headerfile

A header file is a file in C and C++ programming languages that contains declarations of functions, macros, and variables that can be used by other source code files. These declarations essentially provide prototypes for functions and define the structure of data types, allowing the compiler to understand how to use them without needing the full implementation.

The primary purpose of header files is to promote code modularity and reusability. By placing declarations in a header, multiple source files can include it, ensuring that they all have a consistent understanding of the available functions and data structures. This prevents the need to duplicate declarations across different source files, which would be error-prone and difficult to maintain.

Common header files are often part of the standard library, providing access to fundamental functionalities like input/output operations (stdio.h), string manipulation (string.h), or mathematical functions (math.h). Developers can also create their own custom header files to organize their project's code and share declarations between different parts of their application.

When a source file includes a header file, typically using the #include directive, the preprocessor inserts the content of the header file directly into the source file before compilation. This makes the declared entities available for use in that source file. It is important to prevent multiple inclusions of the same header file within a single compilation unit to avoid errors, which is commonly achieved using include guards or #pragma once directives.