Multiple Definition Error with Operator[] ??

[bounddyy]

So i'm messing around with the operator[] since prof wasn't very clear on it but I get a build error for multiple definitions. I code mainly on cLion, I tested it on the latest Eclipse too same error. TO BE CLEAR! I get this error only when the function def is outside with the prototype inside the class, so if I define the function inside the class I don't get the error. My class code is as follows.

#ifndef UNTITLEDSCHOOOL_MYCLASS_H
#define UNTITLEDSCHOOOL_MYCLASS_H

#include <iostream>

using namespace std;


int const SIZE = 10;

class myClass {

private:

    int values[SIZE];
    int dummy;

public:

    myClass() {

        for (int i = 0; i < SIZE; i++) {
            values[i] = 0;
        }
        dummy = 0;

    }


    int operator[](int index) const {

        if (index < 0 || index >= SIZE) {

            return 0;
        }

        return values[index]; // returns the requested value;

    } // end of getter Operator; // getter

    int &operator[](int index) {

        if (index < 0) {

            return dummy;

        } else if (index >= 10) {
            return dummy;

        } else {
            return values[index];
        }
    }
};

#endif //UNTITLEDSCHOOOL_MYCLASS_H

[JLBorges]

> I get this error only when the function def is outside with the prototype inside the class,
> so if I define the function inside the class I don't get the error.

When the function definition is outside the class, make sure that you have not omitted the const qualifier.
int myClass::operator[](int index) const { ...

[andywestken]

If you define myClass::operator[] outside the class body in a header file and then include that header in two or more source files then you will get a Multiple Definition Error if you have forgotten to mark the method as inline. That is:

#ifndef UNTITLEDSCHOOOL_MYCLASS_H
#define UNTITLEDSCHOOOL_MYCLASS_H

#include <iostream>

using namespace std; // NOTE very bad practice to use using in a header!
// Esp when it's not even needed!?

int const SIZE = 10;

class myClass {
private:
    int values[SIZE];
    int dummy;

public:
    myClass() {
        for (int i = 0; i < SIZE; i++) {
            values[i] = 0;
        }
        dummy = 0;
    }

    int operator[](int index) const;
    int &operator[](int index);
};

inline int myClass::operator[](int index) const {
    if (index < 0 || index >= SIZE) {
        return 0;
    }
    return values[index]; // returns the requested value;
} // end of getter Operator; // getter

inline int &myClass::operator[](int index) {
    if (index < 0) {
        return dummy;
    } else if (index >= 10) {
        return dummy;
    } else {
        return values[index];
    }
}

#endif //UNTITLEDSCHOOOL_MYCLASS_H 

Alternatively define the functions in a single cpp file (but inline is better in the case, as the methods are tiny.)

Andy

PS methods defined within the class body are implicitly inline.