Why is Listboxes not displaying elements using Visual C++ 6?

Question

So, I have a Listbox problem where the entries I want it to show are not being displayed in Visual C++ 6.

The code is as follows.

switch (m) {
    case WM_INITDIALOG: //To initiate the dialog box
    {
        HICON hicon = (HICON__ *)LoadImageW(GetModuleHandleW(NULL), MAKEINTRESOURCEW(IDI_ICONMAIN), IMAGE_ICON, 0, 0, LR_DEFAULTCOLOR | LR_DEFAULTSIZE);
        SendMessageW(h, WM_SETICON, ICON_BIG, (long)hicon);
        RECT Rect;
        ::GetWindowRect(h, &Rect);
        ::SetWindowPos(h, HWND_TOPMOST, (::GetSystemMetrics(SM_CXSCREEN)/2 - ((Rect.right - Rect.left)/2)), (::GetSystemMetrics(SM_CYSCREEN)/2 - ((Rect.bottom - Rect.top)/2)), (Rect.right - Rect.left), (Rect.bottom - Rect.top), SWP_SHOWWINDOW);
        //Place items in listbox.
        const std::string StringArray[] = {"10", "20", "30", "40", "50", "60", "70"};
        SendMessage(h, LB_ADDSTRING, DROPDOWN1, (LPARAM)StringArray);
        return TRUE;
    }

You are sending the message to the wrong window. Use descriptive variables names, "h" sucks. — Hans Passant, Feb 11 '16 at 21:09
@πάνταῥεῖ A quick google makes me think he means Visual C++ 6, but we can't be certain. — Silvio Mayolo, Feb 11 '16 at 21:10
@SilvioMayolo Well, I'm always playing possum for possums asking. I'm pretty sure there's an appropriate tag. — πάντα ῥεῖ, Feb 11 '16 at 21:10
You need to send the strings one by one, you cannot send an array like that. Win32 knows nothing about std::string so you need to send the raw c-string i.e. StringArray[i].c_str() — AndersK, Feb 11 '16 at 21:11
Where did you get the idea that you can use `LB_ADDSTRING` like that? `LB_ADDSTRING` requires a pointer to single zero-terminated string as `lparam`. You are sending a pointer to an *array*. And in addition to that the array contains `std::string` objects, which are not zero-terminated strings at all. — AnT stands with Russia, Feb 11 '16 at 21:53

score 1 · Accepted Answer · edited May 23 '17 at 12:30

C++ is not C#. Raw arrays are not classes and do not have methods.

Use std::vector< std::string >.

But before that, get a good C++ book and learn C++.

ETA Since you took out your edits where you were trying to call a non-existant .Length on the StringArray variable to traverse it in a for loop...

What in the MSDN documentation for the LB_ADDSTRING message makes you think it will accept a std::string? std::string is not a NULL terminated character array. Why would you think that you could cast an array of std::string to an LPARAM?

What you want is more like: (I have not compiled this code.)

typedef std::vector< std::string > string_vec;
const string_vec StringArray{"10", "20", "30", "40", "50", "60", "70"};

for( const auto & s : StringArray )
{
    SendMessage(h, LB_ADDSTRING, DROPDOWN1, (LPARAM)( s.c_str() ) );
}

Range-based for

N.B. this is modern C++, not ancient, obsolete VC++ 6.

Why is Listboxes not displaying elements using Visual C++ 6?

1 Answers1