Question

I am now working on a some sort of a game engine and I had an idea to put everything engine-related into a static library and then link it to my actual problem.

Right now I achieved it and actually link that library and every functions seem to work fine, except those, which are windows-related.

I have a chunk of code in my library that looks like this:

   hWnd = CreateWindow(className, "Name", WS_OVERLAPPED | WS_CAPTION | WS_EX_TOPMOST,
              0, 0, 
              800, 600,
              NULL, NULL, GetModuleHandle(NULL), this);

   if (hWnd) {
      ShowWindow(hWnd, SW_NORMAL);
      UpdateWindow(hWnd);
   } else {
      MessageBox(NULL, "Internal program error", "Error", MB_OK | MB_ICONERROR);
      return;
   }

When this code was not in the library, but in the actual project, it worked fine, created the window and everything was ok. Right now (when I’m linking to my library that contains this code) CreateWindow(...) call returns NULL and GetLastError() returns “Operation succesfully completed” (wtf?).

Could anybody help me with this? Is it possible to create a window and display it using a static library call and why could my code fail?

Thank you.

Answer 1

Ah, maybe you’ve run into this problem described in an MSDN blog:

If you’re writing a static library, you may have need to access the HINSTANCE of the module that you have been linked into. You could require that the module that links you in pass the HINSTANCE to a special initialization function, but odds are that people will forget to do this.

If you are using a Microsoft linker, you can take advantage of a pseudovariable which the linker provides.

EXTERN_C IMAGE_DOS_HEADER __ImageBase;
#define HINST_THISCOMPONENT ((HINSTANCE)&__ImageBase)

The pseudovariable __ImageBase represents the DOS header of the module, which happens to be what a Win32 module begins with. In other words, it’s the base address of the module. And the module base address is the same as its HINSTANCE.

So there’s your HINSTANCE.

So, instead of passing GetModuleHandle(NULL) to CreateWindow, try ((HINSTANCE)&__ImageBase) (make sure it is declared as shown in the blog first).

Edit:

From the comments in that blog entry, one mentions the use of GetModuleHandleEx(), perhaps this is a more Compiler/Linker-agnostic approach.