Function undeclared(first use this function)

Question

i'm working on Matrix class,but i cant figure it out why i get this error since i already defined problematic function(Dopisi()).This is what i have so far:

This is what i have so far:

#include<IOStream>
using namespace std;

class Matrica{

private:int Duzina;
    int Sirina;
    int** pok;

public:
    Matrica(){//default constructor
        Duzina=0;
        Sirina=0;
        int i,j;
        pok=new int* [Duzina];
        for(i=0;i<Duzina;i++){
            pok[i]=new int[Sirina];

        }
    }
    Matrica(int duz,int sir){//constructor
        Duzina=duz;
        Sirina=sir;
        int i,j;
        pok=new int* [Duzina];
        for(i=0;i<Duzina;i++){
            pok[i]=new int[Sirina];
            for(j=0;j<Sirina;j++){
                pok[i][j]=0;
            }
        }
    }
    void Dodaj(int i,int j){//add one element
        cout<<"Unesite element ["<<i<<"]["<<j<<"]"<<endl;
        cin>>pok[i][j];
    }
    void Popuni(){//fill entire matrix
        int i,j;
        for(i=0;i<Duzina;i++)
            for(j=0;j<Sirina;j++)
                Dodaj(i,j);
    }
    Matrica(Matrica& mat){//copy constructor
        Duzina=mat.Duzina;
        Sirina=mat.Sirina;
        int i,j;
        pok=new int* [Duzina];
        for(i=0;i<Duzina;i++){
            pok[i]=new int[Sirina];
            for(j=0;j<Sirina;j++){
                pok[i][j]=mat.pok[i][j];
            }
        }
    }
    ~Matrica(){}
    int max(int a,int b){//max value
        if(a>b)return a;
        else
            return b;
    }
    void Ispis(){//cout
        int i,j;
        for(i=0;i<Duzina;i++){
            for(j=0;j<Sirina;j++){
                cout<<pok[i][j]<<" ";
            }
            cout<<endl;
        }
    }
    Matrica& operator =(const Matrica& x){
        for(int i=0;i<Duzina;i++)
            delete pok[i];

        Duzina=x.Duzina;
        Sirina=x.Sirina;
        for(int i=0;i<Duzina;i++){
            for(int j=0;j<Sirina;j++){
                pok[i][j]=x.pok[i][j];
            }
        }
        return *this; 
    }
    Matrica Dopisi(const Matrica a,const Matrica b);
};
Matrica Matrica::Dopisi(const Matrica a,const Matrica b){//function must take two      matrices 
    int i,j,duz,sir;
    duz=max(a.Duzina,b.Duzina);
    sir=a.Sirina+b.Sirina;
    Matrica temp(duz,sir);
    for(i=0;i<a.Duzina;i++){
        for(j=0;j<a.Sirina;j++){
            temp.pok[i][j]=a.pok[i][j];
        }
    }
    for(i=0;i<b.Duzina;i++){
        for(j=0;j<b.Sirina;j++){
            temp.pok[i][j+a.Sirina]=b.pok[i][j];
        }
    }
    temp.Ispis();
    // return temp;
}
int main(){
    Matrica mat1(3,3);
    mat1.Popuni();
    mat1.Ispis();
    Matrica mat2(4,4);
    mat2.Popuni();
    mat2.Ispis();
    mat2=mat1;
    mat2.Ispis();
    Matrica mat3;
    mat3=Dopisi(mat1,mat2);
    system("pause");
    return 0;
}

P.S.Names of variables and methods are in Serbian,hope you'll figure it out.Thanks in advance

Answer 1

Dopisi is a member function in the Matrica class. If you want it to be a free-standing function it should be declared or defined outside the class.

If you want it to be able to access private member, then declare it as a friend function, or make it a static member function (but then you have to call it as Matrica::Dopisi(...)).

Answer 2

Besides the problem with the function the class definition is invalid. First of all the destructor does not release memory pointed by pok. Also the assignment operator is incorrect.

Matrica& operator =(const Matrica& x){
    for(int i=0;i<Duzina;i++)
        delete pok[i];

    Duzina=x.Duzina;
    Sirina=x.Sirina;
    for(int i=0;i<Duzina;i++){
        for(int j=0;j<Sirina;j++){
            pok[i][j]=x.pok[i][j];
        }
    }
    return *this; 
}

First of all instead of delete pok[i]; shall be delete []pok[i]; Also you did not release used memory and allocate a new memory according to new values of Duzina and Sirina.

So the operator function has undefined behavior and without doubts its work will result in program exception.

Answer 3

Make the function

public:
static Matrica Dopisi(const Matrica &a,const Matrica &b);

Then you can call it outside the class as

mat3 = Matrica::Dopisi(mat1,mat2);

without needing an instance of the class

Answer 4

You declare Dopisi function as a class method (put it inside your class declaration), but then you call it as a global function. For example, it could be called as mat3.Dopisi(mat1, mat2).

In your case, Dopisi needs to have access to Matrica class, so just make it a friend-function:

...

// in class declaration:
friend Matrica Dopisi(const Matrica a,const Matrica b);

...

// in function definition:
Matrica Dopisi(const Matrica a,const Matrica b){//function must take two      matrices

...

// leave your function call as it is

Answer 5

You are calling Dopisi as if it were a regular function. It is a member function and so needs to be called on an instance of class Matrica. The actual style of this function would indicate that it would be better as a non-member function as calling this function as currently, it requires an instance of Matrica to call on but also takes 2 instances of Matrica as arguments and also returns a fourth. Thus you have 4 instances in total. It seems more appropriate to use a nonmember function taking t instances of Matrica and returning the result.

This would of course also require getter/setter functions for the private members of the class that are accessed within that function.