Use of colons (:) and Double colons (::) in C + +

1. Colon (:) usage

(1) Represents the definition of a bit field within a mechanism (that is, the variable occupies several bit spaces)

typedef struct _xxx{

unsigned char a:4;

unsigned char c;

} ; Xxx

(2) The colon at the back of the constructor functions as a method of assigning a value to a member variable, initializing the list, and more appropriate for the const type of the member variable.

struct _xxx{

_xxx (): Y (0xc0) {}

};

(3) Public: and private: The following colon, which indicates that all the members defined later are publicly or privately held until the next "common:" or "Private:" appears. "Private:" is handled by default.

(4) The class name followed by a colon is used to define the inheritance of the class.

Class derived class Name: Inheritance mode base class name

{

Members of derived classes

};

Inheritance mode: Public, private, and protected, default processing is public.

2. Double colon (::) usage

(1) indicates "domain Operator"
Example: Declares a Class A, Class A declares a member function void F (), but does not give the definition of F in the declaration of the class, so when F is defined outside the class,
will be written as void A::f (), which indicates that the F () function is a member function of class A.

(2) Directly before the global function, which means the global function
Example: In the VC, you can call the API function, in front of the API functions:

(3) Representing reference member functions and variables, scope member operators

Example: System::math::sqrt () equivalent to SYSTEM.MATH.SQRT ()
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VC in the following

:: Is the scope decomposition operator in C + +. For example, a Class A is declared, a member function VOIDF () is declared in Class A, but no definition of f is given in the declaration of the class, so the definition of F outside the class is written as Voida::f (), which means that the F () function is a member function of Class A.
:: In general, there is a usage that is directly before the global function, which represents the global function. When the member function of a class has the same name as a global function outside the class, when the test is defined in the class, the name of the function is called by default, and if you want to invoke a global function with the same name, you must hit:: To show the difference. For example, in the VC, you can call the API function, in front of the API functions to add:.

Reprinted from: http://fengqing888.blog.163.com/blog/static/3301141620100623933512/

Use of colons (:) and Double colons (::) in C + +