朋友功能程序未产生主要功能中所需的值

Question

我希望cout语句像这样在main（）函数中产生值：

客户ID：1234

城市：加斯托尼亚

状态：北卡罗来纳州

邮政编码：28054

我假设这是一个简单的修复程序，但是我要花钱并准备扔毛巾。我在烟气上奔跑。任何帮助将不胜感激！

     #include<iostream>
#include <string>
using namespace std;

class City;
class Customer
{
private:
int customerNumber;
int zipcode;
public:
Customer(int number, int zip)
{
    customerNumber = number;
    zipcode = zip;
}
friend void display(Customer customer, City city);
};
class City
{
private:
string city;
string state;
public:
City(string C, string S)
{
    city = C;
    state = S;
}

friend void display(Customer customer, City city);
};
void display(Customer customer, City city)
{
cout << "Customer Number: " << endl;
cout << "City: " << endl;
cout << "State: " << endl;
cout << "Zip code: " << endl;
}
int main()
{
Customer customer(1234, 28054);
City city("Gastonia", "North Carolina");
display(customer, city);
return 0;

Answer 1

display实际上并未从对象访问字段。简单修复：

void display(Customer customer, City city) {
    cout << "Customer Number: " << customer.customerNumber << endl;
    cout << "City: " << city.city << endl;
    cout << "State: " << city.state << endl;
    cout << "Zip code: " <<  customer.zipcode << endl;
}