What is the difference between "::" "." and "->" in c++ [duplicate]

Question

I created a class called Kwadrat. The class has three int fields. My Development Environment suggests that I access the fields from Kwadrat created objects via the :: & -> operators. I tried both operators, and found that the -> operator is able to successfully access the data in the objects fields, although, the same cannot be said for the -> operator. I have also found that the . operator will access class members as well. I am confused, and don't understand why there are three members for accessing object members &/or methods. Can someone please explain to me what the difference is between the three operators?

---

          1. ->

          2. ::

          3. .

---

      #include <iostream>      using namespace std;      class Kwadrat{      public:          int val1,             val2,             val3;          Kwadrat(int val1, int val2, int val3)         {             this->val1 = val1; // Working             this.val2 = val2;  // Doesn't Work!             this::val3 = val3; // Doesn't Work!         }     };       int main()     {         Kwadrat* kwadrat = new Kwadrat(1,2,3);          cout<<kwadrat->val1<<endl;         cout<<kwadrat->val2<<endl;         cout<<kwadrat->val3<<endl;          return 0;     }   

Answer 1

1.-> for accessing object member variables and methods via pointer to object

Foo *foo = new Foo(); foo->member_var = 10; foo->member_func(); 

2.. for accessing object member variables and methods via object instance

Foo foo; foo.member_var = 10; foo.member_func(); 

3.:: for accessing static variables and methods of a class/struct or namespace. It can also be used to access variables and functions from another scope (actually class, struct, namespace are scopes in that case)

int some_val = Foo::static_var; Foo::static_method(); int max_int = std::numeric_limits<int>::max(); 

Answer 2

In C++ you can access fields or methods, using different operators, depending on it's type:

• ClassName::FieldName : class public static field and methods
• ClassInstance.FieldName : accessing a public field (or method) through class reference
• ClassPointer->FieldName : accessing a public field (or method) dereferencing a class pointer

Note that :: should be used with a class name rather than a class instance, since static fields or methods are common to all instances of a class.

class AClass{ public: static int static_field; int instance_field;  static void static_method(); void method(); }; 

then you access this way:

AClass instance; AClass *pointer = new AClass();  instance.instance_field; //access instance_field through a reference to AClass instance.method();  pointer->instance_field; //access instance_field through a pointer to AClass pointer->method();  AClass::static_field;   AClass::static_method();