事实上，应该工作。请参见 http://gcc.gnu.org/onlinedocs/cpp/If.html#如果

Indeed that should work. See http://gcc.gnu.org/onlinedocs/cpp/If.html#If

这是参考可能是准确的，但写成标准格式 - 抽象而不例子。我很高兴，我发现这个简单的问题和响应，当我有同样的问题。

That reference is probably accurate, but written in "standards format" -- abstractly without examples. I'm glad I found this simple question and response when I had the same issue.