[C++/wx]Custom Class with Default Parameter

[dodle]

I'm trying to create a custom wxDialog with an optional third argument (title). I thought that the correct way to do this was to use "=" to create a default value for the argument.

Here is a portion of my code:

gnrcabt.h

class GenericAbout : public wxDialog
{
public:
GenericAbout(wxWindow* parent, wxWindowID id, const wxString& title);
};

gnrcabt.cpp

GenericAbout::GenericAbout(wxWindow* parent, wxWindowID id, const wxString& title) : wxDialog(parent, id, title=_T("Default Title"))
{
}

test.cpp

about = new GenericAbout(this, -1);

Here is the error when I try to compile:

gnrcabt.cpp:3: error: passing `const wxString' as `this' argument of `wxString& wxString::operator=(const wxChar*)' discards qualifiers
I don't understand what the error is saying. But if I change "title=_T("Default Title")" to "title" in gnrcabt.cpp, and add a third argument, "title=_T("Custom Title")", to test.cpp everything works fine. But then the third argument is mandatory. What am I doing wrong?

[dodle]

Ok, figured it out. I set the default argument in the header file:

gnrcabt.h

class GenericAbout : public wxDialog
{
public:
GenericAbout(wxWindow* parent, wxWindowID id, const wxString& title=_T("Default Title"));
};