CODEWITHSUNDEEP
c++grammar
JavaMan
JavaMan

Reputation: 5054

Why Standard C++ Defines Decl-Specifier-Seq Optional

Why in the standard c++ grammar, the decl-specifier-seq under simple-declaration is optional? 

simple-declaration:
 decl-specifier-seq(optional)  init-declarator-list(optional);

According to the spec, only the constructor, destructor and type conversion functions could have no decl-specifier-seq (section 9.2 or section 7 dcl.dcl). But all these 3 function declarations are members of a class, so they should be defined by another grammar rule separated from simple-declaration:

member-declaration:
 decl-specifier-seq(optional) member-declarator-list(optional);
 function-definition ;(optional)
 ::(optional) nested-name-specifier template(optional) unqualified-id ;
 using-declaration
 static_assert-declaration
 template-declaration

Here the decl-specifier-seq is optional as expected. But why in a simple-declaration, it is optional, too?

Upvotes: 7

Views: 399

Answers (1)

aarcangeli
aarcangeli

Reputation: 331

In C++ you can declare a constructor outside of the class scope.

class A {
    A();
};

A::A() {}

Upvotes: 0

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