In the overload of, it says that there is an initializer error before &

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In the overload of, it says that there is an initializer error before &

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#1 by (2 votes)

1

#include <iostream>
#include <cstdlib>

using namespace std;

class vector {

    private: int *pv, tam;

    public: vector (int *a, int tam){
        pv= new int [tam];
        for (int i=0; i<tam; i++){
            pv[i]=a[i];
        }
    }
    vector operator + (vector b);
    friend ostream& operator << (ostream &o, vector b);
}

////
ostream & operator << (ostream &o, vector b){
    for (int i=o; int i<b.tam; i++){
    o<<b.pv[i]<<endl;
    return o;
    }
}
////
vector::operator + (vector b){
    int tamanio= this->tam+b.tam;
    vector aux(0,0);
    aux.pv= new int [tamanio];

    for (int i=0; i<this->tam; i++){
        aux.pv[i]=this->pv[i];
    }
    for (int j=this->tam; j<tamanio; j++){
        aux.pv[j]=b.pv[j];
    }
    aux.tam=tamanio;
    return aux;
}



int main(int argc, char *argv[]) {
    int v1[3]; int v2[3];

    for (int i=0;i<3; i++){
        v1[i]=i++;
        v2[i]=i++;
    }
    vector v(v1, 3); vector vv(v2,3); vector res(v1,0);
    res=v+vv;
    cout<<res;
    return 0;
}

c++ poo

asked by Ale 11.08.2018 в 21:17

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1 answer

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score 2 · Answer 1

Your code has the following errors:

The vector constructor does not assign the value of the attribute tam .
Within the implementation of ostream you are assigning the ostream to the variable i that serves to iterate: for (int i=o .
You are returned the ostream in the first iteration of for , you must do it after iterating it completely.
In the expression: vector operator + (vector b); you are indicating that you must return a new object vector but your implementation does not: vector::operator + (vector b){ , the correct thing is vector vector::operator + (vector b){ .
In the following lines: for (int j=this->tam; j<tamanio; j++){ aux.pv[j]=b.pv[j]; ... j starts at position this->tam but you are using it as index in b.pv[j] , which will generate access to non-reserved memory position.
The variable used to iterate in a loop for which is used as indexes in the arrays should not be modified, in which case there are the following lines: v1[i]=i++; v2[i]=i++; , why is it wrong? , because the index is varying, for example we see the initial case: v1[i]=i++; i = 0, i++ is 1 and therefore equals v1[1] = 1 ; and then v2[i] = i++ would equal to v2[2] = 2; and in the next iteration v1[4] = 4 , and we are already in dangerous terrain since we have not reserved that memory.
If you want to assign a null pointer: vector aux(0,0); it is recommended to use nullptr .

Correcting the above we obtain the following code:

main.cpp

#include <iostream>

class vector {
    int *pv;
    int tam;
public:
    vector (int *a, int tam):
        pv(new int(tam)),
        tam(tam)
    {
        for (int i=0; i<tam; i++){
            pv[i]=a[i];
        }
    }
    vector operator + (const vector & b);
    friend std::ostream& operator << (std::ostream &o, const vector & b);
};

std::ostream & operator << (std::ostream &o, const vector & b){
    for (int i= 0; i< b.tam; i++){
        o << b.pv[i] << "\n";
    }
    return o;
}

vector vector::operator+(const vector & b){
    int tamanio = this->tam+b.tam;
    vector aux(nullptr, 0);
    aux.pv= new int[tamanio];
    for (int i=0; i<this->tam; i++){
        aux.pv[i]=this->pv[i];
    }
    for (int j = 0; j< b.tam; j++){
        aux.pv[j+this->tam] = b.pv[j];
    }
    aux.tam=tamanio;
    return aux;
}

int main(int argc, char *argv[]) {
    int v1[3];
    int v2[3];

    for (int i=0;i<3; i++){
        v1[i]=i+1;
        v2[i]=i+2;
    }
    vector v(v1, 3);
    vector vv(v2, 3);
    vector res(v1, 0);
    res = v + vv;
    std::cout <<"v:\n";
    std::cout<< v;
    std::cout << "vv:\n";
    std::cout<< vv;
    std::cout << "res:\n";
    std::cout<< res;
    return 0;
}

Exit:

v:
1
2
3
vv:
2
3
4
res:
1
2
3
2
3
4