Question

我最近开始学习面向对象的编程..对于以下代码，我收到链接器错误!!

#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;

class person{
    public:
        string name;
        person();
        person(string n){
            name = n ;
        }

        void setName(string k){
            name = k;
        }
        string getName(){
            return name;
        }
};
class student : public  person {
    public:
        string major;
        void setMajor(string m){
            major = m;
        }
        string getMajor(){
            return major;
        }
};
class faculty : public person{
    public:
        string department;
        faculty(string dept){
            department = dept;
        }
        void setDepartment(string depart){
            department = depart;
        }
        string getDepartment(){
            return department;
        }
};

int main() {

    student s;

    s.setName("james");
    s.setMajor("computer science");

    string p = s.getName();
    string p2 = s.getMajor();

    cout << "student name and mjor is :" << p << p2 << endl;
    faculty f("nanotech");
    f.setName("chris");
    f.setDepartment("electrical");
    string f1 = f.getName();
    string f2 = f.getDepartment();
    cout << "facult name and department :" << f1 << f2 << endl;

    return 0;
}

当我尝试编译代码时，我得到以下错误。

/tmp/ccYHu2de.o: In function `faculty::faculty(std::string)':
person.cpp:(.text._ZN7facultyC2ESs[_ZN7facultyC5ESs]+0x19): undefined reference to `person::person()'
/tmp/ccYHu2de.o: In function `student::student()':
person.cpp:(.text._ZN7studentC2Ev[_ZN7studentC5Ev]+0x15): undefined reference to `person::person()'
collect2: error: ld returned 1 exit status

Answer 1

在你的班级中，你有一个声明但未定义的构造函数。编译器允许您编译类，但链接器会查找实现（称为forward declaration）：

class person{
   public:
      string name;
      person();        //constructor only declared
      person(string n){
          name = n ;
     }
     .....    
 };

问题是你从学生和教职员工那里继承，你使用默认的构造函数，但你从未实现它。尝试添加实现，链接器错误将消失：

class person{
       public:
          string name;
          person(){}        //constructor implemented
          person(string n){
              name = n ;
         }
         .....    
     };

Answer 2

问题是你需要实现person类的构造函数，试试这段代码：http://ideone.com/NfXP7R

#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;

class person{
    public:
        string name;
        person() {

        }
        person(string n){
            name = n ;
        }

        void setName(string k){
            name = k;
        }
        string getName(){
            return name;
        }
};
class student : public  person {
    public:
        string major;
        void setMajor(string m){
            major = m;
        }
        string getMajor(){
            return major;
        }
};
class faculty : public person{
    public:
        string department;
        faculty(string dept){
            department = dept;
        }
        void setDepartment(string depart){
            department = depart;
        }
        string getDepartment(){
            return department;
        }
};

int main() {

    student s;

    s.setName("james");
    s.setMajor("computer science");

    string p = s.getName();
    string p2 = s.getMajor();

    cout << "student name and mjor is :" << p << p2 << endl;
    faculty f("nanotech");
    f.setName("chris");
    f.setDepartment("electrical");
    string f1 = f.getName();
    string f2 = f.getDepartment();
    cout << "facult name and department :" << f1 << f2 << endl;

    return 0;
}

跟随c ++代码获取链接器错误

2 个答案: