Is long long a type in C?

问题:

I know the title seems quite stupid, but I think it's worth asking.

Take this declaration(or definition, maybe) for example:

_Thread_local long volatile static int _Atomic const long unsigned x = 10;

I used to consider long long as a type, but if it's a type name, how can so many qualifiers be inserted into it?

So I consulted N1570 with this question, only to be more confused. It mentions some terms such as "type-specifier" and "type-qualifier", and I can't find long long in "type specifiers", but isn't long long a primitive type in C? There are so many books telling me so!

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Clarifying not duplicate:

Yes, I saw an existing question deals with long int long, but this question have something to do with qualifiers, and is in C.

回答1:

If you read the right bits of the standard carefully enough, you find that the monster declaration in the question is valid, even if implausible.

The 'right bits' includes:

6.2.5 Types

There are five standard signed integer types, designated as signed char, short int, int, long int, and long long int. (These and other types may be designated in several additional ways, as described in 6.7.2.)

…

For each of the signed integer types, there is a corresponding (but different) unsigned integer type (designated with the keyword unsigned) that uses the same amount of storage (including sign information) and has the same alignment requirements.

6.7.2 Type specifiers

At least one type specifier shall be given in the declaration specifiers in each declaration, and in the specifier-qualifier list in each struct declaration and type name. Each list of type specifiers shall be one of the following multisets (delimited by commas, when there is more than one multiset per item); the type specifiers may occur in any order, possibly intermixed with the other declaration specifiers.

…

• long long, signed long long, long long int, or signed long long int
• unsigned long long, or unsigned long long int

Other declaration specifiers include storage classes (static and _Thread_local in the example), and type qualifiers (volatile and _Atomic).

6.7 Declarations

6.7 Declarations

Syntax

declaration:
     declaration-specifiers init-declarator-listopt ;
     static_assert-declaration

declaration-specifiers:
     storage-class-specifier
     declaration-specifiers_opt
     type-specifier declaration-specifiers_opt
     type-qualifier declaration-specifiers_opt
     function-specifier declaration-specifiers_opt
     alignment-specifier declaration-specifiers_opt

Also, as noted by Olaf in a comment:

6.11.5 Storage-class specifiers

The placement of a storage-class specifier other than at the beginning of the declaration specifiers in a declaration is an obsolescent feature.

It is also eccentric to split up the integer type keywords (the type specifier). A more orthodox version of the declaration would be:

static _Thread_local _Atomic const volatile unsigned long long int x = 10;

(or it might drop the int).