Syntax error, cant use struct in c++ class

Question

I am currently learning C++ and working on a assignment which asks me to create:

Class student (must be separated by .h and .cpp) that inherits class person that has:
a. Attributes: dynamic array of struct holding courses and their grades and other attributes
b. Member functions: display the grade of a given course and other member functions as as needed

So, to start, I have already created the class person; so don't worry about the inheritance nor classes, my only problem is with structs, here is my code:

student.h

#include <string>
#ifndef student_h
#define student_h
#include "person.h"
class student: public person {

private:
        struct stud {
            int age;
        };

public:
        student();
        int getAge();
};

#endif

student.cpp

#include <iostream>
#include <string>
using namespace std;
#include "student.h"


student::student() {


}

int student::getAge() {

    return stud.age;
}

So, my logic is, in the same way, that if you define a private integer in the .h file and use it freely in the .cpp file, I should do it for the struct. When I try to compile student.cpp for synthax error before running main.cpp, I get this error:

.\student.cpp(14) : error C2275: 'student::stud' : illegal use of this type as an expression

which is referring to return stud.age;. I am using (and forced to use) Visual Studio 2005.

How do I retrieve the age of the struct using a function? Also, what does my teacher mean by an array of structs? Does it mean I have to create the array in the main and how?

The nested class definition (the struct) is just that. It doesn't declare a data member of that type. By the way, the prefix get is just annoying verbiage in C++. You would not write getCos(x) for the cosine function, would you? Likewise, just age is fine to access or compute the age. Oh, and better store the birth year, not the age. Or else the data will get outdated fast. — Cheers and hth. - Alf
– Cheers and hth. - Alf, Commented Mar 9, 2016 at 19:07

Sergey Kalinichenko · Accepted Answer · 2016-03-09 19:12:34Z

3

Nested class stud defines a new type, not a variable of that type. If you wish to make a variable of type stud, declare a separate member for it, like this:

class student: public person {
private:
        struct stud_t {
            int age;
        };
        stud_t stud;
public:
        student();
        int getAge();
};

Now stud_t is the name of the type, and stud is the name of a variable of that type.

Alternatively, you could make stud an anonymous struct, like this:

class student: public person {
private:
        struct {
            int age;
        } stud;
public:
        student();
        int getAge();
};

answered Mar 9, 2016 at 19:12

Sergey Kalinichenko

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1 Comment

Joseph D Over a year ago

Thank you, my problem is solved and I understand now. You rock \m/

Reuben Thomas · Accepted Answer · 2016-03-09 19:15:15Z

2

If you really want to store stuff in an internal struct (I don't think you should) then you could write your struct like this:

struct {
    int age;
} stud;

In your example, you're declaring a struct of type stud but then not creating an instance. In the snippet above, I declare an anonymous struct (ie it's type has no name) and then create an instance called stud. Your current getAge should work if you make this change.

'dynamic array' == vector

answered Mar 9, 2016 at 19:15

Reuben Thomas

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