Cannot call member function without object but I call the function with an object

Question

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

class Human
{
private:
    string Name;
    int Age;
    friend class Utility;
public:
    Human(string InputName,int InputAge)
    {
        Name = InputName;
        Age = InputAge;
    }
};
class Utility
{
public:
    void DisplayAge(const Human& Person)
    {
        cout<<Person.Age<<endl;
    }
};
int main()
{
    Human FirstMan("Adam",25);
    cout<<"Accessing private member Age via friend class: ";
    Utility::DisplayAge(FirstMan);
}

I don't understand..when I call the function I do send an object(FistMan)..why my compiler still says that I call it without object?

Make it static. Then it will work. static void DisplayAge(const Human& Person). In utility class, all functions are static in most cases :) — unalignedmemoryaccess
– unalignedmemoryaccess, Commented Oct 13, 2017 at 13:16
You are not calling the function with an object. The class name is not an object. Create an object first: Utility myutility; then call its functions: myutility.DisplayAge(FirstMan);. — Galik
– Galik, Commented Oct 13, 2017 at 13:20

Bathsheba · Accepted Answer · 2017-10-13 13:16:50Z

6

DisplayAge in Utility is not a static function. Therefore you need an instance of Uitility in order to call it.

So, either make the function static, or call it via an anonymous temporary

Utility().DisplayAge(FirstMan);

Better still, make DisplayAge a member function of Human.

answered Oct 13, 2017 at 13:16

Bathsheba

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Comments

rak007 · Accepted Answer · 2017-10-13 13:32:55Z

1

Use the static keyword and then you'll be able to call your function on your class

I edited your code below :

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

class Human
{
private:
    string Name;
    int Age;
    friend class Utility;
public:
    Human(string InputName,int InputAge)
    {
        Name = InputName;
        Age = InputAge;
    }
};

class Utility
{
friend class Human;
public:
    Utility() = default;
    static void DisplayAge(const Human& Person)
    {
        cout<<Person.Age<<endl;
    }
};

int main(void)
{
    Human FirstMan("Adam",25);
    cout<<"Accessing private member Age via friend class: ";
    Utility::DisplayAge(FirstMan);
}

edited Oct 13, 2017 at 13:32

answered Oct 13, 2017 at 13:18

rak007

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1 Comment

rak007 Over a year ago

I wouldn't use my answer though as it is bad practice in general. Use the one from @Bathsheba

user2672107 · Accepted Answer · 2017-10-13 13:28:51Z

0

Dön't use a class whenever you want to define functions. Use a namespace:

namespace Utility
{
    inline void DisplayAge(const Human& Person)
    {
        cout<<Person.Age<<endl;
    }
}

int main()
{
    Human FirstMan("Adam",25);
    cout<<"Accessing private member Age via friend class: ";
    Utility::DisplayAge(FirstMan);
}

answered Oct 13, 2017 at 13:28

user2672107

2 Comments

NathanOliver Over a year ago

Age is private and can't be accessed without making more changes.

Bathsheba Over a year ago

But you can't friend a namespace; that's important here.

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