c++入门学习篇（1）之：：作用域符解析
在C ++中，作用域运算符为::。它用于以下目的。1）当存在具有相同名称的局部变量时，要访问全局变量：
// C++ program to show that we can access a global variable
// using scope resolution operator :: when there is a local
// variable with same name
#include<iostream>
using namespace std;
int x;// Global x
int main()
{
int x = 10; // Local x
cout << "Value of global x is " << ::x;
cout << "\nValue of local x is " << x;
return 0;
} 输出：
全局x的值为0
本地x的值为102）在类之外定义函数。
// C++ program to show that scope resolution operator :: is used
// to define a function outside a class
#include<iostream>
using namespace std;
class A
{
public:
// Only declaration
void fun();
};
// Definition outside class using ::
void A::fun()
{
cout << "fun() called";
}
int main()
{
A a;
a.fun();
return 0;
} 输出：
fun() called3）访问一个类的静态变量。
// C++ program to show that :: can be used to access static
// members when there is a local variable with same name
#include<iostream>
using namespace std;
class Test
{
static int x;
public:
static int y;
// Local parameter 'a' hides class member
// 'a', but we can access it using ::
void func(int x)
{
// We can access class's static variable
// even if there is a local variable
cout << "Value of static x is " << Test::x;
cout << "\nValue of local x is " << x;
}
};
// In C++, static members must be explicitly defined
// like this
int Test::x = 1;
int Test::y = 2;
int main()
{
Test obj;
int x = 3 ;
obj.func(x);
cout << "\nTest::y = " << Test::y;
return 0;
} 输出：
静态x的值为1
本地x的值为3
测试:: y = 24）如果有多个继承：
如果两个祖先类中存在相同的变量名，则可以使用作用域运算符进行区分。
// Use of scope resolution operator in multiple inheritance.
#include<iostream>
using namespace std;
class A
{
protected:
int x;
public:
A() { x = 10; }
};
class B
{
protected:
int x;
public:
B() { x = 20; }
};
class C: public A, public B
{
public:
void fun()
{
cout << "A's x is " << A::x;
cout << "\nB's x is " << B::x;
}
};
int main()
{
C c;
c.fun();
return 0;
}输出：
A的x是10
B的x是205）对于命名空间
如果两个命名空间中都存在一个具有相同名称的类，则可以将名称空间名称与作用域解析运算符一起使用，以引用该类而不会发生任何冲突
// Use of scope resolution operator for namespace.
#include<iostream>
int main(){
std::cout << "Hello" << std::endl;
} 在这里，cout和endl属于std命名空间。
6）在另一个类中引用一个类：
如果另一个类中存在一个类，我们可以使用嵌套类使用作用域运算符来引用嵌套的类
// Use of scope resolution class inside another class.
#include<iostream>
using namespace std;
class outside
{
public:
int x;
class inside
{
public:
int x;
static int y;
int foo();
};
};
int outside::inside::y = 5;
int main(){
outside A;
outside::inside B;
} 笔芯 你是优秀的 [爱]
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