The difference between :: and . in c++

The colon (::) is used to access the global namespace or static members of the class, while the period (.) is used to access the instance members of the class. For example, std::cout uses :: to access functions in the global namespace, and obj.instanceVar uses . to access instance member variables of a class.

The difference between:: and .

Short answer:

Colon (::) is used to access the global namespace or static members of the class, while period (.) is used to access instance members of the class.

Detailed answer:

Colon (::)

• is used to access objects defined in the global namespace Identifier, variable, or function, for example: std::cout.
• Used to access static members of a class (that is, members that do not depend on object instances), for example: ClassName::staticMember.
• is used to qualify the class name to avoid name conflicts, for example: namespaceA::ClassName.

Period (.)

• is used to access instance members of a class (that is, members associated with specific object instances), for example: object.instanceMember.
• Used to call member functions of a class, for example: object.memberFunction().
• is used to access the member pointed to by the object pointer or reference, for example: *objectPtr.member.

Example:

<code class="cpp">// 全局命名空间的函数
std::cout << "Hello world!" << std::endl;

// 类的静态成员变量
class MyClass {
public:
    static int staticVar;
};
int MyClass::staticVar = 42;

// 类的实例成员变量和函数
class MyObject {
public:
    int instanceVar;
    void instanceFunc() {
        std::cout << instanceVar << std::endl;
    }
};
MyObject obj;
obj.instanceVar = 10;
obj.instanceFunc(); // 输出: 10</code>

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