Using Non-Member Friend Functions With Vector in C++ STL

// C++ Program to use a non-member friend function with a
// custom VectorWrapper class that contains a vector from
// the C++ STL:
#include <iostream>
#include <vector>

// Custom class containing a vector
class VectorWrapper {
private:
    std::vector<int> data;

public:
    // Constructor
    VectorWrapper(const std::vector<int>& initialValues)
        : data(initialValues)
    {
    }

    // Declare a non-member friend function
    friend void printVector(const VectorWrapper& vw);
};

// Non-member friend function that has access to
// VectorWrapper's private members
void printVector(const VectorWrapper& vw)
{
    std::cout << "Vector elements: ";
    for (int value : vw.data) {
        std::cout << value << " ";
    }
    std::cout << std::endl;
}

int main()
{
    std::vector<int> initialValues = { 1, 2, 3, 4, 5 };
    VectorWrapper vw(initialValues);
    // Prints "Vector elements: 1 2 3 4 5"
    printVector(vw);

    return 0;
}