No matching function for call (expects reference to pointer instead of pointer)

I get the error from xcode (3.2.4)/gcc(4.0):

/Users/admin/scm/audacity/mac/../src/toolbars/DeviceToolBar.cpp: In member function 'void DeviceToolBar::ShowInputDialog()':
/Users/admin/scm/audacity/mac/../src/toolbars/DeviceToolBar.cpp:817: error: no matching function for call to 'DeviceToolBar::ShowComboDialog(wxChoice*&, wxString)'
/Users/admin/scm/audacity/mac/../src/toolbars/DeviceToolBar.h:74: note: candidates are: void DeviceToolBar::ShowComboDialog(wxChoice*, wxString&)

So it looks like it expects a reference to a pointer in ShowComboDialog, but I don't know why as the signatures are clearly normal pointers. Furthermore if it was expecting a reference to a pointer the way I am calling it should work. This is the first error, and there are no special warnings before it.

Also, this compiles in MSVC 2008 express. 开发者_Python百科Please give me a clue.

//in the class def
//(only relevant portions included
class DeviceToolBar:public ToolBar {

 public:
   DeviceToolBar();
   virtual ~DeviceToolBar();
   void ShowInputDialog();
 private:
   void ShowComboDialog(wxChoice *combo, wxString &title);

   wxChoice *mInput;
};

//in the cpp file
void DeviceToolBar::ShowInputDialog()
{
   ShowComboDialog(mInput, wxString(_("Select Input Device")));
}

void DeviceToolBar::ShowComboDialog(wxChoice *combo, wxString &title)
{
//...
}

The problem is not the first parameter; its the second. You're passing in a temporary wxString, but the function is expecting a reference. C++ will automatically convert a temporary to a const reference, but it cannot convert it to a reference. You need to make ShowComboDialog take a const reference as its second parameter.

Your ShowComboDialog takes a wxString by non-const reference and you are trying to pass a temporary object as an argument to this parameter. You can only bind const references to temporary objects.

You either need to change ShowComboDialog to take its second argument either by value (wxString) or by const reference (const wxString&) or you need to create a variable for the wxString that you create when you call the function and then pass (a reference to) that variable instead.