Vector max_size() in C++ STL

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

Last Updated : 14 May, 2023

In C++, Non-member buddy functions may access a class’s private members while not being members. The class definition declares them friend. Vector containers, dynamic arrays in C++ Standard Library (STL), may dynamically resize as members are added or deleted. You may need to establish a new class with a vector to utilize non-member friend methods on vector data.

Example:

C++

// 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; 
}

Output

Vector elements: 1 2 3 4 5

Explanation of the above program

In the above example, we have created a Vector Wrapper class that has a private vector named data. We have declared a non-member friend function printVector() that can access and print the vector data. This is just a simple example, and you can use a similar approach to create more complex friend functions to manipulate the vector data in the custom class.

Time Complexity: O(n)

Space difficulty: O(1)

Vector max_size() in C++ STL

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