这不是在许多方面的安全。首先，如果任何变量称为T已经存在，它不会编译。

It is not safe in many ways. First, if any variable called t already existed, it wouldn't compile.

除此之外，你必须要小心这样的话：

Apart from that, you have to be careful with things like:

if (...)
    swap(a,b);

如将它扩展为：

if (...)
    int t;
    do { ... } while(0);

注意，因为如果没有括号的，如果块主体将只是一个声明。

Note that the if body would be only a declaration because there are no braces for the if block.

你为什么不声明T内的做阻止？

Why don't you declare t inside the do block?