How to get the usable width of the window's main menu? - c++

Question

Say, I have a Win32 app with a menu added to the main window via CreateWindowEx method, and I need to know its usable width. The best way to illustrate the width I'm asking for is with this diagram:
So how do I calculate it?
When I try to do the following, it gives me the width of the client area:
MENUBARINFO mbi = {0};
mbi.cbSize = sizeof(mbi);
if(::GetMenuBarInfo(hWnd, OBJID_MENU, 0, &mbi))
{
int nUsableWifth = mbi.rcBar.right - mbi.rcBar.left;
}

Answer 1

If you want to know the width that is used for menu items, you can either:
use GetMenuItemRect() to get the screen coordinates of the last menu item, and then convert them to client coordinates within the parent window. The converted right edge coordinate will give you the width:
HMENU hMenu = ::GetMenu(hWnd);
int count = ::GetMenuItemCount(hMenu);
RECT r;
if (::GetMenuItemRect(hWnd, hMenu, count-1, &r))
{
::MapWindowPoints(NULL, hWnd, (LPPOINT)&r, 2);
int nUsedWidth = r.right;
...
}
the above assumes the menu starts at offset 0 within the window's client area. If you don't want to rely on that, you could instead get the screen coordinates of the 1st menu item and subtract it from the right-edge screen coordinate of the last menu item:
HMENU hMenu = ::GetMenu(hWnd);
int count = ::GetMenuItemCount(hMenu);
RECT rFirst, rLast;
if (::GetMenuItemRect(hWnd, hMenu, 0, &rFirst) &&
::GetMenuItemRect(hWnd, hMenu, count-1, &rLast))
{
int nUsedWidth = rLast.right - rFirst.left;
...
}
Either way, if you then want to know the width that is not used for menu items, simply get the menu's total width and subtract the above calculated width:
MENUBARINFO mbi = {0};
mbi.cbSize = sizeof(mbi);
if (::GetMenuBarInfo(hWnd, OBJID_MENU, 0, &mbi))
{
int nUsableWidth = (mbi.rcBar.right - mbi.rcBar.left) - nUsedWidth;
...
}
UPDATE: I didn't realize a window's menu can wrap its items vertically if the client area is too small to display them all on one line. In that case, you might have to do something more like this instead to calculate nUsedWidth:
HMENU hMenu = ::GetMenu(hWnd);
int count = ::GetMenuItemCount(hMenu);
int nUsedWidth = 0;
RECT r;
for(int idx = 0; idx < count; ++idx)
{
if (::GetMenuItemRect(hWnd, hMenu, idx, &r))
{
::MapWindowPoints(NULL, hWnd, (LPPOINT)&r, 2);
if (r.right > nUsedWidth)
nUsedWidth = r.right;
}
}
...
Or:
HMENU hMenu = ::GetMenu(hWnd);
int count = ::GetMenuItemCount(hMenu);
int nUsedWidth = 0;
RECT rFirst, r;
if (::GetMenuItemRect(hWnd, hMenu, 0, &rFirst))
{
nUsedWidth = rFirst.right - rFirst.left;
for (int idx = 1; idx < count; ++idx)
{
if (::GetMenuItemRect(hWnd, hMenu, idx, &r))
{
int nWidth = r.right - rFirst.left;
if (nWidth > nUsedWidth)
nUsedWidth = nWidth;
}
}
}
...