Undefined reference to WinMain (C++ Mingw)

This example code uses wWinMain but

One thing to note is that Visual C++ supports a “wWinMain” entry point where the “lpCmdLine” parameter is a “LPWSTR”. You would typically use the “_tWinMain” preprocessor definition for your entry point and declare “LPTSTR lpCmdLine” so that you can easily support both ANSI and Unicode builds. However, the MinGW CRT startup library does not support wWinMain, so you’ll have to stick with the standard “WinMain” and use “GetCommandLine()” if you need to access command line arguments.

via Building Win32 GUI Applications with MinGW

In this specific case, you can use WinMain instead. This program doesn't use pCmdLine value, so it should compile when you change wWinMain to WinMain and PWSTR pCmdLine to PSTR pCmdLine.

If you later would need unicode command line use LPWSTR cmd_line = GetCommandLineW(); instead of WinMain argument.

Newer Mingw versions also support -municode linker option switching to alternate startup code allowing to use wWinMain instead of WinMain (or wmain instead of main). Add it to your command line, linker options in IDE or makefile.

g++ other_options_and_arguments -municode

undefined reference to `WinMain'

It tries to find WinMain and failed. So you need use WinMain instead of wWinMain.

Another possible issue is

error: conflicting declaration of C function 'int WinMain(HINSTANCE, HINSTANCE, PWSTR, int)' int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow) ^~~~~~~ In file included from c:\mingw\include\windows.h:44:0, from test.cpp:5: c:\mingw\include\winbase.h:1263:14: note: previous declaration 'int WinMain(HINSTANCE, HINSTANCE, LPSTR, int)' int APIENTRY WinMain (HINSTANCE, HINSTANCE, LPSTR, int);

So you need use LPSTR instead of PWSTR.

Then the entry point will like this:

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, LPSTR pCmdLine, int nCmdShow)

Above is ANSI version entry point.

The solution is to add -municode to the compilation parameters, as mentioned by @ssbssa in a comment. (In the meantime, the accepted answer has been updated, and confirms this).

Example:

g++ helloworld3.cpp -o helloworld3 -Wl,-subsystem,windows -municode

See https://sourceforge.net/p/mingw-w64/wiki2/Unicode%20apps/

While it is not necessary to define _UNICODE or UNICODE to compile the above code, -municode is needed for linking because it uses wmain() instead of the traditional main().