C++ pointers, Struct, and Vectors

[Daniel T. Williams]

I have an assignment to work on that I don't understand. Would appreciate any assistance to get me headed in the right direction. The instructions for this are:

Define a structure Student with a name and a vector<Course*> of courses.
• Define a structure Course with a name and a vector<Student*> of enrolled students.
• Define a function void print_student(Student* s) that print the name of a student and the names of all courses that the student takes.
• Define a function void print_course(Course* c) the prints the name of a course and the names of all students in that course.
• Define a function void enroll(Student* s, Course* c) that enrolls the given student in the given course, updating both vectors.
Note: because the Student structure refers to Course, and Course refers to Student, you'll need to use a structure declaration (aka—a forward reference) to allow you to write the definitions in the header file.

This is what I have in my header file:

struct Student;

struct Course 
{
	string name;
	vector<Student*> s;
};

struct Student
{
	string name;
	vector<Course*> c;
};

In my .cpp file this is what I have:

#include <string>
#include <vector>
#include <iostream>
using namespace std;
string STUDENT = "dwilliams136";     // Add your name Blackboard/occ-email ID

#include "h26.h"

// Implement your code here
void print_student(Student* s)
{
	cout << "Student: " << s << endl;
}

void print_course(Course* c)
{
	cout << "Course Name: " << c << endl;
}

void enroll(Student* s, Course* c)
{
	Student *test;
	Course *test1;
	test = s;
	test1 = c;
}

I'm using Visual Studio 2013 and I can't get anything to compile. I'm not even sure what to do, any help would be appreciated. Thank you.

[Luke Leber]

Hi there, you will need to include the standard library headers for the artifacts that you're using in your header file. Otherwise the compiler will puke when it comes across a name that it can't find. You will also either have to (not recommended) put a 'using' declaration in your header or (recommended) explicitly qualify the artifacts that you're using from standard headers.

// Recommended
#ifndef HEADER_HPP
#define HEADER_HPP
#include <string>
class Student
{
    // using the class 'string' from the 'std' namespace
    std::string name;
};
#endif

// Not Recommended
#ifndef HEADER_HPP
#define HEADER_HPP
#include <string>
// this pollutes the ADL namespace list for anyone who includes your header file
// In fact, many compilers issue warnings for doing this!
using namespace std;
class Student
{
    string name;
};
#endif

Typically, a C++ interface / implementation pair are used in this fashion:

/* Interface.hpp */
class X
{
    /* declarations */
};

/* Implementation.cpp */
#include "Interface.hpp"

/* define the members of X */

The #include directive is essentially a glorified copy and paste. When #including a file, all that you are doing is telling the compiler to paste whatever is in the file in the spot that you've #included it. So in this case, you're pasting your header file at the top of your implementation file, then feeding the compiler the resulting 'translation unit' as it's called.

Another issue that I can see off-hand is in your printing functions, you're printing out the pointers that are provided.

// Implement your code here  
void print_student(Student* s)  
{  
    /// Prints out the value of whatever memory location that 's' resides in
    cout << "Student: " << s << endl;  

    /// Prints out the (std::string) member 'name'
    std::cout << "Student: " << s->name << std::endl;
}  
  
void print_course(Course* c)  
{  
    /// Prints out the value of whatever memory location that 'c' resides in
    cout << "Course Name: " << c << endl;  

    ///
    std::cout << "Course Name: " << c->name << std::endl;
}  
  
void enroll(Student* s, Course* c)  
{  
    // Perhaps what you want to do is:
    c->students.push_back(s);
    s->courses.push_back(c);
}  

This then of course makes memory management a bit tricky. There is a better way using *Modern C++* as illustrated below:

#ifndef INTERFACE_HPP
#define INTERFACE_HPP

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

class Student;

struct Course
{
    std::string name;
    std::vector<std::shared_ptr<Student>> students;
};

struct Student
{
    std::string name;
    std::vector<std::shared_ptr<Course>> courses;
};

void print_student(std::shared_ptr<Student> s)  
{  
    std::cout << "Student: " << s->name << std::endl;  
}  
  
void print_course(std::shared_ptr<Course> c)  
{  
    std::cout << "Course Name: " << c->name << std::endl;  
}  
  
void enroll(Student& student, Course& course)  
{
    student.courses.push_back(std::make_shared<Course>(course));
    course.students.push_back(std::make_shared<Student>(student));
} 

int main()
{
    Student alice { "alice" };
    Course math { "math" };
    Course english { "english"};

    enroll(alice, math);
    enroll(alice, english);
}

#endif

I'm sorry that your instructor is still teaching outdated C++. Bear with it until you pass the course, then explore the wonders of "modern" C++.

* Not quite sure why code tags aren't working.

[Campbell Ritchie]

Luke Leber wrote: . . .

* Not quite sure why code tags aren't working.

Because you wrote [code=C++11] and we don't have a C++ option?? They worked when I got rid of =C++11 and re‑enabled BB code.

That's a bl**d* good post, BTW.

[Kurt VanderKoi]

Subject: C++ pointers, Struct, and Vectors

Interesting code.

Something is missing. How do I print out:

- Student course information

-Course student information