A .hpp file is a C++ header file, serving a similar purpose to .h or .hh files in C++ programming. These files primarily contain declarations of functions, classes, templates, and global variables, but typically not their definitions (implementations). The main role of a header file is to provide an interface that other source files (.cpp files) can include to access the code defined elsewhere. When a .cpp file includes a .hpp file using the #include preprocessor directive, the contents of the header file are effectively copied into the source file before compilation. This process allows the compiler to understand the signatures and structures of the components being used, ensuring type safety and facilitating correct linking during the build process. The .hpp extension is often used to explicitly denote a C++ header file, differentiating it from C header files (.h), or sometimes specifically for header-only libraries where the entire implementation, often involving templates, is contained within the header itself. Header guards (e.g., using #ifndef, #define, #endif or #pragma once) are essential in .hpp files to prevent multiple inclusions, which can lead to redefinition errors and compilation failures. These files are plain text and are edited using standard text editors or Integrated Development Environments (IDEs).