学习C++——只声明忘记定义了

#include <iostream>
#include <list>
#include <string>

using namespace std;
class Employee
{
    string family_name;
    short department;
public:
    Employee(const string& name,int dept);
    virtual void print() const;
};
Employee::Employee(const string& name,int dept):family_name(name),department(dept){}
void Employee::print() const
{
    cout << family_name << '\t' << department << endl;
}

class Manager:public Employee
{
    list<Employee*> group;
    short level;
public:
    Manager(const string& name,int dept,int lvl);
    void print() const;
};
Manager::Manager(const string& name,int dept,int lvl):Employee(name,dept),level(lvl){}
void Manager::print() const
{
    Employee::print();
    cout << "\tlevel" << level << endl;
}
void print_list(const list<Employee*>& s)
{
    for(list<Employee*>::const_iterator p=s.begin();p!=s.end();++p)
        (*p)->print();
}

int main()
{
    //cout << "Hello world!" << endl;
    Employee e("Brown",);
    Manager  m("Smith",,);
    list<Employee*> empl;
    empl.push_front(&e);
    empl.push_front(&m);
    print_list(empl);
    return ;
}

废话少说，直接上代码；红色部分，就是当初自己以为是声明定义的，但是后来才发现，我居然把声明当定义来用，硬伤啊。