关于构造函数的一点理解

source code：

base class：

class persion 
{
protected:
 string _name,_sex,_birthday,_number;
 int _age;
public:
 persion(string st_name,string st_sex,string st_birthday,int st_age,string st_number);
 persion(){}
 virtual bool SearchData(string studentnumber,string name)=0; 

 void DisplayData();  };

derived class：

class Student:virtual public persion
{
private:

 string _major;
 string _electiveslesson;
 int _electivessore;  
public: 
 int basesore[3];
 Student(){}
 Student(string st_name,string st_sex,string st_birthday,int st_age,string st_number);//report student information
 Student(string st_major,int st_chinese,int st_math,int st_english,string st_electiveslesson,int st_electivessore);
      
 bool SearchData(string studentnumber,string name);    
 void DisplayStudentData();         };

Student::Student(string st_name,string st_sex,string st_birthday,int st_age,string st_number)
:persion(st_name,st_sex,st_birthday,st_age,st_number)
{
}
Student::Student(string st_major,int st_chinese,int st_math,int st_english,string st_electiveslesson,int st_electivessore)
{  
 
 _major= st_major;
 basesore[0]=st_chinese;
 basesore[1]=st_math;
 basesore[2]=st_english;
 _electiveslesson=st_electiveslesson;
 _electivessore=st_electivessore;
}

bool Student::SearchData(string studentnumber,string name)  
{
 if(string(name)==string(_name)||string(studentnumber)==string(_number))
 {                        
  cout<<"search success!"<<endl;
  return true;
 }
 else
  return false;
} 
void Student::DisplayStudentData()            
{
 cout<<"major\t"<<"Chinese\t"<<"math\t"<<"English\t"<<"elective\t"<<"elective score"<<endl;
 cout<<_major<<"\t";
 for(int i=0;i<3;i++)
  cout<<basesore[i]<<"\t ";
 cout<<_electiveslesson<<"\t\t"<<_electivessore<<endl;
}

  case 1:
       {
        cout<<"Please input number,name: ";
        cin>>number>>name;
                          for(x=0;x<st_num;x++)
        {
         if (st_infor[x].SearchData(number,name)==true)
         {
          st_infor[x].DisplayData();
          score_infor[x].DisplayStudentData();
          break;
         }
        
         }
         if(x==st_num)
         cout<<"search no report!"<<endl;
        break;
          }