Getters and Setters with std::vector private members

[dariodem]

Hi People,

Please correct me if i am wrong.
From this code, and for my surprise, I realized that the getter member function returns the std::vector by value (by default).

// Example program
#include <iostream>
#include <vector>

using namespace std;

class C {
    private:
        std::vector<int>    v;
    
    public:
        C() {
            v.resize(10);
        }
        
        std::vector<int> getv() {
            return  v;
        }
        
        void    setv( std::vector<int> v1 ) {
            v = v1;
        }
};


int main()
{
    std::vector<int>    v2;
    C   myC;
    
    std::cout << "v content in myC is " << endl; 
    for(int d : myC.getv()) std::cout << d << ' ';
    std::cout << endl;

    v2 = myC.getv();

    std::cout << "after v2 = myC.getv(), v2 content is " << endl; 
    for(int d : v2) std::cout << d << ' ';
    std::cout << endl;

    v2[4] = 1;

    std::cout << "after v2[4] = 1;, v2 content is " << endl; 
    for(int d : v2) std::cout << d << ' ';
    std::cout << endl;

    std::cout << "but now, v content is " << endl; 
    for(int d : myC.getv()) std::cout << d << ' ';
    std::cout << endl;

    myC.setv(v2);

    std::cout << "after myC.setv(v2), v content is " << endl; 
    for(int d : myC.getv()) std::cout << d << ' ';
    std::cout << endl;

    std::cout << "and v2 content is " << endl; 
    for(int d : v2) std::cout << d << ' ';
    std::cout << endl;

    return  0;
}

My question is:

What is the right way to code getters and setters with these kind of data (std::vectors).
I don't want to enter in philosophical topics like the one exposed in:
http://www.cplusplus.com/forum/lounge/101305/
That is great!

Yet I just want to receive an answer in terms of the pros and cons about coding getters and setters in one way or another.

Thanks!

[jlb]

IMO your class makes no sense. You're doing all of the processing outside the class so there is really no need for the class, just use a non-class vector instance.

[dariodem]

Thanks jib.

Please, don't worry about the class. It is just an example. It is obvious that there is implicitly more stuff inside it.

[ne555]

> returns the std::vector by value (by default).
There is no «by default», you tell it to return a copy, it'll return a copy, you tell it to return a reference, it'll return a reference.

[dariodem]

Thanks ne555,

then: How do I tell it to return a reference?
Do I have to manage pointers for it? Or: Is there a different way for doing this with std::vector?

[ne555]

std::vector<int>& getv()

[dariodem]

Well,
Please, excuse me if I don't understand something obvious.

I followed your indication ne555, and the output in the program, is:

v content in myC is 
0 0 0 0 0 0 0 0 0 0 
after v2 = myC.getv(), v2 content is 
0 0 0 0 0 0 0 0 0 0 
after v2[4] = 1;, v2 content is 
0 0 0 0 1 0 0 0 0 0 
but now, v content is 
0 0 0 0 0 0 0 0 0 0 
after myC.setv(v2), v content is 
0 0 0 0 1 0 0 0 0 0 
and v2 content is 
0 0 0 0 1 0 0 0 0 0

after the modification of v2 (which is supposed to be a reference to v) by means of v2[4] = 1;
v content is
0 0 0 0 0 0 0 0 0 0
but v2 is
0 0 0 0 1 0 0 0 0 0

Again, excuse me if I am missing some obvious detail.

The "&" seems to make no effect in the code at all.

Thanks

[dariodem]

Finally I could see my mistake:

I have to declare v2 as reference.

// Example program
#include <iostream>
#include <vector>

using namespace std;

class C {
    private:
        std::vector<int>    v;
    
    public:
        C() {
            v.resize(10);
        }
        
        std::vector<int>& getv() {
            return  v;
        }
        
        void    setv( std::vector<int> v1 ) {
            v = v1;
        }
};


int main()
{
    C   myC;
    
    std::cout << "v content in myC is " << endl; 
    for(int d : myC.getv()) std::cout << d << ' ';
    std::cout << endl;

    std::vector<int>    &v2 = myC.getv();  // here is the modification

    std::cout << "after v2 = myC.getv(), v2 content is " << endl; 
    for(int d : v2) std::cout << d << ' ';
    std::cout << endl;

    v2[4] = 1;

    std::cout << "after v2[4] = 1;, v2 content is " << endl; 
    for(int d : v2) std::cout << d << ' ';
    std::cout << endl;

    std::cout << "but now, v content is " << endl; 
    for(int d : myC.getv()) std::cout << d << ' ';
    std::cout << endl;

    myC.setv(v2);

    std::cout << "after myC.setv(v2), v content is " << endl; 
    for(int d : myC.getv()) std::cout << d << ' ';
    std::cout << endl;

    std::cout << "and v2 content is " << endl; 
    for(int d : v2) std::cout << d << ' ';
    std::cout << endl;

    return  0;
}

Thanks for the comments