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Names of keywords

C++ uses the three modifiers called public, protected, and private.³ C# has the modifiers public, protected ,internal, private, protected internal, private protected, and file.⁴ Java has public, package, protected, and private; package 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.

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.⁵

Keyword	C#	C++	Java	Swift
private	class	classand/orfriend classes	class	enclosing declaration only+ extensions of declaration in same file
fileprivate	-	-	-	same file
file	same file	-	-	-
private protected	derived classes in the same assembly	-	-	-
protected internal	same assemblyand/orderived classes	-	-	-
protected	derived classes	derived classesand/orfriend classes	derived classesand/orwithin same package	-
package	-	-	within its package	-
internal	same assembly	-	-	same module
public	everybody	everybody	everybody	everybody
open	-	-	-	everybody + subclass outside module+ override outside module

Example in C++

#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; }

Notes

Bibliography

• Mayo, Joseph (2002), C Sharp Unleashed, Sams publishing, ISBN 9780672321221

References

1. Mayo 2002, pp. 199. - Mayo, Joseph (2002), C Sharp Unleashed, Sams publishing, ISBN 9780672321221 https://books.google.com/books?id=XdHYaE-Il9gC ↩

2. Wagner, Bill. "Access Modifiers - C# Programming Guide". docs.microsoft.com. Retrieved 2020-01-13. /wiki/Bill_Wagner_(software) ↩

3. "Access specifiers". en.cppreference.com. Retrieved 2020-01-13. https://en.cppreference.com/w/cpp/language/access ↩

4. "Access Modifiers (C# Reference)". learn.microsoft.com. Microsoft. 2022-09-27. Retrieved 2023-02-08. https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/access-modifiers ↩

5. "Access Control — The Swift Programming Language (Swift 5.3)". docs.swift.org. Retrieved 2021-02-08. https://docs.swift.org/swift-book/LanguageGuide/AccessControl.html ↩