从具有引用返回类型的函数返回什么？

Question

className &temp (someOtherclassName &c)

The question is what should I return I am trying to return just an object that is newly created in the class, it's not working, I also tried returning reference or pointer, and it's not working.

Klub &novKlub(Clen &c){
    Klub newKlub;
    strcpy(newKlub.name, name);

    for(int i = 0; i < elements; i++){
        if(c.getLevel() == clenovi->getLevel()){
            newKlub += clenovi[i];

        }

    }
    return newKlub;
}

---

Here's all the code:

#include<iostream>
#include<cstring>
using namespace std;
class Clen{
private:
char name[50];
char surname[50];
int level;
public:
Clen(char n[] = "null", char s[] = "null", int l = 1){
    strcpy(name, n);
    strcpy(surname, s);
    level = l;
}

//operator++
Clen operator++(int){
    Clen temp(*this);
    ++level;
    return temp;
}

//++operator
Clen &operator ++ (){
    ++level;

    return *this;
}

int getLevel(){
    return level;
}

//operator <<
friend ostream &operator << (ostream &output, const Clen &right);

//operator==
friend bool operator == (const Clen &left, const Clen &right);

//operator!=
friend bool operator != (const Clen &left, const Clen &right);

};
ostream &operator << (ostream &output, const Clen &right){
output << right.name << " " << right.surname << ", " << right.level << endl;
return output;
}

bool operator == (const Clen &left, const Clen &right){
if(left.level == right.level)
    return true;

return false;
}

bool operator != (const Clen &left, const Clen &right){
return !(left == right);
}

class Klub{
private:
char name[100];
Clen *clenovi;
int elements;
void copy(const Klub &toCopy){
    strcpy(name, toCopy.name);
    elements = toCopy.elements;

    clenovi = new Clen[elements + 1];
    for(int i = 0; i < elements; i++){
        clenovi[i] = toCopy.clenovi[i];
    }
}

public:
//constructor
Klub(char n[] = "null", Clen c[] = NULL, int e = 0){
    strcpy(name, n);
    elements = e;

    clenovi = new Clen[elements + 1];
    for(int i = 0; i < elements; i++){
        clenovi[i] = c[i];
    }
}
//copy constructor
Klub(const Klub &toCopy){
    copy(toCopy);
}

//assignment operator
Klub &operator = (const Klub &right){
    if(this == &right)
        return *this;
    delete [] clenovi;
    copy(right);

    return *this;
}

//destructor
~Klub(){
    delete [] clenovi;
}

//operator <<
friend ostream &operator << (ostream &output, const Klub &right);


//operator +=
Klub &operator +=(Clen c){
    Clen *temp = clenovi;
    clenovi = new Clen[elements + 1];

    for(int i = 0; i < elements; i++){
        clenovi[i] = temp[i];

    }

    clenovi[elements] = c;
    ++elements;
    delete [] temp;
    return *this;

}

Klub &novKlub(Clen &c){
    Klub newKlub;
    strcpy(newKlub.name, name);

    for(int i = 0; i < elements; i++){
        if(c.getLevel() == clenovi->getLevel()){
            newKlub += clenovi[i];

        }

    }
    return *this;
}
};

ostream &operator << (ostream &output, const Klub &right){
output << right.name << endl;
for(int i = 0; i < right.elements; i++){
    output << right.clenovi[i] << endl;
}

return output;
}
int main()
{
Clen clen;
int n, stepen;
char ime[30], prezime[30];
cin >> ime >> n;
Klub k1(ime); 
for(int i = 0; i < n; i++){
    cin >> ime >> prezime >> stepen;
    Clen c(ime, prezime, stepen);
    k1 += c;
    clen = c; 
}  
Klub k2 = k1.novKlub(clen);
cout << k2;
return 0;
}

Answer 1

You should return your object by value, not reference. Change your declaration to:

Klub novKlub(Clen &c)

Functions should never return a reference to a local object, as it is destroyed upon function return leaving a dangling reference.

UPDATE: If changing the signature is not an option, you should still not return a reference to a local. In this case, presumably the intention is to create the object which is inserted into some container, and then return a reference to it within this container. You haven't provided enough detail about your classes to say exactly what this could be, but perhaps it shoud be inserted into clenovi or c . If you provide more detail for those this can be clarified.

Answer 2

Given that you are creating a new object, return it by value.

Situations that call for returning a reference are somewhat limited (see below). Your situation is not one of them.

The question is what should I return [if I want to return a reference]

You should return an object with static lifetime, or lifetime known to the caller. Make sure that the caller does not need to free your object.

I am trying to return just an object that is newly created in the class, it's not working

You should not require the caller to free objects that you return by reference, so returning a newly created object is not an option.

I also tried returning reference or pointer, and it's not working.

You need to return an object that does not go out of scope upon return. Usually you want to return

• Your object itself, ie *this , or
• One of your object's dependents, ie this->someField , or
• One of your function parameters (this is a very common pattern in << overriding), or
• A static or global variable (not recommended).