语法格式

类型转换函数也没有参数，因为要将当前类的对象转换为其它类型，所以参数不言而喻

  1. operator type(){
  2.     //TODO:
  3.     return data;
  4. }

示例

将Complex类型转换为double

  1. #include <iostream>
  2. using namespace std;
  4. //复数类
  5. class Complex{
  6.     public:
  7.     Complex(): m_real(0.0), m_imag(0.0){ }
  8.     Complex(double real, double imag): m_real(real), m_imag(imag){ }
  9.     public:
  10.     friend ostream & operator<<(ostream &out, Complex &c);
  11.     friend Complex operator+(const Complex &c1, const Complex &c2);
  12.     operator double() const { return m_real; }  //类型转换函数
  13.     private:
  14.     double m_real;  //实部
  15.     double m_imag;  //虚部
  16. };
  18. //重载>>运算符
  19. ostream & operator<<(ostream &out, Complex &c){
  20.     out << c.m_real <<" + "<< c.m_imag <<"i";;
  21.     return out;
  22. }
  23. //重载+运算符
  24. Complex operator+(const Complex &c1, const Complex &c2){
  25.     Complex c;
  26.     c.m_real = c1.m_real + c2.m_real;
  27.     c.m_imag = c1.m_imag + c2.m_imag;
  28.     return c;
  29. }
  31. int main(){
  32.     Complex c1(24.6, 100);
  33.     double f = c1;  //相当于 double f = Complex::operator double(&c1);
  34.     cout<<"f = "<<f<<endl;
  36.     f = 12.5 + c1 + 6;  //相当于 f = 12.5 + Complex::operator double(&c1) + 6;
  37.     cout<<"f = "<<f<<endl;
  39.     int n = Complex(43.2, 9.3);  //先转换为 double，再转换为 int
  40.     cout<<"n = "<<n<<endl;
  42.     return 0;
  43. }