这些分配之间是否有顺序点? [英] Is there a sequence point between these assignments?

问题描述

以下代码中的两个赋值之间是否有一个序列点:

Is there a sequence point between the two assignments in the following code:

f(f(x=1,1),x=2);

推荐答案

来自

The relevant quote from the (draft) standard [6.5.2.2, 10] is:

功能指示符的求值顺序， 实际的参数和 实际参数未指定，但是有一个序列 在实际通话之前指向.

The order of evaluation of the function designator, the actual arguments, and subexpressions within the actual arguments is unspecified, but there is a sequence point before the actual call.

因此对于您的表达式，第一个参数(尤其是对f的调用)可能是 在第二个参数之前求值；例如:

So for your expression, the first argument (in particular the call to f) could be evaluated before the second argument; e.g.:

(x = 1, 1), f <sp> call, (x = 2), f <sp> call

或者，它可以在第二个参数之后求值；例如:

Or, it could be evaluated after the second argument; e.g.:

(x = 2), (x = 1, 1), f <sp> call, f <sp> call

[函数调用本身可以(而且很可能会)包含更多的序列点(特别是如果包含return语句的话).]

[The function call itself can (and most probably will) contain more sequence points (in particular if it contains a return statement).]

据此，分配之间是否存在一个序列点. 这取决于平台(未指定").

Depending on that, there is a sequence point between the assignments or not. It is up to the platform ("unspecified").

由于在第二种情况下，您要在两个序列点之间两次分配给x，所以您在这种平台上有未定义的行为.

Since in the 2nd case, you are assigning to x twice between two sequence points, you have undefined behaviour on such a platform.

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