#include<iostream>
#include<string>
using namespace std;
class manage//定義manage類，完成定義后manage將成為完整的類
{
public:
	//printPerson函數(shù)的定義將使用person類對(duì)象的成員，其定義依賴于完整的person類，故此處不能定義，只能聲明，否則將產(chǎn)生循環(huán)依賴
	ostream& printPerson(ostream&)const;
};
class person//定義person類
{
	//聲明manage的成員函數(shù)printPerson為友元，需要完整的manage類，即manage類的定義
	friend ostream& manage::printPerson(ostream&)const;
public:
	person() = default;
	person(string name, unsigned int age) :m_name(name), m_age(age) {}
private:
	string m_name;
	unsigned int m_age = 0;
};
//成員函數(shù)printPerson的定義需要完整的person類
//實(shí)際上這是一個(gè)比較雞肋的函數(shù)，并沒(méi)有什么實(shí)際意義，這里更多的只是為了展示情況一下該如何組織程序結(jié)構(gòu)
ostream& manage::printPerson(ostream& os)const
{
	person p("zhenlllz", 21);
	os << p.m_name << '\t' << p.m_age;
	return os;
}
int main()
{
	manage m;
	m.printPerson(cout) << endl;//結(jié)果為 “zhenlllz	21”
	system("pause");
	return 0;
}

#include<iostream>
#include<string>
using namespace std;
class person;//向前聲明person類，person類現(xiàn)在為不完整的類
class manage//定義manage類
{
public:
	//printPerson函數(shù)的聲明至少需要不完整的person類，即person類的聲明
	//printPerson函數(shù)的定義將使用person類對(duì)象的成員，其定義依賴于完整的person類，故此處不能定義，只能聲明，否則將產(chǎn)生循環(huán)依賴
	ostream& printPerson(ostream&, const person&)const;  
};
class person//定義person類
{
	//聲明manage的成員函數(shù)printPerson為友元需要完整的manage類，即manage類的定義
	friend ostream& manage::printPerson(ostream&, const person&)const;
public:
	person() = default;
	person(string name, unsigned int age) :m_name(name), m_age(age) {}
private:
	string m_name;
	unsigned int m_age = 0;
};
//成員函數(shù)printPerson的定義需要完整的person類
ostream& manage::printPerson(ostream& os, const person& p)const		
{
	os << p.m_name << '\t' << p.m_age;
	return os;
}
int main()
{
	person p("zhenlllz", 21);
	manage m;
	m.printPerson(cout, p) << endl;//結(jié)果為 “zhenlllz	21”
	system("pause");
	return 0;
}

#include<iostream>
#include<string>
using namespace std;
class person;//向前聲明person類，person類現(xiàn)在為不完整的類
class manage//定義manage類
{
public:
	//printPerson函數(shù)的聲明至少需要不完整的person類，即person類的聲明
	//printPerson函數(shù)的定義將使用person類對(duì)象的成員，其定義依賴于完整的person類，故此處不能定義，只能聲明，否則將產(chǎn)生循環(huán)依賴
	ostream& printPerson(ostream&, const person&)const;  
};
class person//定義person類
{
	//聲明manage的成員函數(shù)printPerson為友元需要完整的manage類，即manage類的定義
	friend ostream& manage::printPerson(ostream&, const person&)const;
public:
	person() = default;
	person(string name, unsigned int age) :m_name(name), m_age(age) {}
private:
	string m_name;
	unsigned int m_age = 0;
};
//成員函數(shù)printPerson的定義需要完整的person類
ostream& manage::printPerson(ostream& os, const person& p)const		
{
	os << p.m_name << '\t' << p.m_age;
	return os;
}
int main()
{
	person p("zhenlllz", 21);
	manage m;
	m.printPerson(cout, p) << endl;//結(jié)果為 “zhenlllz	21”
	system("pause");
	return 0;
}

#include<iostream>
#include<vector>
#include<string>
using namespace std;
class person//person類的定義
{
	friend class Help;
public:
	person() = default;
	person(string name, unsigned int age) :m_name(name), m_age(age) {}
private:
	string m_name;
	unsigned int m_age = 0;
};
class Help
{
	friend class manage;
	using index = vector<person>::size_type;
    //manage類的成員函數(shù)change的實(shí)現(xiàn)
	static void doChange(person& p, string name, unsigned int age)
	{
		p.m_age = age;
		p.m_name = name;
	}
    //manage類的成員函數(shù)printPerson的實(shí)現(xiàn)
	static ostream& doPrintPerson(const person& p, ostream& os = cout)
	{
		os << p.m_name << '\t' << p.m_age;
		return os;
	}
};
class manage
{
public:
	using index = vector<person>::size_type;
	void add(const person& p) { m_v.push_back(p); } 
	inline void change(index, string, unsigned int); 
	inline void printPerson(index, ostream & = cout)const;	
	inline void printPerson(ostream & = cout)const; 
private:
	vector<person> m_v{ person("默認(rèn)",0) };
};
void manage::change(index i, string name, unsigned int age)
{
	if (i >= m_v.size())
		return;
	person& p = m_v[i];
	Help::doChange(p, name, age);
}
void manage::printPerson(index i, ostream& os)const
{
	if (i >= m_v.size())
		return;
	const person& p = m_v[i];
	Help::doPrintPerson(p, os) << endl;
}
void manage::printPerson(ostream& os)const
{
	for (auto p : m_v)
		Help::doPrintPerson(p, os) << endl;
}
int main()
{
	person p1("一號(hào)", 20);
	person p2("二號(hào)", 30);
	person p3("三號(hào)", 40);
	manage m;
	m.add(p1);
	m.add(p2);
	m.add(p3);
	m.change(2, "zhenlllz", 21);	
	m.printPerson(2, cout);
	m.printPerson();
	system("pause");
	return 0;
}