在初始化变量列表中的赋值顺序是否未定义？ [英] Is the order of assignment in a list of initialized variables undefined?

问题描述

可能重复：

如果我有以下代码，逗号是作为正常的序列点，还是行为未定义？

  int i = 1，j = i; 
  

我实际上不打算使用这个（我们的内部标准禁止甚至<$ c

解决方案 / div>

它的定义很好：

8。声明：[dcl.decl]

3）声明中的每个init声明都是单独分析的，

注意：

90）带有几个声明符的声明通常相当于
对应的声明序列，每个声明都有一个
声明符。这是

T D1，D2，... Dn;

通常等价于

T D1; T D2; ... T Dn;

其中T是一个decl-specifier-seq，每个Di都是一个
init声明符。

完整性（因为注释通常 表示）：

当一个名字由
引入的名称隐藏了dcl-specifiers使用的类型名时，就会发生异常，所以当同一个
dcl-说明符在后续声明中使用，它们没有
与在 struct S {...}中相同的含义; S S，T; //声明两个
结构S 的实例，它不等同于 struct S {...}; S
S; S T; // error`

Possible Duplicate:
Is the comma in a variable list a sequence point?

If I have the following code does the comma act as a normal sequence point, or is the behaviour undefined?

int i = 1, j = i;

I don't actually plan to use this (our internal standard prohibits even int i, j) but I was curious and it prooved oddly tricky to google.

解决方案

It's well-defined:

8. Declarators: [dcl.decl]

3) Each init-declarator in a declaration is analyzed separately as if it was in a declaration by itself.

And the note:

90) A declaration with several declarators is usually equivalent to the corresponding sequence of declarations each with a single declarator. That is

T D1, D2, ... Dn;

is usually equvalent to

T D1; T D2; ... T Dn;

where T is a decl-specifier-seq and each Di is an init-declarator.

For completness (because the note says usually):

The exception occurs when a name introduced by one of the declarators hides a type name used by the dcl-specifiers, so that when the same dcl-specifiers are used in a subsequent declaration, they do not have the same meaning, as in struct S { ... }; S S, T; // declare two instances of struct Swhich is not equivalent tostruct S { ... }; S S; S T; // error`

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