def find_available_vc_vers(self):
        """
        Find all available Microsoft Visual C++ versions.
        """
        ms = self.ri.microsoft
        vckeys = (self.ri.vc, self.ri.vc_for_python, self.ri.vs)
        vc_vers = []
        for hkey in self.ri.HKEYS:
            for key in vckeys:
                try:
                    bkey = winreg.OpenKey(hkey, ms(key), 0, winreg.KEY_READ)
                except (OSError, IOError):
                    continue
                subkeys, values, _ = winreg.QueryInfoKey(bkey)
                for i in range(values):
                    try:
                        ver = float(winreg.EnumValue(bkey, i)[0])
                        if ver not in vc_vers:
                            vc_vers.append(ver)
                    except ValueError:
                        pass
                for i in range(subkeys):
                    try:
                        ver = float(winreg.EnumKey(bkey, i))
                        if ver not in vc_vers:
                            vc_vers.append(ver)
                    except ValueError:
                        pass
        return sorted(vc_vers)
Find all available Microsoft Visual C++ versions.