Access modifiers

<h2 id="names-of-keywords">Names of keywords</h2>
<p>C++ uses the three modifiers called <i>public</i>, <i>protected</i>, and <i>private</i>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> <a href="/facts/C_Sharp_(programming_language)/UC2gxeyb">C#</a> has the modifiers <i>public</i>, <i>protected </i>,<i>internal</i>, <i>private</i>, <i>protected internal</i>, <i>private protected</i>, and <i>file</i>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a> has <i>public</i>, <i>package</i>, <i>protected</i>, and <i>private</i>; <i>package</i> is the default, used if no other access modifier keyword is specified. The meaning of these modifiers may differ from one language to another. A comparison of the keywords, ordered from the most restrictive to the most open, and their meaning in these three languages follows. Their visibility ranges from the same class to the package where the class is defined to a general access permission. Below, the maximal access is written into the table.
</p><p>In Swift, there are five different access levels relative to both the source file in which the entity is defined and the module containing that source file.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>
<table><tbody><tr><th>Keyword</th><th>C#</th><th>C++</th><th>Java</th><th>Swift</th></tr><tr><td>private</td><td>class</td><td>class<i>and/or</i><a href="/facts/Friend_class/IBte0WD0">friend classes</a></td><td>class</td><td>enclosing declaration only+ extensions of declaration in same file</td></tr><tr><td>fileprivate</td><td>-</td><td>-</td><td>-</td><td>same file</td></tr><tr><td>file</td><td>same file</td><td>-</td><td>-</td><td>-</td></tr><tr><td>private protected</td><td>derived classes in the same assembly</td><td>-</td><td>-</td><td>-</td></tr><tr><td>protected internal</td><td>same assembly<i>and/or</i>derived classes</td><td>-</td><td>-</td><td>-</td></tr><tr><td>protected</td><td>derived classes</td><td>derived classes<i>and/or</i>friend classes</td><td>derived classes<i>and/or</i>within same package</td><td>-</td></tr><tr><td>package</td><td>-</td><td>-</td><td>within its package</td><td>-</td></tr><tr><td>internal</td><td>same assembly</td><td>-</td><td>-</td><td>same module</td></tr><tr><td>public</td><td>everybody</td><td>everybody</td><td>everybody</td><td>everybody</td></tr><tr><td>open</td><td>-</td><td>-</td><td>-</td><td>everybody + subclass outside module+ override outside module</td></tr></tbody></table>
<h2 id="example-in-c">Example in C++</h2>
#include <iostream>
#include <conio.h>
using std::cout;
using std::endl;

struct B { // default access modifier inside struct is public
    void set_n(int v) { n = v; }
    void f()          { cout << "B::f" << endl; }
  protected:
    int m, n; // B::m, B::n are protected
  private:
    int x;
};
 
struct D : B {
    using B::m;               // D::m is public
    int get_n() { return n; } // B::n is accessible here, but not outside
//  int get_x() { return x; } // ERROR, B::x is inaccessible here
 private:
    using B::f;               // D::f is private
};
 
int main() {
    D d;

//  d.x = 2; // ERROR, private
//  d.n = 2; // ERROR, protected
    d.m = 2; // protected B::m is accessible as D::m

d.set_n(2); // calls B::set_n(int)
    cout << d.get_n() << endl; // output: 2

//  d.f();   // ERROR, B::f is inaccessible as D::f

B& b = d; // b references d and "views" it as being type B

//  b.x = 3; // ERROR, private
//  b.n = 3; // ERROR, protected
//  b.m = 3; // ERROR, B::m is protected

b.set_n(3); // calls B::set_n(int)
//  cout << b.get_n(); // ERROR, 'struct B' has no member named 'get_n'

b.f();   // calls B::f()
    return 0;
}

<h3>Notes</h3>

<h3>Bibliography</h3>
<ul><li>Mayo, Joseph (2002), <a href="https://books.google.com/books?id=XdHYaE-Il9gC"><i>C Sharp Unleashed</i></a>, Sams publishing, <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9780672321221</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Mayo 2002, pp. 199. - Mayo, Joseph (2002), C Sharp Unleashed, Sams publishing, ISBN 9780672321221 <a href="https://books.google.com/books?id=XdHYaE-Il9gC" target="_blank">https://books.google.com/books?id=XdHYaE-Il9gC</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Wagner, Bill. "Access Modifiers - C# Programming Guide". docs.microsoft.com. Retrieved 2020-01-13. <a href="/wiki/Bill_Wagner_(software)" target="_blank">/wiki/Bill_Wagner_(software)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"Access specifiers". en.cppreference.com. Retrieved 2020-01-13. <a href="https://en.cppreference.com/w/cpp/language/access" target="_blank">https://en.cppreference.com/w/cpp/language/access</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Access Modifiers (C# Reference)". learn.microsoft.com. Microsoft. 2022-09-27. Retrieved 2023-02-08. <a href="https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/access-modifiers" target="_blank">https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/access-modifiers</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"Access Control — The Swift Programming Language (Swift 5.3)". docs.swift.org. Retrieved 2021-02-08. <a href="https://docs.swift.org/swift-book/LanguageGuide/AccessControl.html" target="_blank">https://docs.swift.org/swift-book/LanguageGuide/AccessControl.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
</ol>

Access modifiers open-in-new

Access modifiers