操作数的计算顺序 [英] order of evaluation of operands

问题描述

在除权pression A + B 是 A 保证被评估之前 b ，或者是评估未指定的顺序？我认为是后者，但我很难找到标准的一个明确的答案。

由于我不知道C是否处理从C ++这种不同的，如果为了评价规则进行了简化在C ++ 11，我会标记了一个问题，所有三个。

解决方案

在C ++中，对于用户自定义类型 A + B 是一个函数调用，标准说

  

    

§5.2.2.8 - [...]函数参数的评估顺序为未指定。 [...]

  

有关运营商正常的标准说：

  

    

第5.4节 - 除非另有说明，个体经营者和个人前pressions的SUBEX pressions，并在其中的副作用发生的顺序，操作数的计算顺序为未指定。 [...]

  

这些都没有改变对C ++ 11。然而，在第二个的措词变化的说，顺序是 unsequenced 的，而不是未指定的，但是它在本质上是一样的。

我没有C标准的副本，但我想，这是同有作为。

In the expression a + b, is a guaranteed to be evaluated before b, or is the order of evaluation unspecified? I think it is the latter, but I struggle to find a definite answer in the standard.

Since I don't know whether C handles this different from C++, or if evaluation order rules were simplified in C++11, I'm gonna tag the question as all three.

解决方案

In C++, for user-defined types a + b is a function call, and the standard says:

§5.2.2.8 - [...] The order of evaluation of function arguments is unspecified. [...]

For normal operators, the standard says:

§5.4 - Except where noted, the order of evaluation of operands of individual operators and subexpressions of individual expressions, and the order in which side effects take place, is unspecified. [...]

These haven't been changed for C++11. However, the wording changes in the second one to say that the order is "unsequenced" rather than unspecified, but it is essentially the same.

I don't have a copy of the C standard, but I imagine that it is the same there as well.

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