What Is a .H Header File (C/C++)
Updated: February 2026
The .H file format contains C or C++ header files with function declarations, macro definitions, type definitions, and constants. Header files separate interface declarations from implementation, enabling code organization and reusability.
What Header Files Contain
Header files typically include:
- Function prototypes: Declarations without implementation
- Macro definitions: #define preprocessor directives
- Type definitions: struct, typedef, class declarations
- Constants: const variables and enums
- Include guards: Prevent multiple inclusion
Using Header Files
In C/C++ source files, include headers with
#include "myheader.h"
(custom headers) or
#include <stdio.h>
(system headers). This makes declarations available to your code.
Include Guards
Header files use include guards to prevent multiple inclusion:
#ifndef MYHEADER_H
#define MYHEADER_H
// declarations
#endif
Editing Header Files
Use any text or code editor. Header files are plain text containing C/C++ code. Modern IDEs (Visual Studio, CLion) provide syntax highlighting and IntelliSense for header files.
Header File Best Practices
Keep headers minimal with only declarations, use include guards, avoid implementation in headers (except templates), and organize related declarations together.
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