编译器如何评估数学表达式？

Question

I was reading this question and then I made the following.

a = b + (c - (b = c)) + (a - (c = a))

I tried that in C and Java. It works with java , but not C.

Of course, it depends on how the compiler evaluate such expressions and after googling about that, I failed to find the answer.

Answer 1

The reason why it doesn't work in C is because C doesn't specify exactly when the c = a will occur. It can occur before or after the two other times it is referenced in that statement.

So depending on when the compiler decides to perform the assignment c = a , the value of the expression will vary. It's not defined.

ie If b = c is evaluated before c = a then, b will take the original value of c . If it is evaluated after, then it will take the value of a .

Answer 2

您可以参考java 表达式文档以获得完美答案。