为什么编译时会报错[Error] no matching function for call to 'base::base()'

[csu之c]

#include <iostream>
using namespace std;

class base{
    protected:
        string name, sex;
        int age;
    public:
        base(string nam, string se, int a){name = nam; sex = se; age = a;}
        void Setname(){cin >> name;}
        void Setsex(){cin >> sex;}
        void Setage(){cin >> age;}
        void showbase();
};
void base::showbase(){
    cout << "姓名：" << name << endl;
    cout << "性别：" << sex << endl;
    cout << "年龄：" << age << endl;
}

class teacher: virtual public base{
    private:
        string profession;
        string teanum;
    protected:
        int salary;
    public:
        teacher(string nam, string se, int a, string pro, string tnum, int s):base(nam, se, a){profession = pro; teanum = tnum; salary = s;}
        void Setprofession(){cin >> profession;}
        void Setteanum(){cin >> teanum;}
        void Setsalary(){cin >> salary;}
        void showteacher();
};
void teacher::showteacher(){
    showbase();
    cout << "工号：" << teanum << endl;
    cout << "职称：" << profession << endl;
    cout << "薪水：" << salary << endl;
}

class student: virtual public base{
    protected:
        string stunum;
        string cla;
        string major;
        int score;
    public:
        student(string nam, string se, int a, string snum, string cl, string m, int s):base(nam, se, a){stunum = snum; cla = cl; major = m; score = s;}
        void Setstunum(){cin >> stunum;}
        void Setcla(){cin >> cla;}
        void Setmajor(){cin >> major;}
        void Setscore(){cin >> score;}
        void showstudent();
};
void student::showstudent(){
    showbase();
    cout << "学号：" << stunum << endl;
    cout << "班级：" << cla << endl;
    cout << "专业：" << major << endl;
    cout << "分数：" << score << endl;
}


class master: public teacher, public student{
    protected:
        string company;
    public:
        master(string nam1, string se1, int a1, string snum, string cl, string m, int s,  string nam2, string se2, int a2, string pro, string tnum, int sa, string com)
        :teacher(nam2, se2, a2, pro, tnum, sa), student(nam1, se1, a1, snum, cl, m, s) {company = com;}
};

int main()
{
  ...
}

为什么编译时会报错[Error] no matching function for call to 'base::base()'？

[真相重于对错]

提供默认构造函数啊

[真相重于对错]

你把那两个类改成非virutal 继承就不会报错了，但是如果非虚继承的话，master类型就有两个base部分一个是从student，一个是teacher。 例如下面代码，将会输出9和10；

#include <iostream>
#include <typeinfo>
#include <iostream>
#include <string>
using namespace std;
struct Base {
	int m;
	Base(int b):m(b) {

	}
};
struct ch :public Base {
	int x;
	ch(int a):x(a),Base(a){}
};
struct bh :public Base {
	int z;
	bh(int a):z(a),Base(a-1){}
};
struct dh :public ch, public bh
{
	dh(int x):ch(x),bh(x){}
};

int main()
{
	dh d1(10);
	Base* x = static_cast<Base *>(static_cast<ch *>(&d1));
	Base* x1 = static_cast<Base *>(static_cast<bh *>(&d1));
	cout << x->m << endl;
	cout << x1->m << endl;
}

[真相重于对错]

虚拟继承话，master只有一个base部分，但是你要像他的父类一样提供如何构造，而不能直接从父类继承下来，这就是要你提供默认构造函数的原因。