C++ 作用域解析运算符

本节将讨论作用域解析运算符及其在C++编程语言中的各种用途。作用域解析运算符用于引用超出作用域的全局变量或成员函数。因此，我们使用作用域解析运算符来访问程序中隐藏的变量或函数。该运算符表示为双冒号(::)符号。

示例，在程序中，当全局变量或局部变量或函数具有相同的名称时，当我们调用变量时，默认情况下只访问内部或局部变量，而不是调用全局变量。通过这种方式，它隐藏了全局变量或函数。为了克服这种情况，我们使用作用域解析运算符来获取程序的隐藏变量或函数。

作用域解析运算符的用途

1. 它用于访问程序的隐藏变量或成员函数。
2. 它使用作用域解析定义类外部的成员函数。
3. 它用于访问类的静态变量和静态函数。
4. 作用域解析运算符用于继承中的函数覆盖。

使用作用域解析(::)运算符访问隐藏值的程序

Program1.cpp

#include 
using namespace std;
// declare global variable
int num = 50;
int main ()
{
// declare local variable 
int num = 100;

// print the value of the variables
cout << " The value of the local variable num: " << num;

// use scope resolution operator (::) to access the global variable 
cout << "\n The value of the global variable num: " << ::num; 
return 0;
}

输出

The value of the local variable num: 100
 The value of the global variable num: 50

使用作用域解析运算符（::）在类外定义成员函数的程序

Program2.cpp

#include 
using namespace std;
class Operate
{
public:
    // declaration of the member function
    void fun();
};
// define the member function outside the class.
void Operate::fun()   /* return_type Class_Name::function_name */
{
cout << " It is the member function of the class. ";
}
int main ()
{
 // create an object of the class Operate
Operate op;
op.fun();
return 0;
}

输出

It is the member function of the class.

使用作用域解析符(::)运算符演示标准命名空间的程序

Program3.cpp

#include 
int main ()
{
int num = 0;

// use scope resolution operator with std namespace
std :: cout << " Enter the value of num: ";
std::cin >> num;
std:: cout << " The value of num is: " << num;
}

输出

Enter the value of num: 50
 The value of num is: 50

使用作用域解析（::）运算符访问静态变量的程序

Program4.cpp

#include 
using namespace std; 
class Parent
{
static int n1;
public:
static int n2;
// The class member can be accessed using the scope resolution operator.
void fun1 ( int n1)
{
// n1 is accessed by the scope resolution operator (:: ) 
cout << " The value of the static integer n1: " << Parent::n1;
cout << " \n The value of the local variable n1: " << n1;
}
};
// define a static member explicitly using :: operator
int Parent::n1 = 5; // declare the value of the variable n1
int Parent::n2 = 10;    
int main ()
{
Parent b;
int n1 = 15;
b.fun1 (n1);
cout << " \n The value of the Base::n2 = " << Parent::n2;
return 0;
}   

输出

The value of the static integer n1: 5
 The value of the local variable n1: 15
 The value of the Base::n2 = 10

使用作用域解析运算符(::)访问静态成员函数的程序

Program5.cpp

#include 
using namespace std;
class ABC
{
public:
// declare static member function
static int fun()
{
cout << " \n Use scope resolution operator to access the static member. ";
}
};
int main () 
{
// class_name :: function name
ABC :: fun ();
return 0;
}

输出

Use scope resolution operator to access the static member.

使用作用域限定符(::)重写成员函数的程序

Program5.cpp

#include 
using namespace std;
class ABC
{
// declare access specifier
public:
void test ()
{
cout << " \n It is the test() function of the ABC class. ";
}
};
// derive the functionality or member function of the base class
class child : public ABC
{
public:
void test()
{
ABC::test();
cout << " \n It is the test() function of the child class. ";
}
};
int main ()
{
// create object of the derived class
child ch;
ch.test();
return 0;
}

输出

 It is the test() function of the ABC class.
 It is the test() function of the child class.