wxWidgets Visual Studio中的LINK问题

Question

I am trying to deal with wxWidgets for the first time, I tried to compile the below Hello World program:

/*
 * hworld.cpp
 */

#include "wx/wx.h" 

class MyApp: public wxApp
{
    virtual bool OnInit();
};

class MyFrame: public wxFrame
{
public:

    MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);

    void OnQuit(wxCommandEvent& event);
    void OnAbout(wxCommandEvent& event);

    DECLARE_EVENT_TABLE()
};

enum
{
    ID_Quit = 1,
    ID_About,
};

BEGIN_EVENT_TABLE(MyFrame, wxFrame)
    EVT_MENU(ID_Quit, MyFrame::OnQuit)
    EVT_MENU(ID_About, MyFrame::OnAbout)
END_EVENT_TABLE()

IMPLEMENT_APP(MyApp)

bool MyApp::OnInit()
{
    MyFrame *frame = new MyFrame( _("Hello World"), wxPoint(50, 50),
                                  wxSize(450,340) );
    frame->Show(true);
    SetTopWindow(frame);
    return true;
} 

MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
: wxFrame( NULL, -1, title, pos, size )
{
    wxMenu *menuFile = new wxMenu;

    menuFile->Append( ID_About, _("&About...") );
    menuFile->AppendSeparator();
    menuFile->Append( ID_Quit, _("E&xit") );

    wxMenuBar *menuBar = new wxMenuBar;
    menuBar->Append( menuFile, _("&File") );

    SetMenuBar( menuBar );

    CreateStatusBar();
    SetStatusText( _("Welcome to wxWidgets!") );
}

void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
{
    Close(TRUE);
}

void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
{
    wxMessageBox( _("This is a wxWidgets Hello world sample"),
                  _("About Hello World"),
                  wxOK | wxICON_INFORMATION, this);
}

The compiler showed:

Error   1   error LNK2001: unresolved external symbol _WinMainCRTStartup    C:\Users\550\documents\visual studio 11\Projects\wxWidgitExample\wxWidgitExample\LINK
Error   2   error LNK1120: 1 unresolved externals   C:\Users\550\documents\visual studio 11\Projects\wxWidgitExample\Debug\wxWidgitExample.exe  1

What is the problem ? I use MS Visual Studio, I guess I need to use #pragma directive?

Answer 1

Try putting wxDECLARE_APP(MyApp); in the header file where MyApp is defined and wxIMPLEMENT_APP(MyApp); in the cpp file where it is implemented. The description of these macros is avaliable in the documentation .

Answer 2

Check your property sheets under Linker->System->SubSystem. Make sure the subsystem is Windows and not Console.

Answer 3

That linker error you're getting usually indicates a mismatch in your project configuration settings between ansi vs unicode setup. If you're building your wxApplication with unicode enabled make sure UNICODE and _UNICODE are defined.

The entry point for a windows unicode application is wWinMainCRTStartup where as a non-unicode one has WinMainCRTStartup as its entry point. Normally wxWidgets should have that setup correctly for you when you built the framework.

To help troubleshoot your unresolved error I would try passing this switch to the linker when you attempt to build.

If you're example is not using unicode then use /ENTRY:WinMainCRTStartup .

If you're example is using unicode then use /ENTRY:wWinMainCRTStartup .