C ++ 17后增量操作 [英] C++17 post increment operation

问题描述

C ++ 17

有人可以解释

int number{5};
number = (number++) + 10;

给出15条输出，

int number {5};
number = (++number) + 10;

给出16的输出？

推荐答案

在采用了P0145 （在C ++ 17中），第一个示例的行为不确定。可能发生任何事情。

Before P0145 was adopted (in C++17), the first example had undefined behaviour. Anything could happen.

在C ++ 11之前，两者都有不确定的行为。

Before C++11, both had undefined behaviour.

在C ++ 17中，都没有不确定的行为。

In C++17, neither has undefined behaviour. That doesn't mean it's code you want to be writing.

如果我们理解后缀和前缀增量之间的区别：

• number ++ ： number 变为6，但表达式的计算结果为5


• 十加到表达式中


• 结果（15）存储在 number
  

• number++: number becomes 6 but the expression evaluates to 5
• ten is added to the expression
• the result (15) is stored in number

• ++ number ： number 变为6且表达式的计算结果为6


• ten被添加到表达式中


• 结果（16）存储在 number

• ++number: number becomes 6 and the expression evaluates to 6
• ten is added to the expression
• the result (16) is stored in number

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