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C#运算符重载

可以重新定义或重载大部分C#提供内置的运算符。因此,程序员可以使用使用用户定义类型运算符也是如此。重载运算符符合特殊名称关键字操作之后的操作符号被定义的功能。像其他功能,重载运算符返回类型和参数列表。

例如,看一下下面的函数:

public static Box operator+ (Box b, Box c)
{
   Box box = new Box();
   box.length = b.length + c.length;
   box.breadth = b.breadth + c.breadth;
   box.height = b.height + c.height;
   return box;
}

上述功能实现了加法运算符(+),用于一个用户定义的类Box。它增加了两个Box对象的属性,并返回得到Box对象。

运算符重载的实现

下面的程序显示了完整的实现:

using System;

namespace OperatorOvlApplication
{
   class Box
   {
      private double length;      // Length of a box
      private double breadth;     // Breadth of a box
      private double height;      // Height of a box

      public double getVolume()
      {
         return length * breadth * height;
      }
      public void setLength( double len )
      {
         length = len;
      }

      public void setBreadth( double bre )
      {
         breadth = bre;
      }

      public void setHeight( double hei )
      {
         height = hei;
      }
      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c)
      {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }

   }

   class Tester
   {
      static void Main(string[] args)
      {
         Box Box1 = new Box();         // Declare Box1 of type Box
         Box Box2 = new Box();         // Declare Box2 of type Box
         Box Box3 = new Box();         // Declare Box3 of type Box
         double volume = 0.0;          // Store the volume of a box here

         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}", volume);

         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);

         // Add two object as follows:
         Box3 = Box1 + Box2;

         // volume of box 3
         volume = Box3.getVolume();
         Console.WriteLine("Volume of Box3 : {0}", volume);
         Console.ReadKey();
      }
   }
}

让我们编译和运行上面的程序,这将产生以下结果:

Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400

重载与非重载操作符

下表描述了运算符在C#重载的能力:

运算符 描述
+, -, !, ~, ++, -- 这些一元运算符需要一个操作数,并可以被重载
+, -, *, /, % 这些二元运算符需要一个操作数,并可以被重载
==, !=, <, >, <=, >= 比较操作符可以被重载
&&, || 条件逻辑运算符不能直接重载
+=, -=, *=, /=, %= 赋值运算符不能被重载
=, ., ?:, ->, new, is, sizeof, typeof 这些运算符不能被重载

例子:

在上面讨论中,让我们扩展前面的例子,并重载几个运算符:

using System;

namespace OperatorOvlApplication
{
    class Box
    {
       private double length;      // Length of a box
       private double breadth;     // Breadth of a box
       private double height;      // Height of a box
      
       public double getVolume()
       {
         return length * breadth * height;
       }
      public void setLength( double len )
      {
          length = len;
      }

      public void setBreadth( double bre )
      {
          breadth = bre;
      }

      public void setHeight( double hei )
      {
          height = hei;
      }
      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c)
      {
          Box box = new Box();
          box.length = b.length + c.length;
          box.breadth = b.breadth + c.breadth;
          box.height = b.height + c.height;
          return box;
      }
      
      public static bool operator == (Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length == rhs.length && lhs.height == rhs.height 
             && lhs.breadth == rhs.breadth)
          {
              status = true;
          }
          return status;
      }
      public static bool operator !=(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length != rhs.length || lhs.height != rhs.height 
              || lhs.breadth != rhs.breadth)
          {
              status = true;
          }
          return status;
      }
      public static bool operator <(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length < rhs.length && lhs.height 
              < rhs.height && lhs.breadth < rhs.breadth)
          {
              status = true;
          }
          return status;
      }

      public static bool operator >(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length > rhs.length && lhs.height 
              > rhs.height && lhs.breadth > rhs.breadth)
          {
              status = true;
          }
          return status;
      }

      public static bool operator <=(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length <= rhs.length && lhs.height 
              <= rhs.height && lhs.breadth <= rhs.breadth)
          {
              status = true;
          }
          return status;
      }

      public static bool operator >=(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length >= rhs.length && lhs.height 
             >= rhs.height && lhs.breadth >= rhs.breadth)
          {
              status = true;
          }
          return status;
      }
      public override string ToString()
      {
          return String.Format("({0}, {1}, {2})", length, breadth, height);
      }
   
   }
    
   class Tester
   {
      static void Main(string[] args)
      {
        Box Box1 = new Box();          // Declare Box1 of type Box
        Box Box2 = new Box();          // Declare Box2 of type Box
        Box Box3 = new Box();          // Declare Box3 of type Box
        Box Box4 = new Box();
        double volume = 0.0;   // Store the volume of a box here

        // box 1 specification
        Box1.setLength(6.0);
        Box1.setBreadth(7.0);
        Box1.setHeight(5.0);

        // box 2 specification
        Box2.setLength(12.0);
        Box2.setBreadth(13.0);
        Box2.setHeight(10.0);

       //displaying the Boxes using the overloaded ToString():
        Console.WriteLine("Box 1: {0}", Box1.ToString());
        Console.WriteLine("Box 2: {0}", Box2.ToString());
        
        // volume of box 1
        volume = Box1.getVolume();
        Console.WriteLine("Volume of Box1 : {0}", volume);

        // volume of box 2
        volume = Box2.getVolume();
        Console.WriteLine("Volume of Box2 : {0}", volume);

        // Add two object as follows:
        Box3 = Box1 + Box2;
        Console.WriteLine("Box 3: {0}", Box3.ToString());
        // volume of box 3
        volume = Box3.getVolume();
        Console.WriteLine("Volume of Box3 : {0}", volume);

        //comparing the boxes
        if (Box1 > Box2)
          Console.WriteLine("Box1 is greater than Box2");
        else
          Console.WriteLine("Box1 is  greater than Box2");
        if (Box1 < Box2)
          Console.WriteLine("Box1 is less than Box2");
        else
          Console.WriteLine("Box1 is not less than Box2");
        if (Box1 >= Box2)
          Console.WriteLine("Box1 is greater or equal to Box2");
        else
          Console.WriteLine("Box1 is not greater or equal to Box2");
        if (Box1 <= Box2)
          Console.WriteLine("Box1 is less or equal to Box2");
        else
          Console.WriteLine("Box1 is not less or equal to Box2");
        if (Box1 != Box2)
          Console.WriteLine("Box1 is not equal to Box2");
        else
          Console.WriteLine("Box1 is not greater or equal to Box2");
        Box4 = Box3;
        if (Box3 == Box4)
          Console.WriteLine("Box3 is equal to Box4");
        else
          Console.WriteLine("Box3 is not equal to Box4");

        Console.ReadKey();
      }
    }
}

让我们编译和运行上面的程序,这将产生以下结果:

Box 1: (6, 7, 5)
Box 2: (12, 13, 10)
Volume of Box1 : 210
Volume of Box2 : 1560
Box 3: (18, 20, 15)
Volume of Box3 : 5400
Box1 is not greater than Box2
Box1 is less than Box2
Box1 is not greater or equal to Box2
Box1 is less or equal to Box2
Box1 is not equal to Box2
Box3 is equal to Box4