操作符重载的概念
复数计算第一种形式(自定义复数类):
1 #include <stdio.h> 2 3 class Complex 4 { 5 int a; 6 int b; 7 public: 8 Complex(int a = 0, int b = 0) 9 { 10 this->a = a; 11 this->b = b; 12 } 13 14 int getA() 15 { 16 return a; 17 } 18 19 int getB() 20 { 21 return b; 22 } 23 24 friend Complex Add(const Complex& p1, const Complex& p2); 25 }; 26 27 Complex Add(const Complex& p1, const Complex& p2) 28 { 29 Complex ret; 30 31 ret.a = p1.a + p2.a; 32 ret.b = p1.b + p2.b; 33 34 return ret; 35 } 36 37 int main() 38 { 39 40 Complex c1(1, 2); 41 Complex c2(3, 4); 42 Complex c3 = Add(c1, c2); // c1 + c2 43 44 printf("c3.a = %d, c3.b = %d\n", c3.getA(), c3.getB()); 45 46 return 0; 47 }
Question:
Add 函数可以解决Complex对象相加的问题;
但是Complex是现实世界的确定存在的复数;
并且复数的地位在数学中的地位与普通的实数地位i相同;
为什么不能+操作符也支持复数相加呢?
操作符重载:
C++中的operator关键字可以定义特殊的函数
operator的本质是通过函数重载操作符;
1 #include <stdio.h> 2 3 class Complex 4 { 5 int a; 6 int b; 7 public: 8 Complex(int a = 0, int b = 0) 9 { 10 this->a = a; 11 this->b = b; 12 } 13 14 int getA() 15 { 16 return a; 17 } 18 19 int getB() 20 { 21 return b; 22 } 23 24 friend Complex operator + (const Complex& p1, const Complex& p2); 25 }; 26 27 Complex operator + (const Complex& p1, const Complex& p2) 28 { 29 Complex ret; 30 31 ret.a = p1.a + p2.a; 32 ret.b = p1.b + p2.b; 33 34 return ret; 35 } 36 37 int main() 38 { 39 40 Complex c1(1, 2); 41 Complex c2(3, 4); 42 Complex c3 = c1 + c2; // operator + (c1, c2) 43 44 printf("c3.a = %d, c3.b = %d\n", c3.getA(), c3.getB()); 45 46 return 0; 47 }
操作符重载的本质就是函数重载.
那还有什么深度挖掘的地方呢?上面的例子我们使用了友元,而友元是我们尽量避免的,那我们可以怎样修改呢?
-可以将操作符重载函数定义为类中的 成员函数.
-比全局操作符重载函数少一个参数(左操作数)
-不需要依赖友元就可以完成操作符重载;
-编译器优先在成员函数中寻找操作符操作函数;
实例代码分析3:
1 #include <stdio.h> 2 3 class Complex 4 { 5 int a; 6 int b; 7 public: 8 Complex(int a = 0, int b = 0) 9 { 10 this->a = a; 11 this->b = b; 12 } 13 14 int getA() 15 { 16 return a; 17 } 18 19 int getB() 20 { 21 return b; 22 } 23 24 Complex operator + (const Complex& p) 25 { 26 Complex ret; 27 printf("Complex operator + (const Complex& p)\n"); 28 ret.a = this->a + p.a; 29 ret.b = this->b + p.b; 30 31 return ret; 32 } 33 34 friend Complex operator + (const Complex& p1, const Complex& p2); 35 }; 36 37 Complex operator + (const Complex& p1, const Complex& p2) 38 { 39 Complex ret; 40 printf("Complex operator + (const Complex& p1, const Complex& p2)\n"); 41 ret.a = p1.a + p2.a; 42 ret.b = p1.b + p2.b; 43 44 return ret; 45 } 46 47 int main() 48 { 49 50 Complex c1(1, 2); 51 Complex c2(3, 4); 52 Complex c3 = c1 + c2; // c1.operator + (c2) 53 54 printf("c3.a = %d, c3.b = %d\n", c3.getA(), c3.getB()); 55 56 return 0; 57 }
小结:
操作符重载是C++的强大特性之一;
操作符重载的本质是通过函数扩展操作符的功能;
operator关键字是实现操作符重载的关键
操作符重载遵循相同的函数重载规则
全局函数和成员函数都可以实现对操作符的重载.
