c++ return private array

Question

hi, i've a class and there is an array set as private, how do i make the get_array() function i mean how do i return that array knowing that i will have to return a pointer of arr[0] as we know , but isn't this breaking the private rule ? is there other way of returning array ?

I actually thought of having array2 in the main , then edit that array using the class function. i think it will be a plan B if the above didn't work.

Answer 1

You cannot return an array from a function. You can, as you say, return a pointer to the first element of an array, but this has the downside that you have to have some separate functionality to obtain the size of the array from outside of the class.

A better option would be to return a struct that contains an array. The easiest way to do this would be to use the array class, which can be found in Boost and in many standard library implementations.

For example,

class C
{
public:
    typedef boost::array<int, 5> ArrayType;
    ArrayType get_array() const { return array_; }

private:
    ArrayType array_;
};

Answer 2

I would use std::vectors instead of arrays in C++. You can return them just like a primitive (vector<whatever> getter(){ return foo;}), and they tend to be easier to deal with.

Answer 3

Return a const reference to the array to make it read-only.

const ArrayType& ma = myClass->get_array();

Unless your clients are evil, they should not be able to modify the array. :-) For clarity, the class with the array and the array itself cannot go out of scope while you are using it.

Edited for typo.

Answer 4

From a pure OO perspective, it really depends who is going to use the private variable of your class. If it is a friend class, or another trusted entity, there is no problem in handing out the private data member.

Answer 5

You can do a few things.

The simplest is to return a pointer to the first element that is const: const int* get_array(void) const; You might want to make a function to query the size as well.

A better option might be to return a const-reference to the array. Use a typedef to make it simple:

typedef int array_type[10];
const array_type& get_array(void) const;

Another option is to wrap the array up, like boost::array. You can copy and paste Boost's header if you want, into your own array.hpp:

typedef boost::array<int, 10> array_type;
const array_type& get_array(void) const;