When and Why Should You Use \'Default\' in C Class Function Declarations?

The Meaning of "Default" in Class Function Declarations

In C , the keyword "default" is commonly encountered in conjunction with class function declarations. It plays a crucial role in specifying the implementation of certain special functions, such as constructors, copy constructors, and assignment operators.

Understanding the "default" Keyword

The "default" keyword instructs the compiler to generate a default implementation for the specified function. This means that the compiler will automatically provide the code for the function, eliminating the need for manual implementation. By using "default," you signify your intention to utilize the standard definition of the function as defined by the compiler.

Examining the Provided Example

Consider the following class definition:

<code class="cpp">class C {
  C(const C&) = default;
  C(C&&) = default;
  C& operator=(const C&) & = default;
  C& operator=(C&&) & = default;
  virtual ~C() { }
};</code>

In this class, "default" has been used next to the copy constructor, the move constructor, the copy assignment operator, and the move assignment operator. This indicates that the compiler should generate default implementations for all these functions.

Advantages of Using "default"

Using "default" offers several benefits:

• Simplicity: It simplifies code by eliminating the need to explicitly define common patterns.
• Consistency: It ensures consistency in the implementation of special functions, reducing the chance of errors.
• Flexibility: It allows you to specify whether you want the compiler to generate a function or not (using "default" or "= delete", respectively).

Conclusion

The "default" keyword in class function declarations is a valuable tool that allows you to control the implementation of special functions. By utilizing "default," you instruct the compiler to generate a standard implementation, keeping your code concise and consistent. Conversely, you can use "= delete" to prevent the compiler from generating a function automatically, giving you complete control over its implementation.

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