Header vs. Implementation Files: Where Does My Code Belong?

Separating Code into Headers and Implementation Files

In software development, it's often necessary to divide code into multiple files to improve organization and maintainability. When using this approach, understanding what should be included in header (.h) files and implementation (.cpp) files becomes crucial.

Header Files (.h): Definitions

Header files are designed to contain definitions that will be shared across multiple files. These definitions include:

• Class declarations: Outline the structure and interface of classes.
• Function prototypes: Specify the signature of functions, including their name, return type, and argument types.
• Enumerations: Define symbolic representations for a set of related values.

Essentially, header files provide the necessary information for other files to utilize defined elements in the compilation process.

Implementation Files (.cpp): Implementations

Implementation files, on the other hand, contain the actual code implementations for the defined elements in header files. This includes:

• Function bodies: Provide the actual logic and instructions for functions.
• Internal variables: Hold data that is solely used within the implementation file and should not be accessed by other modules.

Implementation files allow you to encapsulate the specific implementation details of defined elements, ensuring that changes made to them only affect the current file.

Determining File Placement

To determine which code elements belong in a header file or an implementation file, ask yourself the following question:

• "If I change this, will I have to change code in other files to make things compile again?"

If the answer is "yes," the code element likely belongs in the header file. If the answer is "no," it should be placed in the implementation file.

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