Double colon (::) in C is used for: 1. Global namespace access; 2. Namespace qualification; 3. Enum constant access; 4. Static method call; 5. Base class reference.
Double colon (::) in C
In C, double colon (::) operation The symbol has the following uses:
1. Global namespace access
- Used when accessing global variables or functions not declared in the current namespace.
-
For example:
::x = 10; // 访问全局变量 x
2. Namespace qualification
- Specify the variable or function to which Namespaces.
-
For example:
namespace std { int a; } int main() { std::a = 10; // 访问 std 命名空间中的变量 a }
3. Enumeration constant access
- Access in enumeration type used when using constants.
-
For example:
enum Color { Red, Green, Blue }; int main() { Color color = ::Color::Red; // 访问枚举常量 Red }
4. Static method call
- Used when calling static class methods .
-
For example:
class MyClass { public: static void print() { cout << "Hello!" << endl; } }; int main() { MyClass::print(); // 调用静态方法 print }
5. Base class reference
- Reference the base in the derived class Used when class.
-
For example:
class Base { public: void print() { cout << "Base class" << endl; } }; class Derived : public Base { public: void print() { ::Base::print(); // 引用基类方法 print } };
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