Default Access Specifiers in C : Clarifying Private and Public by Default

In the C programming language, understanding the default access specifiers is crucial when defining classes and structures. The keywords private, public, and protected are used to specify the visibility and accessibility of class members. This article aims to provide a comprehensive guide to the default access specifiers, particularly in the context of class and struct definitions in C .

Overview of Access Specifiers

C supports three primary access specifiers: public, private, and protected. These keywords determine the visibility and accessibility of class members from outside the class.

Default Access Specifiers for Class Members

When a class or structure is defined, the default access specifier for its members is different depending on the keyword used: class or struct.

In the case of a class, if no access specifier is explicitly provided, the default is private. This means that if you do not specify public or protected for a member, it is considered private by default. For example:

class TrivialClass {private:    int x; // Private memberpublic:    int getWidth(); // Public member};

Similarly, in the case of a struct, the default access specifier is public. If no access specifier is provided, the members are considered public by default. For example:

struct TrivialStruct {public:    int getWidth(); // Public memberprivate:    int x; // Private member};

These definitions ensure that the members with no explicit access specifier are accessible from outside the class if it is a struct, and are not accessible if it is a class.

Default Access Specifiers in Inheritance

Besides class and struct definitions, the default access specifier also applies to inheritance. When a class inherits from another class or struct, the default access specifier for the inherited members is determined by the base class's default access specifier.

In private inheritance, the inherited members from the base class are considered private. If you do not specify a different access specifier, the base class members are treated as part of the derived class's private members. For example:

class Base {public:    int a;private:    int b;};class Derived : private Base {public:    // Base::a is treated as private in Derived    // Base::b is treated as private in Derived};

On the other hand, in public inheritance, the inherited members from the base class are considered public. If you do not specify a different access specifier, the base class members are treated as part of the derived class's public members. For example:

class Base {public:    int a;private:    int b;};class Derived : public Base {public:    // Base::a is treated as public in Derived    // Base::b is treated as public in Derived};

Best Practices and Explicitness

Most developers prefer to make their intentions explicit by using the appropriate access specifiers. This practice enhances the readability and maintainability of the code. By explicitly stating whether a member should be public, private, or protected, you avoid potential misunderstandings and errors.

For example:

class ExplicitTrivialClass {private:    int x;public:    int getWidth();};

While it is not strictly necessary to use the private keyword, doing so clearly communicates your intent to other developers or yourself in the future.

Conclusion

Understanding the default access specifiers in C is essential for effective class and structure design. The default private for classes and public for structs ensures encapsulation and proper compartmentalization of code. However, making your intentions explicit through the use of access specifiers is a best practice that promotes better code quality and maintainability.

Frequently Asked Questions

Q: In C , what is the default access specifier for class members?
A: The default access specifier for class members is private. Q: Do I need to use the private, public, and protected keywords?
A: While it is not strictly necessary to use these keywords for members with a default access specifier, it is recommended to make your intentions explicit for clarity and maintainability. Q: How does inheritance affect access specifiers?
A: Inheritance affects the visibility of base class members. By default, private inheritance makes the base class members private in the derived class, and public inheritance makes them public.

By carefully considering and using access specifiers, you can enhance the clarity and functionality of your C code.