Undefined reference to WinMain@16 in C++

Question

i was taking the MSDN lesson for programming windows with C++ so i tried their code:

#ifndef UNICODE
#define UNICODE
#endif 

#include <windows.h>

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
// Register the window class.
const wchar_t CLASS_NAME[]  = L"Sample Window Class";

WNDCLASS wc = { };

wc.lpfnWndProc   = WindowProc;
wc.hInstance     = hInstance;
wc.lpszClassName = CLASS_NAME;

RegisterClass(&wc);

// Create the window.

HWND hwnd = CreateWindowEx(
    0,                              // Optional window styles.
    CLASS_NAME,                     // Window class
    L"Learn to Program Windows",    // Window text
    WS_OVERLAPPEDWINDOW,            // Window style

    // Size and position
    CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

    NULL,       // Parent window    
    NULL,       // Menu
    hInstance,  // Instance handle
    NULL        // Additional application data
    );

if (hwnd == NULL)
{
    return 0;
}

ShowWindow(hwnd, nCmdShow);

// Run the message loop.

MSG msg = { };
while (GetMessage(&msg, NULL, 0, 0))
{
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}

return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_DESTROY:
    PostQuitMessage(0);
    return 0;

case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        FillRect(hdc, &ps.rcPaint, (HBRUSH) (COLOR_WINDOW+1));

        EndPaint(hwnd, &ps);
    }
    return 0;

}
return DefWindowProc(hwnd, uMsg, wParam, lParam);

}

as i was compiling it as:

g++ -c app.cpp -s app.o
g++ -o app.exe app.o -s -Wl,--subsystem,windows 

then i get the error:

 undefined reference to WinMain@16

what's lacking?

Answer 1

Here is the correct code:

#ifndef UNICODE
#define UNICODE
#endif 

#include <windows.h>

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
// Register the window class.
const wchar_t CLASS_NAME[]  = L"Sample Window Class";

WNDCLASS wc = { };

wc.lpfnWndProc   = WindowProc;
wc.hInstance     = hInstance;
wc.lpszClassName = CLASS_NAME;

RegisterClass(&wc);

// Create the window.

HWND hwnd = CreateWindowEx(
    0,                              // Optional window styles.
    CLASS_NAME,                     // Window class
    L"Learn to Program Windows",    // Window text
    WS_OVERLAPPEDWINDOW,            // Window style

    // Size and position
    CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

    NULL,       // Parent window    
    NULL,       // Menu
    hInstance,  // Instance handle
    NULL        // Additional application data
    );

if (hwnd == NULL)
{
    return 0;
}

ShowWindow(hwnd, nCmdShow);

// Run the message loop.

MSG msg = { };
while (GetMessage(&msg, NULL, 0, 0))
{
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}

return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_DESTROY:
    PostQuitMessage(0);
    return 0;

case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        FillRect(hdc, &ps.rcPaint, (HBRUSH) (COLOR_WINDOW+1));

        EndPaint(hwnd, &ps);
    }
    return 0;

}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

Linker Settings

g++ -c app.cpp -s app.o -lgdi32 -lmingw32
g++ -o app.exe app.o -s -Wl,--subsystem,windows -lgdi32 -lmingw32

Answer 2

wWinMain should be WinMain....

Edit: Ok, so if you want to use the "wide" version of wWinMain, I expect you need to define -D_UNICODE so that the #include <windows.h> and other bits pick up the right parts. (Or edit the #define UNICODE to #define _UNICODE in your source, I suppose)