Question

可能重复：
When to use forward declaration?

我正在使用Kubuntu＆amp;蚀。

我有这两个类：

Student.h

#ifndef STUDENT_H_
#define STUDENT_H_

#include <iostream>
#include <string>
#include <vector>

#include "Course.h"

using namespace std;

class Student {
    public:
        Student(vector<string> &vec);
        virtual void study(Course &c)=0;
        virtual ~Student();
    private:
        string _studentId;
        string _department;
        string _pathToImage;
};

#endif /* STUDENT_H_ */

Course.h

#ifndef COURSE_H_
#define COURSE_H_

#include <iostream>
#include <vector>
#include <string>
#include <stdio.h>
#include <stdlib.h>

#include "Student.h"

using namespace std;
class Course {
    public:
        Course(vector<string> &vec);
        virtual void teach();
        virtual void reg(Student &s)=0;
        virtual ~Course();
    private:
        string _department;
        string _name;
        int _semester;
        int _minimumGrade;
};

#endif /* COURSE_H_ */

我在回答时遇到了这个错误：

Description Resource    Path    Location    Type
‘Course’ has not been declared  Student.h   /hw2/include    line 22 C/C++ Problem

我还有一些继承这些类的类。我认为这不是问题所在。

可能是什么问题？

由于

修改

在对您的答案进行一些编辑后，现在这是我的文件：

Course.h

#ifndef COURSE_H_
#define COURSE_H_

#include <iostream>
#include <vector>
#include <string>
#include <stdio.h>
#include <stdlib.h>

class Student;

using namespace std;
class Course {
    public:
        Course(vector<string> &vec);
        virtual void teach();
        virtual void reg(Student &s)=0;
        virtual ~Course();
    private:
        string _department;
        string _name;
        int _semester;
        int _minimumGrade;
};

#endif /* COURSE_H_ */

Student.h

#ifndef STUDENT_H_
#define STUDENT_H_

#include <iostream>
#include <string>
#include <vector>

class Course;


using namespace std;

class Student {
    public:
        Student(vector<string> &vec);
        virtual void study(Course &c)=0;
        virtual ~Student();
    private:
        string _studentId;
        string _department;
        string _pathToImage;
};

#endif /* STUDENT_H_ */

Course.cpp

#include "../include/Course.h"
#include "../include/Student.h"

Course::Course(vector<string> &vec): _department(""), _name(""), _semester(0), _minimumGrade(0) {
    _department = vec[0];
    _name = vec[1];
    _semester = atoi(vec[2].c_str());
    _minimumGrade = atoi(vec[3].c_str());
}

Course::~Course() {
    // TODO Auto-generated destructor stub
}

Student.cpp

#include "../include/Course.h"
#include "../include/Student.h"

Student::Student(vector<string> &vec): _studentId(""), _department(""), _pathToImage("") {
    _studentId = vec[0];
    _department = vec[1];
    _pathToImage = vec[2];
}
Student::~Student() {
    // TODO Auto-generated destructor stub
}

现在它给了我很多这样的错误：

Description Resource    Path    Location    Type
  required from ‘static void __gnu_cxx::__alloc_traits<_Alloc>::construct(_Alloc&, __gnu_cxx::__alloc_traits<_Alloc>::pointer, const _Tp&) [with _Tp = Student; _Alloc = std::allocator<Student>; __gnu_cxx::__alloc_traits<_Alloc>::pointer = Student*]’   hw2     line 202, external location: /usr/include/c++/4.7/ext/alloc_traits.h    C/C++ Problem
  required from ‘static void __gnu_cxx::__alloc_traits<_Alloc>::construct(_Alloc&, __gnu_cxx::__alloc_traits<_Alloc>::pointer, const _Tp&) [with _Tp = Course; _Alloc = std::allocator<Course>; __gnu_cxx::__alloc_traits<_Alloc>::pointer = Course*]’  hw2     line 202, external location: /usr/include/c++/4.7/ext/alloc_traits.h    C/C++ Problem
  required from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = Course; _Alloc = std::allocator<Course>; std::vector<_Tp, _Alloc>::value_type = Course]’   hw2     line 885, external location: /usr/include/c++/4.7/bits/stl_vector.h C/C++ Problem
  required from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = Course; _Alloc = std::allocator<Course>; std::vector<_Tp, _Alloc>::value_type = Course]’   hw2     line 893, external location: /usr/include/c++/4.7/bits/stl_vector.h C/C++ Problem
  required from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = Student; _Alloc = std::allocator<Student>; std::vector<_Tp, _Alloc>::value_type = Student]’    hw2     line 885, external location: /usr/include/c++/4.7/bits/stl_vector.h C/C++ Problem
  required from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = Student; _Alloc = std::allocator<Student>; std::vector<_Tp, _Alloc>::value_type = Student]’    hw2     line 893, external location: /usr/include/c++/4.7/bits/stl_vector.h C/C++ Problem

Answer 1

摆脱包含，而只是将class Course;放入student.h并将class Student;放入course.h中。这些类型不完整是足够的，因为你只需要函数参数（实际上你只需要引用它们）。

您现在需要将相关包含添加到.cpp文件中，例如student.cpp应以#include "student.h"和#include "course.h"开头。

Answer 2

你在这里被称为循环依赖（Student.h取决于Course.h，它取决于Student.h，取决于......）。

要解决此问题，您应该转发声明在每个头文件中使用的类。

例如，在Student.h中，您应该将#include "Course.h"替换为class Course。然后在实现文件中，您可以包含Course.h文件并使用Course对象。

如何在c ++中做相互的类

2 个答案: