What's the Difference Between .h (Header) and .cpp (Code) Files in C ?

Understanding the Distinction Between .h and .cpp Files

When dividing code into multiple files, understanding the purpose of each file is crucial. A fundamental question arises: what information should be included in the .h header file and what should remain in the .cpp code file?

Header Files (.h): The Definition Repository

Header files (.h) serve as repositories for definitions that are commonly needed across multiple files. These definitions typically include:

• Class Declarations: Defining the structure and members of classes that encapsulate data and behavior.
• Function Prototypes: Declaring the signatures of functions, specifying their return types, parameter lists, and exceptions.
• Enumerations: Defining symbolic names for a set of values, facilitating readability and maintainability.

In essence, anything that "defines" something belongs in a header file. These definitions allow different modules of your code to interact with each other consistently.

Code Files (.cpp): The Implementation Workspace

Code files (.cpp) contain the actual implementation of functions and logic. This includes:

• Function Bodies: The code that provides the specific functionality for each function, including the sequence of instructions to be executed.
• Internal Variables: Local variables whose scope is limited to a single file and should not be accessed by other modules.

In summary, implementation details that are self-contained within a single file belong in code files (.cpp).

A Simple Rule of Thumb

To determine the appropriate placement of code elements, ask yourself: "If I change this, will I need to modify other files to ensure compilation success?" If the answer is yes, the code element likely belongs in the header file. If no, it should reside in the code file.

By adhering to this distinction, you can effectively structure your code, ensuring clarity, modularity, and maintainability.

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