在 C# 中，大多数内置的操作符都是可以被重定义的。因此，程序员也可以为自定义类型使用这些操作符。重载的操作符实际上是特殊名称的函数——关键字 operator 后跟要定义的操作符符号。像任何其他函数一样，重载的操作符也有返回类型和参数列表。
例如，下面是一个函数示例：
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;
}
上述函数实现了用户定义的类 Box 的加法操作符 (+)。它将两个 Box 对象的属性相加，并返回结果的 Box 对象。
实现操作符重载
下面的程序展示了完整的实现：
using System;
namespace OperatorOvlApplication {
class Box {
private double length;
private double breadth;
private double height;
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;
}
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();
Box Box2 = new Box();
Box Box3 = new Box();
double volume = 0.0;
Box1.setLength(6.0);
Box1.setBreadth(7.0);
Box1.setHeight(5.0);
Box2.setLength(12.0);
Box2.setBreadth(13.0);
Box2.setHeight(10.0);
volume = Box1.getVolume();
Console.WriteLine("Volume of Box1 : {0}", volume);
volume = Box2.getVolume();
Console.WriteLine("Volume of Box2 : {0}", volume);
Box3 = Box1 + Box2;
volume = Box3.getVolume();
Console.WriteLine("Volume of Box3 : {0}", volume);
Console.ReadKey();
}
}
}
当上述代码被编译和执行时，会产生如下结果：
Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400
可重载与不可重载的操作符
下表描述了 C# 中操作符的重载能力：
| 序号 |
操作符 & 描述 |
| 1 |
+, -, !, ~, ++, -- |
| |
这些一元操作符需要一个操作数，并且可以被重载。 |
| 2 |
+, -, *, /, % |
| |
这些二元操作符需要一个操作数，并且可以被重载。 |
| 3 |
==, !=, <, >, <=, >= |
| |
比较操作符可以被重载。 |
| 4 |
&&, |
| |
条件逻辑操作符不能直接被重载。 |
| 5 |
+=, -=, *=, /=, %= |
| |
赋值操作符不能被重载。 |
| 6 |
=, ., ? :, ->, new, is, sizeof, typeof |
| |
这些操作符不能被重载。 |
示例
根据上述讨论，让我们扩展前面的例子，并重载一些更多的操作符：
using System;
namespace OperatorOvlApplication {
class Box {
private double length;
private double breadth;
private double height;
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;
}
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();
Box Box2 = new Box();
Box Box3 = new Box();
Box Box4 = new Box();
double volume = 0.0;
Box1.setLength(6.0);
Box1.setBreadth(7.0);
Box1.setHeight(5.0);
Box2.setLength(12.0);
Box2.setBreadth(13.0);
Box2.setHeight(10.0);
Console.WriteLine("Box 1: {0}", Box1.ToString());
Console.WriteLine("Box 2: {0}", Box2.ToString());
volume = Box1.getVolume();
Console.WriteLine("Volume of Box1 : {0}", volume);
volume = Box2.getVolume();
Console.WriteLine("Volume of Box2 : {0}", volume);
Box3 = Box1 + Box2;
Console.WriteLine("Box 3: {0}", Box3.ToString());
volume = Box3.getVolume();
Console.WriteLine("Volume of Box3 : {0}", volume);
if (Box1 > Box2)
Console.WriteLine("Box1 is greater than Box2");
else
Console.WriteLine("Box1 is not 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();
}
}
}
当上述代码被编译和执行时，会产生如下结果：
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