这是完全有效和明智的标准C ++。

This is perfectly valid and sensible standard C++.

三元条件运算符形成一个 expression ，该表达式是一个

The ternary conditional operator forms an expression, and the expression is a constant expression if its operands are.

标准引用为C ++ 11 5.19 / 2：

The standard reference is C++11 5.19/2:

条件表达式是核心常量表达式 [...]

请注意，从5.16开始，三元条件表达式是 conditional-expressions 的一种。其他类型例如 2 == 3 。

Note that by 5.16, ternary conditional expressions are one type of conditional-expressions. Other types are things like 2 == 3.