C ++标准的哪一部分允许在括号中声明变量？ [英] Which part of the C++ standard allow to declare variable in parenthesis?

问题描述

考虑以下代码：

int main() {
    int(s);
}

我为它创建有效变量 s 。有人可以解释这里发生了什么吗？

I am surprised by the fact that it creates valid variable s. Can anyone explain what's happening here?

推荐答案

[dcl。意义]在标准中说：

[dcl.meaning] in the Standard says:

在声明 TD 中，其中 D 的格式为（D1）包含的 declarator-id 的类型与声明<$ c中包含的 declarator-id 的类型相同$ c> T D1 。

In a declaration T D where D has the form ( D1 ) the type of the contained declarator-id is the same as that of the contained declarator-id in the declaration T D1.

括号不会更改嵌入的 declarator-id 的类型，但可以更改绑定

Parentheses do not alter the type of the embedded declarator-id, but they can alter the binding of complex declarators.

更简单地说，您可以在任何被认为是声明符的地方加上括号。在C ++语法中。 （松散地说，声明符是声明的一部分，没有包含一个名称的初始说明符和类型。）

More simply, you can put parentheses around anything considered a "declarator" in the C++ grammar. (Loosely speaking, a declarator is a part of a declaration without the initial specifiers and types which contains one name.)

在您的示例中，标识符 s 是一个声明符，因此您可以在其周围加上括号，并且含义不会改变。

In your example, the identifier s is a declarator, so you're allowed to put parentheses around it and the meaning doesn't change.

第二个引用的句子暗示了这样做的原因，当事情变得更复杂时，这是必要的。一个例子：

The reason for this, as the second quoted sentence hints, is that it can be necessary when things get more complicated. One example:

int * a [10];     // a is an array of ten pointers to int.
int ( * b ) [10]; // b is a pointer to an array of ten ints.

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