How use value of variable in another class

Question

Imagine I have a class and it has a private value for example this value name is a, then I set it's value to 10.

How I can access to this variable with its value (10) in another class?

(I do not want to use friend function and friend class)

a.h

#include <iostream>
using namespace std;
static int s=0;

/* run this program using the console pauser or add your own getch, system("pause") or input loop */

class a
{
    private:
    public:
        void sets(int );
};

a.cpp

#include "a.h"

void a::sets(int y){
    cin >> y;
    s=y;
}

main.cpp

#include"a.h"

int main()
{
    int i=0;
    int q;
    a a1;
    a1.sets(q);
    cout << s+1 << endl;
    for (i=1; i<5; i++){
        if (s == i) cout << "ok";
    }
}

An answer to this question can be found in any book/tutorial dealing with C++ classes. Please take the time to go through such a book. That will be more helpful for you in the long run than getting an answer to this specific question. — R Sahu, Apr 11 '17 at 18:52
Why you use a static global variable (`s`) instead of a private member? — Rama, Apr 11 '17 at 18:56
And the reason for that is every time a.h is included another `s` is defined. The linker doesn't know which which `s` is the real `s`, so it stops and complains. `static` makes a different `s` in every [translation unit](http://stackoverflow.com/questions/1106149/what-is-a-translation-unit-in-c) so the linker stops complaining, but now you have different `s`s. To do this right, and you don't need this here, Rama's answer is a better solution, you need to declare `extern int s;` in the header and in one and only one cpp file `int s;` to allocate storage for the single `s`. — user4581301, Apr 11 '17 at 19:55
[When to use extern in C++](http://stackoverflow.com/questions/10422034/when-to-use-extern-in-c) — user4581301, Apr 11 '17 at 19:56

score 0 · Answer 1 · answered Apr 11 '17 at 18:52

0

If you do not want to use friendship, add a public interface to this variable (setter and/or getter class members).

answered Apr 11 '17 at 18:52

bipll

11,747
1
18
32

its not suitable for me i have same problem – keyvan Apr 11 '17 at 19:01

Jesper Juhl · Answer 2 · 2017-04-11T19:10:02.277

0

Either make the variable public or add a function to get the value that returns it, like int getA() const { return a; } .

edited Apr 11 '17 at 19:10

answered Apr 11 '17 at 18:53

Jesper Juhl

30,449
3
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ok i know that , you just print its value i want add this with another value or use it in main – keyvan Apr 11 '17 at 18:55
Proper form would be int GetA() const; – Christopher Pisz Apr 11 '17 at 19:00
you just print s value i want work with this value and change it to main – keyvan Apr 11 '17 at 19:02

Rama · Answer 3 · 2017-04-11T19:26:17.143

Use a private member s in your class a instead of a global variable, and access it via public Getter function GetS

Example:

#include <iostream>
using namespace std;

class a
{
    private:
        int s;

    public:
        void SetS() { cin >> s; }
        int GetS() const { return s; } 
};

int main()
{
    a a1;
    a1.SetS();
    int s1=a1.GetS();
    cout << s1+1 << endl;
    for (int i=1; i<5; i++){
            if (s1 == i) cout << "ok";
    }
}

How use value of variable in another class

3 Answers3