一.转换构造函数
将其它类型转换为当前类类型需要借助转换构造函数(Conversion constructor)。转换构造函数也是一种构造函数,它遵循构造函数的一般规则。转换构造函数只有一个参数。
#include <iostream>
using namespace std;
//复数类
class Complex{
public:
Complex(): m_real(0.0), m_imag(0.0){ }
Complex(double real, double imag): m_real(real), m_imag(imag){ }
Complex(double real): m_real(real), m_imag(0.0){ } //转换构造函数
public:
friend ostream & operator<<(ostream &out, Complex &c); //友元函数
private:
double m_real; //实部
double m_imag; //虚部
};
//重载>>运算符
ostream & operator<<(ostream &out, Complex &c){
out << c.m_real <<" + "<< c.m_imag <<"i";;
return out;
}
int main(){
Complex a(10.0, 20.0);
cout<<a<<endl;
a = 25.5; //调用转换构造函数
cout<<a<<endl;
return 0;
}
运行结果:
10 + 20i
25.5 + 0i
二.类型转换函数
#include <iostream>
using namespace std;
//复数类
class Complex{
public:
Complex(): m_real(0.0), m_imag(0.0){ }
Complex(double real, double imag): m_real(real), m_imag(imag){ }
public:
friend ostream & operator<<(ostream &out, Complex &c);
friend Complex operator+(const Complex &c1, const Complex &c2);
operator double() const { return m_real; } //类型转换函数
private:
double m_real; //实部
double m_imag; //虚部
};
//重载>>运算符
ostream & operator<<(ostream &out, Complex &c){
out << c.m_real <<" + "<< c.m_imag <<"i";;
return out;
}
//重载+运算符
Complex operator+(const Complex &c1, const Complex &c2){
Complex c;
c.m_real = c1.m_real + c2.m_real;
c.m_imag = c1.m_imag + c2.m_imag;
return c;
}
int main(){
Complex c1(24.6, 100);
double f = c1; //相当于 double f = Complex::operator double(&c1);
cout<<"f = "<<f<<endl;
f = 12.5 + c1 + 6; //相当于 f = 12.5 + Complex::operator double(&c1) + 6;
cout<<"f = "<<f<<endl;
int n = Complex(43.2, 9.3); //先转换为 double,再转换为 int
cout<<"n = "<<n<<endl;
return 0;
}
运行结果:
f = 24.6
f = 43.1
n = 43
注意:最好不要同时使用转换构造函数和类型转换函数,因为这样会导致语义的二义性。
原文链接: https://www.cnblogs.com/yongdaimi/p/7123124.html
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