Thread: variable name prepended with L by compiler???

I'm checking out wxwidgets (I'm not sure if my problem has to do with it or not).

Code:

Window::Window (string &username) : wxFrame (NULL, mnID_MAIN, wxT("Mnote2"))
{
	wxBoxSizer *szr = new wxBoxSizer(wxVERTICAL);
	SetSizer(szr);

cerr << username << endl;

	this->status = new wxStatusBar(this, -1);
	szr->Add(this->status);

	wxString remoteuser = wxT(username.c_str());
	wxStaticText *user = new wxStaticText(this, -1, remoteuser);
	szr->Add(user);

}

The line in red causes this from g++:
mainwindow.cpp:15:1: error: ‘Lusername’ was not declared in this scope

What is that? There is no "Lusername" in the file at all. If I comment that line out, compiles fine and the cerr prints out username correctly. If I do this:

Code:

	string test("hello");
	wxString remoteuser = wxT(test.c_str());

I now get 'Ltest was not declared. WTF??

Originally Posted by threahdead

Can you find the definition of wxT? Might be a macro.

Yeah, and:

Code:

/* define wxT() and related macros */
/* ---------------------------------------------------------------------------- */

#if wxUSE_UNICODE
    /* use wxCONCAT_HELPER so that x could be expanded if it's a macro */
    #define wxT(x) wxCONCAT_HELPER(L, x)
#else /* !Unicode */
    #define wxT(x) x
#endif /* Unicode/!Unicode */

/*

Oh well. The wxWidgets docs and wiki actually do not say anything about how to convert from std::string, which is odd considering it is a C++ library.

Originally Posted by threahdead

Hm, i dont know the wxWidgets library. But it seems this does only work for char arrays.
You maybe could just do the assignment without the wxT() call.

No, that causes what the wiki explains is a unicode error. But there is a non-macro, wxString::FromAscii(), that works. Phew. The wx docs are mostly good but it is very silly that they do not just explain this at the top of the page for "wxString" instead of letting you shoot your foot and go running all over the web for half an hour. Grrrrr. Grrrr.

Everything is clearly explained in the documentary.

String functions

It is just a neat macro, which is to be used with string CONSTANTS. There exists an implicit conversion from std::string to wxString, but the problem is that you mix unicode and ansi. Note that you use unicode build for wxWidgets (because wxT expands to L) and std::string (ansi).

Of course, you can mix ansi and unicode, but you need to use a different constructor for wxString, and use std::string::c_str() explicitly:

wxString (the last one).

EDIT:

Yes, or the mentioned wxString::FromAscii()

Code:

‘Lusername’ was not declared in this scope

It's pronounced "Losername"

I haven't done much C++ lately, but if I remember correctly, putting L infront of a string makes it unicode. So you would do something like this:

Code:

std::wstring unicode = L"This is unicode";

Originally Posted by cpjust

Code:

‘Lusername’ was not declared in this scope

I haven't done much C++ lately, but if I remember correctly, putting L infront of a string makes it unicode.

Not quite. The L prefix makes the string literal wide, which means it is represented as an array of type wchar_t (which is an implementation defined wide character type). Unicode is a standardised character encoding. Unicode characters can be stored in a wchar_t, but a wchar_t is not necessarily unicode.