How to return a class object by reference in C++?

Question

I have a class called Object which stores some data.

I would like to return it by reference using a function like this:

    Object& return_Object         


        

Answer 1

I will show you some examples:

First example, do not return local scope object, for example:

const string &dontDoThis(const string &s)
{
    string local = s;
    return local;
}

You can't return local by reference, because local is destroyed at the end of the body of dontDoThis.

Second example, you can return by reference:

const string &shorterString(const string &s1, const string &s2)
{
    return (s1.size() < s2.size()) ? s1 : s2;
}

Here, you can return by reference both s1 and s2 because they were defined before shorterString was called.

Third example:

char &get_val(string &str, string::size_type ix)
{
    return str[ix];
}

usage code as below:

string s("123456");
cout << s << endl;
char &ch = get_val(s, 0); 
ch = 'A';
cout << s << endl; // A23456

get_val can return elements of s by reference because s still exists after the call.

Fourth example

class Student
{
public:
    string m_name;
    int age;    

    string &getName();
};

string &Student::getName()
{
    // you can return by reference
    return m_name;
}

string& Test(Student &student)
{
    // we can return `m_name` by reference here because `student` still exists after the call
    return stu.m_name;
}

usage example:

Student student;
student.m_name = 'jack';
string name = student.getName();
// or
string name2 = Test(student);

Fifth example:

class String
{
private:
    char *str_;

public:
    String &operator=(const String &str);
};

String &String::operator=(const String &str)
{
    if (this == &str)
    {
        return *this;
    }
    delete [] str_;
    int length = strlen(str.str_);
    str_ = new char[length + 1];
    strcpy(str_, str.str_);
    return *this;
}

You could then use the operator= above like this:

String a;
String b;
String c = b = a;