为什么sizeof的视为运营商？ [英] Why is sizeof considered as an operator?

问题描述

为什么的sizeof 认为作为一个经营者，而不是一个功能？

Why is sizeof considered as an operator and not a function ?

什么财产是必要的资格作为操作？

What property is necessary to qualify as an operator ?

推荐答案

由于C标准是这样说的，而且它得到了投票。

Because the C standard says so, and it gets the only vote.

至于后果：

• 的sizeof的操作数可以是裸投，的sizeof（INT），而不是一个对象前pression。


• 括号是不必要的： int类型的;的printf（％d个\\ n，sizeof的一个）; 是完全没有问题。他们经常看到的，首先因为他们需要一个类型转换前pression的一部分，其次是因为sizeof的具有非常高的precedence，所以 sizeof的A + B 是不一样的的sizeof（A + b）。但他们不是的sizeof调用的一部分，它们是操作的一部分。


• 您不能把sizeof的地址。


• 这位前pression这是sizeof运算的操作数是不是在运行时进行评估（的sizeof一个++ 不修改）。


• 这位前pression这是sizeof运算的操作数可以是任意类型，除了无效或函数类型。事实上，这是种的sizeof点的。

• The operand of sizeof can be a bare cast, sizeof (int), instead of an object expression.
• The parentheses are unnecessary: int a; printf("%d\n", sizeof a); is perfectly fine. They're often seen, firstly because they're needed as part of a type cast expression, and secondly because sizeof has very high precedence, so sizeof a + b isn't the same as sizeof (a+b). But they aren't part of the invocation of sizeof, they're part of the operand.
• You can't take the address of sizeof.
• The expression which is the operand of sizeof is not evaluated at runtime (sizeof a++ does not modify a).
• The expression which is the operand of sizeof can have any type except void, or function types. Indeed, that's kind of the point of sizeof.

一个函数将在所有这些点不同。可能有一个函数和一个一元运算符之间的其他差异，但我认为这足以说明为什么sizeof的不可能是一个函数即使是希望它是有原因的。

A function would differ on all those points. There are probably other differences between a function and a unary operator, but I think that's enough to show why sizeof could not be a function even if there was a reason to want it to be.

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