C++ 声明顺序(在多变量声明行中)

Question

我在我的 C++ 代码中使用以下内容:

int a = 0, b = a;

我想知道这种行为是否可靠且定义明确(名称声明从左到右的顺序)，并且我的代码不会因未声明的名称错误而与其他编译器中断。

如果不可靠，我会打破声明:

int a = 0; 
int b = a;

谢谢。

Answer 1

我认为答案是否定的。

受制于core active issue 1342其中说:

It is not clear what, if anything, in the existing specification requires that the initialization of multiple init-declarators within a single declaration be performed in declaration order.

我们在[dcl.decl]p3中有不规范的说明其中说:

...[ Note: 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 equivalent to

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

...

但它是非规范的，它根本不涵盖初始化情况，据我所知，没有规范的措辞说同样的话。

尽管该标准确实涵盖了 [basic.scope.pdecl]p1 中的名称范围其中说:

The point of declaration for a name is immediately after its complete declarator and before its initializer (if any), except as noted below. [ Example:

unsigned char x = 12;
{ unsigned char x = x; }

Here the second x is initialized with its own (indeterminate) value. — end example  ]