Why multiCondition?

[Sander Bouwhuis]

I have many constructions like this in my code:

 1 case WM_COMMAND: // 0x111
 2   // What command message was sent?
 3   switch(HIWORD(wParam))
 4   {
 5     case CBN_SELENDOK: // 0x09
 6       // The user changed the selection of a combo box
 7       if(HWND(lParam) == m_hComboDsn)
 8         OnSelectDsn();
 9       else if(HWND(lParam) == m_hComboSite)
10         OnSelectSite();
11       else if(HWND(lParam) == m_hComboMember)
12         OnSelectMember();
13       else
14         return DefWindowProc(hWnd, u32Msg, wParam, lParam);
15       break;
16
17     default:
18       return DefWindowProc(hWnd, u32Msg, wParam, lParam);
19   }
20   break;

Everytime I get errors stating 'multiCondition':
line 9 : 'Expression is always false because 'else if' condition matches previous condition at line 7.
line 11 : 'Expression is always false because 'else if' condition matches previous condition at line 7.

In this case there are only 2 'else if' constructions, but if there are more I get errors for all of them.
Obviously, m_hComboDsn and m_hComboSite and m_hComboMember are different HWND handles.

Why is this error thrown?

[versat]

When usíng --platform=win64 i can reproduce these messages.
In the Cppcheck windows library configuration HWND is configured as a void pointer.
According to the debug output Cppcheck sees something like this:

if ( void * ( lParam ) == m_hComboDsn ) {
  OnSelectDsn ( ) ; }
else { if ( void * ( lParam ) == m_hComboSite ) {
  OnSelectSite ( ) ; }
else { if ( void * ( lParam ) == m_hComboMember ) {
  OnSelectMember ( ) ; }

I remember that i have created a ticket regarding these functional cast expressions some time ago: https://trac.cppcheck.net/ticket/8969
Maybe they still do not always work as they should.
If i surround the HWNDwith brackets (like this: if((HWND)(lParam) == m_hComboDsn) there are no strange warnings any longer.
I will try to create a useful ticket for this.

[versat]

I have created a ticket for this: https://trac.cppcheck.net/ticket/9307
Thanks for reporting

[Sander Bouwhuis]

So it has to do with the difference between a cast and a constructor?
cast : (HWND)lParam
constructor : HWND(lParam)

I always use the second notation, because almost all classes have a bunch of constructors, but not many classes have explicit cast functions.

[versat]

As far as i see it is not a constructor, it is just another kind of cast.
HWND is no class or struct as far as i know, so there is no constructor.
Looking into the Cppcheck code with Visual Studio it shows me that HWND is defined via

DECLARE_HANDLE            (HWND);

DECLARE_HANDLE is defined in the following way:

#define DECLARE_HANDLE(name) struct name##__{int unused;}; typedef struct name##__ *name

This expands to:

struct HWND__{int unused;}; typedef struct HWND__ *HWND;

So HWND is a pointer to a struct. Thus it has no constructor.
The Cppcheck configuration that tells Cppcheck that HWND is a void * is not completely wrong i would say. It should be useful for the analysis.
The issue is with the functional cast expression vs. a C-style cast expression.