Thanks Vortex!
I missed that.
Unicode support:
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#ifdef UNICODE
int WINAPI MessageBoxTimeoutW(HWND hWnd,LPCWSTR lpText, LPCWSTR lpCaption,
UINT uType, WORD wLanguageId, DWORD dwMilliseconds);
#define MessageBoxTimeout MessageBoxTimeoutW
#else
int WINAPI MessageBoxTimeoutA(HWND hWnd,LPCSTR lpText, LPCSTR lpCaption,
UINT uType, WORD wLanguageId, DWORD dwMilliseconds);
#define MessageBoxTimeout MessageBoxTimeoutA
#endif
#define TIMEOUT_VALUE 5000
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,LPSTR lpCmdLine, int nCmdShow)
{
MessageBoxTimeout(0,TEXT("MessageBoxTimeout demo\nTimeout value = 5000 ms"),TEXT("Hello!"),MB_OK,LANG_NEUTRAL,TIMEOUT_VALUE);
return 0;
}