链接错误C++继承

Question

我有两个班级: Person和Student。我目前正在尝试从Person类派生出Student类。

但是，我一直收到一个链接错误。

错误：

[Linker error] undefined reference to `Person::Person()' 

我的代码：

#include <iostream> 
#include <iomanip>
using namespace std; 

class Person { 

  string Name ;

public: 
  Person(void);

  void set(){ 

       cout << "Name:" << endl ;
       cin >> Name ; 
       } 

  string get_Name(){ 
      return Name ; 
      } 


};

class Student:Person { 
  int x, Lab1, Lab2, Lab3, Lab4, Lab5, Lab6, LabPoints, Midterm, Final ;
  float LabAvg, ExamAvg, Prcnt ; 
  string StuName ;

public: 
  Student(void);

  void set(int i){ 
       x = i; 

       cout << "Student " << x << endl << endl ;
       cout << "Name:" << endl ;
       cin >> StuName ;
       cout << "Lab 1 score (1-10): " << endl ;
       cin >> Lab1 ;
       cout << "Lab 2 score (1-10): " << endl ;
       cin >> Lab2 ;
       cout << "Lab 3 score (1-10): " << endl ;
       cin >> Lab3 ;
       cout << "Lab 4 score (1-10): " << endl ;
       cin >> Lab4 ;
       cout << "Lab 5 score (1-10): " << endl ;
       cin >> Lab5 ;
       cout << "Lab 6 score (1-10): " << endl ;
       cin >> Lab6 ;
       cout << "Midterm score (1-100): " << endl ;
       cin >> Midterm ;
       cout << "Final score (1-100): " << endl ;
       cin >> Final ;

       LabAvg = (Lab1 + Lab2) / 2.0 ;
       LabPoints = (Lab1 + Lab2) ; 
       ExamAvg = (Midterm + Final) / 2.0 ;
       Prcnt = (( ( LabPoints / 60.0 ) * 0.6 ) + ( ( Midterm / 100.0 ) * 0.2) + 
       ( ( Final / 100.0 ) * 0.2)) * 100 ;

       } 

  string get_StuName(){ 
      return StuName ; 
      } 

  int get_Lab1(){ 
      return Lab1 ; 
      } 

  int get_Lab2(){ 
      return Lab2 ; 
      } 

  int get_Lab3(){ 
      return Lab3 ; 
      } 

  int get_Lab4(){ 
      return Lab4 ; 
      } 

  int get_Lab5(){ 
      return Lab5 ; 
      } 

  int get_Lab6(){ 
      return Lab6 ; 
      } 

  float get_LabAvg(){ 
      return LabAvg ; 
      } 

  int get_LabPoints(){
      return LabPoints ; 
      } 

  float get_ExamAvg(){
      return ExamAvg ;
      } 

  float get_Prcnt(){
      return Prcnt ; 
      }
};

Student::Student(void){
  x = 0, Lab1 = 0, Lab2 = 0, Lab3 = 0, Lab4 = 0, Lab5 = 0, Lab6 = 0, 
  LabPoints = 0, Midterm = 0, Final = 0 ; 
  LabAvg = 0.0, ExamAvg = 0.0, Prcnt = 0.0 ; 
  StuName = "" ;
}

int main(){ 
  int MaxNumStu = 10, NumOfRep , i ; 
  float FPrcnt ; 
  string LetGrd ; 

  cout << "Number of Students:" << endl ;
  cin >> NumOfRep ; 
  cout << endl << endl ;

  Student obs[MaxNumStu] ; 

  NumOfRep = ++NumOfRep ;
  for(i=1 ; i < NumOfRep ; i++) 
    obs[i].set(i) ; 

  cout << endl << "---------------------------------" << endl << endl ; 

  for(i=1; i < NumOfRep; i++){
    cout << obs[i].get_StuName() << endl << endl; 
    cout << "Lab 1 Score: " << obs[i].get_Lab1() << endl ;
    cout << "Lab 2 Score: " << obs[i].get_Lab2() << endl ;
    cout << "Lab 3 Score: " << obs[i].get_Lab3() << endl ;
    cout << "Lab 4 Score: " << obs[i].get_Lab4() << endl ;
    cout << "Lab 5 Score: " << obs[i].get_Lab5() << endl ;
    cout << "Lab 6 Score: " << obs[i].get_Lab6() << endl ;
    cout << endl << "Average Lab Score: " << setprecision(4) << 
    obs[i].get_LabAvg() << endl ; 
    cout << "Total Lab Points: " << obs[i].get_LabPoints() << endl ;
    cout << endl << "Average Exam Score: " << setprecision(4) << 
    obs[i].get_ExamAvg() << endl ; 

    FPrcnt = obs[i].get_Prcnt() ;

    if ( FPrcnt >= 90 )
         LetGrd = "% A" ;
    if ( FPrcnt >= 80 )
         if ( FPrcnt < 90 )
            LetGrd = "% B" ;
    if ( FPrcnt >= 70 )
         if ( FPrcnt < 80 )
            LetGrd = "% C" ;
    if ( FPrcnt >= 60 )
         if ( FPrcnt < 70 )
            LetGrd = "% D" ;
    if ( FPrcnt < 60 )
         LetGrd = "% F";

    cout << endl << endl << "Overall Grade: " << setprecision(3) << FPrcnt 
    << LetGrd << endl;
    cout << endl << endl ; 
    }
  system( "pause" ) ;
}

Answer 1

您已经为Person声明了一个默认构造函数

public: 
  Person(void);

但从未定义过它。

在这种情况下，您不需要拥有自己的默认构造函数-删除声明，让编译器为您生成一个默认构造函数。或者，您可以定义一个不做任何事情：

Person::Person()
{
}

Answer 2

您在未定义的情况下声明了Person::Person(void);。

如果您删除了这一行，您将会很好。

Answer 3

您在第10行声明了Person::Person()，但从未定义过它。