PRB: CWnd::GetWindowText(CString &) Asserts w/ Drop-Down Combo

The information in this article applies to:

• The Microsoft Foundation Classes (MFC), included with: Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51 and 1.52

SYMPTOMS

An attempt to call CWnd::GetWindowText(CString & rString) fails and an assertion occurs in STRCORE.CPP on line 336 if the CWnd object specifies a drop list combobox (a combobox with the CBS_DROPDOWNLIST window style).

The assertion in Visual C++ occurs on line 276 of STRCORE1.CPP.

CAUSE

The CWnd::GetWindowText(CString& ) function calls GetWindowTextLength(). If this function is called for a drop list ComboBox, Windows incorrectly returns -1 (CB_ERR). This is a bug in Windows. Because a CString can't have a length of -1, the application framework of MFC correctly displays an assertion.

RESOLUTION

To work around this problem, use the CWnd::GetWindowText(LPSTR, INT) function; it does not call GetWindowTextLength(). If you want to use a CString in your application, use code like the following:

   CString s;
   char* p = s.GetBuffer(10); // Allocate space for 10 characters.
   pComboBox->GetWindowText(p, 10);
   s.ReleaseBuffer();