Thread: AdjustWindowRect/Setting client size

I know I've seen posted at least a couple times this link which gives an example of using AdjustWindowRect to set the client size to a specified width and height. But this doesn't appear to work correctly if the window has scrollbars. For example:

Code:

#include <windows.h>
#include <cassert>

void SetClientSize( HWND hwnd, int clientWidth, int clientHeight )
{
  if ( IsWindow( hwnd ) )
  {
    
    DWORD dwStyle = GetWindowLongPtr( hwnd, GWL_STYLE ) ;
    DWORD dwExStyle = GetWindowLongPtr( hwnd, GWL_EXSTYLE ) ;
    HMENU menu = GetMenu( hwnd ) ;
    
    RECT rc = { 0, 0, clientWidth, clientHeight } ;
    
    if(!AdjustWindowRectEx( &rc, dwStyle, menu ? TRUE : FALSE, dwExStyle ))
      MessageBox(NULL,"AdjustWindowRectEx Failed!","Error",MB_OK);
    
    SetWindowPos( hwnd, NULL, 0, 0, rc.right - rc.left, rc.bottom - rc.top,
                  SWP_NOZORDER | SWP_NOMOVE ) ;
#ifdef _DEBUG    
    RECT newClientRC;
    GetClientRect(hwnd,&newClientRC);
    assert((newClientRC.right-newClientRC.left)==clientWidth);
    assert((newClientRC.bottom-newClientRC.top)==clientHeight);
#endif
  }
}

LRESULT CALLBACK MainWindowProc (HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPreviousInstance,LPSTR lpcmdline,int nCmdShow)
{
  
	WNDCLASS wc;
	MSG msg;

	wc.style = CS_VREDRAW | CS_HREDRAW;
	wc.lpfnWndProc = MainWindowProc;
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hInstance = hInstance;
	wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
	wc.hCursor = LoadCursor (NULL, IDC_ARROW);
	wc.hbrBackground = (HBRUSH) (COLOR_SCROLLBAR + 1);
	wc.lpszMenuName = 0;
	wc.lpszClassName = "WinClassName";
  
	if (!RegisterClass (&wc))
		return 0;
  
  HWND hwnd;

	hwnd = CreateWindow (	"WinClassName",
							"AdjustWindowRect test",
							WS_OVERLAPPEDWINDOW|WS_VISIBLE|WS_VSCROLL|WS_HSCROLL,
							20,
							20,
							400,
							400,
							NULL,
							NULL,
							hInstance,
							NULL);

  if (!hwnd)
    return 0;
  SetClientSize(hwnd,500,500);
    while (GetMessage (&msg, NULL, 0, 0))
	{
		TranslateMessage (&msg);
		DispatchMessage (&msg);
	}
  return 0;
}

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

This gives an assertion error for me. It seems as though the scrollbars are counted as part of the client area for AdjustWindowRect, but not for GetClientRect. My solution was this:

Code:

void SetClientSize( HWND hwnd, int clientWidth, int clientHeight )
{
  if ( IsWindow( hwnd ) )
  {
    RECT winRC,clientRC;
    GetWindowRect(hwnd,&winRC); //get the current window rect
    GetClientRect(hwnd,&clientRC); //get the current client rect
    int dx = (clientRC.right-clientRC.left)-clientWidth; //calculate difference between current client width and desired client width
    int dy = (clientRC.bottom-clientRC.top)-clientHeight; //same for height
    //adjust the size
    SetWindowPos(hwnd,0,0,0,winRC.right-winRC.left-dx,winRC.bottom-winRC.top-dy,SWP_NOZORDER|SWP_NOMOVE);
#ifdef _DEBUG    
    RECT newClientRC;
    GetClientRect(hwnd,&newClientRC);
    assert((newClientRC.right-newClientRC.left)==clientWidth);
    assert((newClientRC.bottom-newClientRC.top)==clientHeight);
#endif
  }  
}

Which does not give an assertion error. Does anyone see any potential drawbacks to my solution, or have a reason for AdjustWindowRect to behave this way?

Edit: And this was built with VS 2003 if that makes a difference

Code:

    assert((newClientRC.bottom-newClientRC.left)==clientHeight)

bottom - left != height. Simple typo, change to bottom - top and see if that fixes it.
EDIT: Nevermind, that wasn't throwing errors for you anyways. (It would if height != width...)
EDIT: And I get the same results, oddly, for your first example. It's off by 16 pixels in either direction, the size of a scrollbar. Unless it counting that as client space...? You might get a scrollbars size with GetSystemMetrics() with SM_CHTHUMB (or SM_CVTHUMB)

Whoops, fixed the typo. I already knew that the client size wasn't correct, however, because it was causing problems in my program and I checked it in the debugger (for me it was off by 21)

Tricksey documentation...I need to learn to read more carefully (or maybe I was looking at the windows CE reference, which doesn't have that note)