Does typedef of a structure without tag creates distinct type each time it is used and if not why?

Question

I'm wondering if you declare a structure like this:

typedef struct 
{
    //...
} name;

Then is it the case that every subsequent declaration of type 'name' will have distinct type?

I'm wondering this because of (from standard) $6.7.2.3(p5):

Two declarations of structure, union, or enumerated types which are in different scopes or use different tags declare distinct types. Each declaration of a structure, union, or enumerated type which does not include a tag declares a distinct type.

And this $6.7.8(p3):

In a declaration whose storage-class specifier is typedef, each declarator defines an identifier to be a typedef name that denotes the type specified for the identifier in the way described in 6.7.6.

And so something like this would be illegal (although clang will accept it):

typedef struct{
    int a, b;
} s;

void func(s);

int main()
{
   s a = {2, 2};
   s b = a;
}

If it is not the case please explain why?

Answer 1

Each declaration of a structure, union, or enumerated type which does not include a tag declares a distinct type.

这一行是说每次你声明这样一个 type，那都是一个新类型。这并不是说每次你声明一个这样类型的变量时，你就声明了一个新类型。

您的代码只声明一次类型，因此它只创建一种类型。

Answer 2

我想你误会了

结构、联合或枚举类型的每个声明

这是一个结构类型的声明：

struct s1 {
    int a, b;
};

这也是

typedef struct {
    int a, b;
} s2;

它也是 typedef 的声明。这是结构类型和对象的声明：

struct {
    int a, b;
} o1;

这不是结构类型的声明：

s2 o4, o5;

它是两个对象的声明，每个对象都有结构类型。但是这里没有声明结构类型。

该标准特别指出

struct-or-union-speci?er 中存在的struct-declaration-list声明了翻译单元内的新类型。

这种结构声明列表是括号内的一切。

所以这也不是结构类型的声明：

struct s1 o2, o3;

同样，它声明对象，并为它们提供结构类型，但由于缺少struct-declaration-list，它不声明类型。