C# 程序員參考--運算符重載教程

本教程演示用戶定義的類如何重載運算符。

示例文件

請參見“運算符重載”示例以下載和生成本教程中討論的示例文件。
教程

運算符重載允許為運算指定用戶定義的運算符實現，其中一個或兩個操作數是用戶定義的類或結構類型。本教程包含兩個示例。第一個示例展示如何使用運算符重載創建定義復數加法的復數類。第二個示例展示如何使用運算符重載實現三值的邏輯類型。

示例 1

本示例展示如何使用運算符重載創建定義復數加法的復數類 Complex。本程序使用 ToString 方法的重載顯示數字的虛部和實部以及加法結果。

// complex.csusing System;public struct Complex {   public int real;   public int imaginary;   public Complex(int real, int imaginary)    {      this.real = real;      this.imaginary = imaginary;   }   // Declare which operator to overload (+), the types    // that can be added (two Complex objects), and the    // return type (Complex):   public static Complex operator +(Complex c1, Complex c2)    {      return new Complex(c1.real + c2.real, c1.imaginary + c2.imaginary);   }   // Override the ToString method to display an complex number in the suitable format:   public override string ToString()   {      return(String.Format("{0} + {1}i", real, imaginary));   }   public static void Main()    {      Complex num1 = new Complex(2,3);      Complex num2 = new Complex(3,4);      // Add two Complex objects (num1 and num2) through the      // overloaded plus operator:      Complex sum = num1 + num2;     // Print the numbers and the sum using the overriden ToString method:      Console.WriteLine("First complex number:  {0}",num1);      Console.WriteLine("Second complex number: {0}",num2);      Console.WriteLine("The sum of the two numbers: {0}",sum);    }}

輸出

First complex number:  2 + 3iSecond complex number: 3 + 4iThe sum of the two numbers: 5 + 7i

示例 2

本示例展示如何使用運算符重載實現三值的邏輯類型。該類型的可能值有 DBBool.dbTrue、DBBool.dbFalse 和 DBBool.dbNull，其中 dbNull 成員表示未知值。

注意   定義 True 和 False 運算符只對表示 True、False 和 Null（既非 True 也非 False）的類型有用，如數據庫中使用的類型。

// dbbool.csusing System;public struct DBBool{   // The three possible DBBool values:   public static readonly DBBool dbNull = new DBBool(0);   public static readonly DBBool dbFalse = new DBBool(-1);   public static readonly DBBool dbTrue = new DBBool(1);   // Private field that stores -1, 0, 1 for dbFalse, dbNull, dbTrue:   int value;    // Private constructor. The value parameter must be -1, 0, or 1:   DBBool(int value)    {      this.value = value;   }   // Implicit conversion from bool to DBBool. Maps true to    // DBBool.dbTrue and false to DBBool.dbFalse:   public static implicit operator DBBool(bool x)    {      return x? dbTrue: dbFalse;   }   // Explicit conversion from DBBool to bool. Throws an    // exception if the given DBBool is dbNull, otherwise returns   // true or false:   public static explicit operator bool(DBBool x)    {      if (x.value == 0) throw new InvalidOperationException();      return x.value > 0;   }   // Equality operator. Returns dbNull if either operand is dbNull,    // otherwise returns dbTrue or dbFalse:   public static DBBool operator ==(DBBool x, DBBool y)    {      if (x.value == 0 || y.value == 0) return dbNull;      return x.value == y.value? dbTrue: dbFalse;   }   // Inequality operator. Returns dbNull if either operand is   // dbNull, otherwise returns dbTrue or dbFalse:   public static DBBool operator !=(DBBool x, DBBool y)    {      if (x.value == 0 || y.value == 0) return dbNull;      return x.value != y.value? dbTrue: dbFalse;   }   // Logical negation operator. Returns dbTrue if the operand is    // dbFalse, dbNull if the operand is dbNull, or dbFalse if the   // operand is dbTrue:   public static DBBool operator !(DBBool x)    {      return new DBBool(-x.value);   }   // Logical AND operator. Returns dbFalse if either operand is    // dbFalse, dbNull if either operand is dbNull, otherwise dbTrue:   public static DBBool operator &(DBBool x, DBBool y)    {      return new DBBool(x.value < y.value? x.value: y.value);   }   // Logical OR operator. Returns dbTrue if either operand is    // dbTrue, dbNull if either operand is dbNull, otherwise dbFalse:   public static DBBool operator |(DBBool x, DBBool y)    {      return new DBBool(x.value > y.value? x.value: y.value);   }   // Definitely true operator. Returns true if the operand is    // dbTrue, false otherwise:   public static bool operator true(DBBool x)    {      return x.value > 0;   }   // Definitely false operator. Returns true if the operand is    // dbFalse, false otherwise:   public static bool operator false(DBBool x)    {      return x.value < 0;   }   // Overload the conversion from DBBool to string:   public static implicit operator string(DBBool x)    {      return x.value > 0 ? "dbTrue"           : x.value < 0 ? "dbFalse"           : "dbNull";   }   // Override the Object.Equals(object o) method:   public override bool Equals(object o)    {      try       {         return (bool) (this == (DBBool) o);      }      catch       {         return false;      }   }   // Override the Object.GetHashCode() method:   public override int GetHashCode()    {      return value;   }   // Override the ToString method to convert DBBool to a string:   public override string ToString()    {      switch (value)       {         case -1:            return "DBBool.False";         case 0:            return "DBBool.Null";         case 1:            return "DBBool.True";         default:            throw new InvalidOperationException();      }   }}class Test {   static void Main()    {      DBBool a, b;      a = DBBool.dbTrue;      b = DBBool.dbNull;      Console.WriteLine( "!{0} = {1}", a, !a);      Console.WriteLine( "!{0} = {1}", b, !b);      Console.WriteLine( "{0} & {1} = {2}", a, b, a & b);      Console.WriteLine( "{0} | {1} = {2}", a, b, a | b);      // Invoke the true operator to determine the Boolean       // value of the DBBool variable:      if (b)         Console.WriteLine("b is definitely true");      else         Console.WriteLine("b is not definitely true");      }}

輸出

!DBBool.True = DBBool.False!DBBool.Null = DBBool.NullDBBool.True & DBBool.Null = DBBool.NullDBBool.True | DBBool.Null = DBBool.Trueb is not definitely true

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