我正在和Deitel的书一起学习C ++。我正在尝试编译运算符重载示例,但它失败了。你能解释一下为什么吗?这是代码:
班级原型:
// PhoneNumber class definition
#include <iostream>
#include <string>
#ifndef PHONENUMBER_H
#define PHONENUMBER_H
class PhoneNumber
{ // Start class PhoneNumber
friend std::ostream & operator<<( std::ostream &output, const PhoneNumber &number );
friend std::istream & operator>>( std::istream &input, PhoneNumber &number);
private:
// 3-digit area code
std::string areaCode;
// 3-digit exchange
std::string exchange;
// 4-digit line
std::string line;
}; // End Class PhoneNumber
#endif // PHONENUMBER_H
班级定义:
// Overloaded stream insertion and stream extraction operators
// for class PhoneNumber
#include <iomanip>
#include "phonenumber.h"
using namespace std;
// overloaded stream insertion operator; can't be
// a member function if we would like to invoke it with
// cout << somePhoneNumber;
ostream & operator <<( ostream &output, const PhoneNumber &number )
{ // Start operator<<()
output << "(" << number.areaCode << ") " << number.exchange < "-" << number.line;
return output; // enables cout << a << b << c;
} // End operator<<()
// overloaded stream extraction operator; can't be
// a member function if we would like to invoke it with
// cin >> somePhoneNumber
istream & operator >>( istream &input, PhoneNumber &number )
{ // Start operator>>()
// skip (
input.ignore();
// input area code
input >> setw( 3 ) >> number.areaCode;
// skip ) and space
input.ignore( 2 );
// input exchange
input >> setw( 3 ) >> number.exchange;
// skip dash(-)
input.ignore();
// input line
input >> setw( 4 ) >> number.line;
return input; // enables cin >> a >> b >> c;
} // end operator>>()
测试功能:
// Demonstrating class PhoneNumber's overloaded stream insertion
// and stream extraction operators
#include <iostream>
#include "phonenumber.h"
using namespace std;
int main(int argc, char *argv[])
{
PhoneNumber phone; // create object phone
cout << "Enter phone number in the form (123) 456-7890:" << endl;
// cin >> phone invokes operator>> by implicitly issuing
// the non-member function call operator>>(cin, phone )
cin >> phone;
cout << "The phone number entered was: ";
// cout << phone invokes operator<< by implicitly issuing
// the non-member function call operator<<( cout, phone)
cout << phone << endl;
return 0;
}
当我尝试构建它时,我收到一条错误消息:
phonenumber.cpp:13: error: no match for ‘operator<<’ (operand types are ‘const char [2]’ and ‘const string {aka const std::__cxx11::basic_string<char>}’)
output << "(" << number.areaCode << ") " << number.exchange < "-" << number.line;
请问您能解释一下错误的原因是什么?
答案 0 :(得分:2)
你有一个简单的拼写错误:
output << "(" << number.areaCode << ") " << number.exchange < "-" << number.line;
具体做法是:
number.exchange < "-"
应该是:
number.exchange << "-"
编译器认为您正在尝试在两个字符串上使用<
运算符。只需修理线路即可。
我系统上给我的错误信息是:
main.cpp:30:71: error: no match for 'operator<<' (operand types are 'const char [2]' and 'const string {aka const std::__cxx11::basic_string<char>}')
output << "(" << number.areaCode << ") " << number.exchange < "-" << number.line;
~~~~^~~~~~~~~~~~~~