c - C 形式定义中的命名空间

Question

我正在阅读 N1570标准并且在理解 namespace 定义的措辞方面有问题。这是它:

1 If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate name spaces for various categories of identifiers, as follows:

— label names (disambiguated by the syntax of the label declaration and use);

— the tags of structures, unions, and enumerations (disambiguated by following any³²⁾ of the keywords struct, union, or enum);

— the members of structures or unions; each structure or union has a separate name space for its members (disambiguated by the type of the expression used to access the member via the . or -> operator);

— all other identifiers, called ordinary identifiers (declared in ordinary declarators or as enumeration constants).

³²⁾ There is only one name space for tags even though three are possible.

他们在这里谈论的是在超过 1 个特定标识符声明可见的情况下。现在，类似“要访问标识符，应指定其命名空间”或“要访问特定命名空间中的标识符...”之类的话。

Answer 1

让我先举个例子(这是严格为了理解的目的，不要写这样的代码，永远)

#include  <stdio.h>


int main(void)
{
    int here = 0;    //.......................ordinary identifier
    struct here {    //.......................structure tag
        int here;    //.......................member of a structure
    } there;

here:                             //......... a label name
     here++;
     printf("Inside here\n");
     there.here = here;           //...........no conflict, both are in separate namespace
     if (here > 2) {
         return 0; 
     }
     else
       goto here;                 //......... a label name

    printf("Hello, world!\n");          // control does not reach here..intentionally :)
    return 0;
}

您可以在此处看到标识符的用法。根据规则，它们属于不同的命名空间，因此这个程序没问题。

但是，例如，您将结构变量名称从 there 更改为 here，您会看到冲突，因为那时会有同一命名空间中同一标识符(普通标识符)的两个单独声明。