//namespace.h
#include <string>

namespace pers
{
    struct Person
    {
        std::string fname;
        std::string lname;
    };

    void getPerson (Person &);
    void showPerson (Person &);
}

namespace debts
{
    using namespace pers;

    struct Debt
    {
        Person name;
        double amount;
    };

    void getDebt (Debt &);
    void showDebt (Debt &);
    double sumDebts (const Debt ar[],int n);
}

//namesp.cpp
#include <iostream>
#include "namespace.h"

namespace pers
{
    using std::cout;
    using std::cin;
    using std::endl;

    void getPerson (Person &rp)
    {
        cout << "Enter the first name  : ";
        cin >> rp.fname;
        cout << endl;

        cout << "Enter the last name : ";
        cin >> rp.lname;
        cout << endl;
    }

    void showPerson (const Person &rp)
    {
        cout << rp.lname << " and " << rp.fname;
        cout << endl;
    }
}

namespace debts
{
    using std::cout;
    using std::cin;
    using std::endl;
    using pers::getPerson;
    using pers::showPerson;


    void getDebt (Debt &rd)
    {
        getPerson (rd.name);
        cout << "Enter debt :";
        cin >> rd.amount;
    }

    void showDebt (const Debt &rd)
    {
        showPerson (rd.name);
        cout << " $" << rd.amount << endl;
    }

    double sumDebts (const Debt ar[],int n)
    {
        double total = 0;
        for (int i = 0;i < n;i++)
        {
            total += ar[i].amount;
        }

        return total;
    }
}

//main.cpp 
#include <iostream>
#include "namespace.h"

void other (void);
void another (void);

int main ()
{
    using debts::Debt;
    using debts::showDebt;

    Debt golf = {{"Benny","Goatsniff"},120.0};
    showDebt (golf);
    other ();
    another ();
    return 0;
}

void other (void)
{
    using std :: cout;
    using std :: cin;
    using std :: endl;


    using namespace debts;

    Person dg = {"Doodles","Glister"};
    showPerson (dg);
    
    cout << endl;
    Debt zippy[3];

    int i = 0;
    for (i = 0;i < 3;i++)
    {
        getDebt (zippy[i]);
    }

    for (i = 0;i < 3;i++)
    {
        showDebt (zippy[i]);
    }

    cout << "Total debt : $" <<sumDebts (zippy,3) << endl;
    return ;
}

void another (void)
{
    using pers::Person;

    Person collector = {"Milo","Rightshitf"};
    pers::showPerson (collector);
    std::cout << std::endl;
    
    return ;
}

编译器错误提示：>main.obj : error LNK2019: 无法解析的外部符号 "void __cdecl debts::showDebt(struct debts::Debt &)" (?showDebt@debts@@YAXAAUDebt@1@@Z)，该符号在函数 _main 中被引用
1>main.obj : error LNK2019: 无法解析的外部符号 "void __cdecl pers::showPerson(struct pers::Person &)" (?showPerson@pers@@YAXAAUPerson@1@@Z)，该符号在函数 "void __cdecl other(void)" (?other@@YAXXZ) 中被引用
1>E:\Code\code from C++ Primer Plus\名称空间示例代码\Debug\名称空间示例代码.exe : fatal error LNK1120: 2 个无法解析的外部命令


这是怎么回事啊，查资料查不到。。

这种问题，提示已经说得很清楚了，下次不要问了

比如编译器说找不到 void __cdecl debts::showDebt(struct debts::Debt &)
你自己查一下代码，确实没有，你声明了 void showDebt (Debt &);
但根本没有 void showDebt (Debt &rd) 的实现，只有 void showDebt (const Debt &rd) 的实现