor = LoadCursor(NULL, IDC_ARROW);
        wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
        wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
        wc.hInstance = hInstance;
        wc.lpfnWndProc = WndProc;
        wc.lpszClassName = "ProgName";
        wc.lpszMenuName = NULL;
        wc.style = 0;

        if(!RegisterClassEx(&wc))
        {
                MessageBox(NULL, "Window Registration Failed!", "Error!",
                        MB_ICONEXCLAMATION | MB_OK);
                return 0;
        }

        HWND hwnd = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW, "ProgName", "First Program",WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, 0);

        ShowWindow(hwnd,nCmdShow);
        UpdateWindow(hwnd);
        DWORD blah = GetLastError();
        if(hwnd == NULL)
        {
                MessageBox(NULL, "Window Creation Failed!", NULL,
                        MB_ICONEXCLAMATION | MB_OK);
                return 0;
        }
        return 0;
}

// and callback
LRESULT CALLBACK WndProc( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
{ 
        switch(msg)
        {
                case WM_CLOSE:
                        DestroyWindow(hwnd);
                break;
                case WM_DESTROY:
                        PostQuitMessage(0);
                break;
                default:
                        return DefWindowProc(hwnd, msg, wParam, lParam);
        }
        return 0;
}

---

And that should be everything I need to create a valid window correct? If not I am obviously missing something really simple.

You don't have a message loop. Just find the first random Win32 API tutorial in the internet and copy it from there.

Wow. I figured I was missing something stupid. Well, either way, now that I put that in there it doesn't quit automajically, but still no window shows up.

Thanks tho :)

(used this:)

Code:

---


while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }

---

The following code works for me. It displays a blank window. (this is your code, adding in the things you said you added, and adding variables etc. so it would compile.) I also added a definition for WndProc and moved your checking of the created window handle before the ShowWindow uses the handle.

Code:

---


#include "stdafx.h"
#include "resource.h"

LRESULT CALLBACK        WndProc(HWND, UINT, WPARAM, LPARAM);

// win main
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
        LPSTR lpCmdLine, int nCmdShow)
{
        MSG Msg;

        WNDCLASSEX wc;

        wc.cbSize = sizeof(WNDCLASSEX);
        wc.cbClsExtra = 0;
        wc.cbWndExtra = 0;
        wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
        wc.hCursor = LoadCursor(NULL, IDC_ARROW);
        wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
        wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
        wc.hInstance = hInstance;
        wc.lpfnWndProc = WndProc;
        wc.lpszClassName = "ProgName";
        wc.lpszMenuName = NULL;
        wc.style = 0;

        if(!RegisterClassEx(&wc))
        {
                MessageBox(NULL, "Window Registration Failed!", "Error!",
                        MB_ICONEXCLAMATION | MB_OK);
                return 0;
        }

        HWND hwnd = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW, "ProgName", "First Program",WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, 0);

        if(hwnd == NULL)
        {
                MessageBox(NULL, "Window Creation Failed!", NULL,
                        MB_ICONEXCLAMATION | MB_OK);
                return 0;
        }

        ShowWindow(hwnd,nCmdShow);
        UpdateWindow(hwnd);
        DWORD blah = GetLastError();
       

        while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }


        return 0;
}

// and callback
LRESULT CALLBACK WndProc( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
{ 
        switch(msg)
        {
                case WM_CLOSE:
                        DestroyWindow(hwnd);
                break;
                case WM_DESTROY:
                        PostQuitMessage(0);
                break;
                default:
                        return DefWindowProc(hwnd, msg, wParam, lParam);
        }
        return 0;
}

---