令人困惑的运算符优先级:<< b + c<< d [英] Confusing operator precedence: a << b + c << d

问题描述

运算符+的优先级高于C ++中的<<，这意味着表达式a << b + c << d的求值应为:

Operator + has higher precedence than << in C++, which would mean that expression a << b + c << d should be evaluated as:

a << (b + c) << d

但是没有道理.跟随时可以获得更多的感觉

But that does not make sense. More sense can be obtained when following

a << (b + (c << d))

但这违反了+优于<<的优先级，不是吗?编译器如何评估有意义"部分?

But that violates precedence of the + over <<, doesn't it? How do compilers evaluate the "does makes sense" part?

更新:当问这个问题时，我认为编译器使用了第二个变体，这就是为什么我想知道编译器如何进行此评估.实际上，首先使用的是正确的.

UPDATE: When asking the question I thought that second variant is used by the compiler, which is why I wondering how did the compiler come to this evaluation. In fact, first one is used and it's the correct one.

推荐答案

理解"是主观的.这就是为什么编译器不评估感觉"，而是评估基于一组规则的语法的原因.由于<<具有更高的优先级(由这些规则集提供)，因此将表达式的计算结果为

"Makes sense" is subjective. Which is why compilers don't evaluate "sense", but a grammar based on a set of rules. Becuase << has higher precedence (which is given by those set of rules), it evaluates the expression as

 a << (b + c) << d

如有疑问，请使用括号.

When in doubt, use parenthesis.

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