差异I = I + + + +的C输出;且i = ++ I + C ++; [英] Difference in output of i=i++ + ++c; and i=++i + c++;

问题描述

我不知道这是编译器特定的，但是当我试图运行两位前pressions DEVC ++

I don't know if this is compiler specific but when I tried running the two expressions in DevC++

在 I = C = B = 0; I = I + + + +ç给 2 ，而 I = + I + C ++ 给 1

不过，
     B = I + + + +ç和
     B = + I + + +ç产生的结果 1 这两个前pressions。

But b=i++ + ++c and b=++i + ++c produces the result 1 for both expressions.

我不知道，在一个未定义的值在相同的前pression结果递增一个变量两次根据 C 标准规范，但我很好奇如何编译器生成这些输出。可能有人请解释如何，为什么？

I do know that incrementing a variable twice in the same expression results in an undefined value according to the C standard specification but I'm curious how the compiler produces these output. Could someone please explain how and why?

推荐答案

我++ 和 ++我完全不同，我++ 是后递增，这意味着评估 I 在EX pression然后递增一次的评估。 ++我表示则增量评估前pression。
我在你的例子中看到您设置 I = ++ I / I ++ ，这是因为在评论中提及未定义的行为。

i++ and ++i are completely different, i++ is post increment which means evaluate i in the expression and then increment once its evaluated. ++i means increment then evaluate the expression. I see in your example you set i = ++i/i++, this is undefined behavior as mentioned in a comment.

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