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I accidentally happened to find this in one of the source codes I was looking at. So, I'm giving a similar smaller example here.
In the file test.h:
#include<iostream>
class test{
int i;
public:
test(){}
//More functions here
};
In the file test.cpp:
#include "test.h"
int main()
{
test test1;
test::test test2;
test::test::test test3;
return 0;
}
First of all, is there a reason to declare test2 that way? Secondly, this code compiles just fine in g++ version 4.4.3 and lower versions. Is there something in the C++ standard, saying, scope resolution operators are ignored when there is no need to resolve scope?
980
The scope resolution operator ( :: ) is used for several reasons. For example: If the global variable name is same as local variable name, the scope resolution operator will be used to call the global variable. It is also used to define a function outside the class and used to access the static variables of class.
In C++, scope resolution operator is ::. It is used for following purposes. 2) To define a function outside a class. 3) To access a class's static variables.
Which of the following is the scope resolution operator? a) . Explanation: :: operator is called scope resolution operator used for accessing a global variable from a function which is having the same name as the variable declared in the function.
C++ supports the scope resolution operator (::) that allows us to resolve the ambiguous call or reference to identifiers. Like C++, Java does not support the scope resolution operator. Java uses the same operator (::) but with different names.
This code is not valid.
It was a bug in g++ that it accepted the code. See "g++ does not treat injected class name correctly." The bug was resolved as fixed in 2009, so it should be fixed in any recent version of g++.
131
To clarify the situation, as specified in §9/2:
A class-name is inserted into the scope in which it is declared immediately after the class-name is seen. The class-name is also inserted into the scope of the class itself; this is known as the injected-class-name. For purposes of access checking, the injected-class-name is treated as if it were a public member name.
However, as specified in §3.4.3.1/1:
If the nested-name-specifier of a qualified-id nominates a class, the name specified after the nested-namespecifier is looked up in the scope of the class (10.2), except for the cases listed below.
[ ... §3.4.3.1/2]:
In a lookup in which the constructor is an acceptable lookup result and the nested-name-specifier nominates a class C:
— if the name specified after the nested-name-specifier, when looked up in C, is the injected-class-name of C (Clause 9) [ ... ] the name is instead considered to name the constructor of class C.
[ ... example: ]
struct A { A(); };
[ ... ]
A::A a; // error, A::A is not a type name
struct A::A a2; // object of type A
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