winMain error C++

Question

winMain error C++

Komissarov Maxim 41

I wrote a simple app code using WINAPI. Visual Studio detects no errors but while building appears an error of "external symbol". Unresolved external symbol WinMain referenced in function "int __cdecl invoke_main(void)" (?invoke_main@@YAHXZ);

here's the code:

include "windows.h"

LRESULT CALLBACK wndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

int WINAPI winMain(In HINSTANCE hInst, _In_opt_ HINSTANCE hPrevInst, In LPSTR lpCmdLine, In int nCmdShow) {
TCHAR zcClassName[] = L"Window Class";
HWND hMainWnd;
MSG msg;
WNDCLASSEX wndClass;

wndClass.cbSize = sizeof(wndClass);  
wndClass.style = CS_HREDRAW | CS_VREDRAW;  
wndClass.lpfnWndProc = wndProc;  
wndClass.lpszMenuName = NULL;  
wndClass.lpszClassName = zcClassName;  
wndClass.cbWndExtra = NULL;  
wndClass.cbClsExtra = NULL;  
wndClass.hIcon = LoadIcon(NULL, IDI_WINLOGO);  
wndClass.hIconSm = LoadIcon(NULL, IDI_WINLOGO);  
wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);  
wndClass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);  
wndClass.hInstance = hInst;  

if (!RegisterClassEx(&wndClass)) {  
    MessageBox(NULL, L"Class Not Registered", L"FATAL ERROR", MB_OK);  
    return NULL;  
}  

hMainWnd = CreateWindow(zcClassName, L"Test Program", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, NULL, CW_USEDEFAULT, NULL, (HWND)NULL, NULL, HINSTANCE(hInst), NULL);  

ShowWindow(hMainWnd, nCmdShow);  
UpdateWindow(hMainWnd);  
while (GetMessage(&msg, NULL, NULL, NULL)) {  
    TranslateMessage(&msg);  
    DispatchMessage(&msg);  
}  
return msg.wParam;

}

LRESULT CALLBACK wndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {
switch (msg) {
case WM_CREATE:
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return wndProc(hWnd, msg, wParam, lParam);
}
}

why isn't it compiling?

RLWA32 49,636 Reputation points

2022-11-23T00:01:34.833+00:00

why isn't it compiling?

The code does compile (with warning messages that should not be ignored). The error is a linker error. See below for the solution to this problem.
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2022-11-23T02:18:47.197+00:00

@Komissarov Maxim

I agree with RLWA32-6355:

1, You should use WinMain instead of winMain.

2, You should use return DefWindowProc(hWnd, msg, wParam, lParam); instead of return wndProc(hWnd, msg, wParam, lParam);

For more details I suggest you could refer to the Docs:

Module 1. Your First Windows Program

WinMain function

DefWindowProcA function
Sawyer261 1 Reputation point

2022-11-23T03:10:21.047+00:00

As the coding of WINAPI. Visual Studio was showing the same issue to for Best electric bike app. Then I fully converted the coding to the html and custom coding through simple using the notepad ++ and carefully checked each and every loop of the code. Which is now working fine for all the platforms. So kindly check their will be a loop which will be stopping it.
Komissarov Maxim 41 Reputation points

2022-11-24T17:15:00.033+00:00

Thank you! This helped a lot
RLWA32 49,636 Reputation points

2022-11-24T17:32:30.617+00:00

You may also find it helpful to create a New Project with Visual Studio's template for a Windows Desktop Application. It will create a fully formed project including a menu and resources. Its also a good starting point for learning.

Accepted answer

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RLWA32 49,636 Reputation points

2022-11-23T00:01:34.833+00:00

why isn't it compiling?

The code does compile (with warning messages that should not be ignored). The error is a linker error. See below for the solution to this problem.
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2022-11-23T02:18:47.197+00:00

@Komissarov Maxim

I agree with RLWA32-6355:

1, You should use WinMain instead of winMain.

2, You should use return DefWindowProc(hWnd, msg, wParam, lParam); instead of return wndProc(hWnd, msg, wParam, lParam);

For more details I suggest you could refer to the Docs:

Module 1. Your First Windows Program

WinMain function

DefWindowProcA function
Sawyer261 1 Reputation point

2022-11-23T03:10:21.047+00:00

As the coding of WINAPI. Visual Studio was showing the same issue to for Best electric bike app. Then I fully converted the coding to the html and custom coding through simple using the notepad ++ and carefully checked each and every loop of the code. Which is now working fine for all the platforms. So kindly check their will be a loop which will be stopping it.
Komissarov Maxim 41 Reputation points

2022-11-24T17:15:00.033+00:00

Thank you! This helped a lot
RLWA32 49,636 Reputation points

2022-11-24T17:32:30.617+00:00

You may also find it helpful to create a New Project with Visual Studio's template for a Windows Desktop Application. It will create a fully formed project including a menu and resources. Its also a good starting point for learning.

Answer 1

RLWA32 49,636

The function name should be WinMain, not winMain.

The window procedure (wndProc) should call DefWindowProc when handling the default case in the switch statement. Also, the function as written fails to return a value after handling WM_CREATE and WM_DESTROY.

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winMain error C++

include "windows.h"

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