#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <tchar.h>
int __cdecl WinMainCRTStartup(void)
{
TCHAR szTmp[MAX_PATH];
int nLen = GetModuleFileName(NULL, szTmp, MAX_PATH);
MessageBox(0, szTmp, 0, MB_OK);
lstrcpy(&szTmp[nLen-3], TEXT("txt"));
MessageBox(0, szTmp, 0, MB_OK);
ExitProcess(0);
}
EDIT: UNICODE fix