1. 问题
在C++中,在进行输入输出操作时,我们首先会想到用cout, cin这两个库操作语句来实现,比如
cout << 8 << “hello world!” << endl;
cin >> s;
cout,cin分别是库ostream, istream里的类对象
如果想要cout,cin来输出或输入一个类对象,这样的需求它能满足吗?很显然,原来的cout不太可能满足直接输入输出一个我们自定义的类对象,
但是只要我们对<<, >>操作符进行重载就可以让它处理自定义的类对象了。
2. 实现
有一复数类:
class Complex {
priate:
int real;
int imag;
public:
Complex(int r=, int i=):real(r),imag(i) {
cout << real << " + " << imag << "i" ;
cout << "complex class constructed."
}
}
int main() {
Complex c; // output : 0+0i, complex class constructed.
cout << c ; // error
return 0;
}
之所以上面main函数中 cout << c会出错,是因为 cout本身不支持类对象的处理,如果要让它同样能打印类对象,必须得重载操作符<<.
#include <iostream>
#include <string>class Complex {
priate:
int real;
int imag;
public:
Complex(int r=, int i=):real(r),imag(i) {
cout << real << " + " << imag << "i" ;
cout << "complex class constructed."
}
// overload global function
friend ostream & operator<<(ostream & o, const Complex & c);
friend istream & operator >> (istream & i, Complex & c);
}ostream & operator<<(ostream & o, const Complex & c) {
o<< c.real << "+" << c.imag << "i";
return o;
}istream & operator >> (istream & i, Complex & c){
string s;
i >> s; // simillar to cin >> s; input string format like as a+bi
... // parse s and get the real and imag
c. real = real;
c.imag = imag;
return i;
}
重载了操作符 <<, >> 运算后, 就可以对类Complex直接进行 输入输出操作了,比如
int main{
Complex c, c1;
cin >> c; //input : 3+4i
cout << c <<";" << c1 << " complex output."; // output : 3+4i; 0+0i complex output.
}