是a = 0; b =（a ++，a + 1）;未定义行为（UB）？ [英] Is a = 0; b = (a++, a + 1) ; undefined behavior (UB)?

问题描述

查看简单示例：

int a = 0;
int b = (a ++  ,  a + 1); // result of b is UB or well defined ?  (c++03).

在c ++ 11 / c ++ 14中更改了

This was changed in c++11/c++14 ?

推荐答案

结果是很好定义的，自从C ++ 98。逗号运算符在 a 的写入和第二次读取之间引入序列点（或在后面的C ++中的先后顺序关系），而我不请参阅任何其他未定义行为的潜在原因。

The result is well defined and has been since C++98. The comma operator introduces a sequence point (or a "sequenced before" relationship in later C++s) between the the write and the second read of a and I don't see any other potential reasons for undefined behavior.

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