The .h++ file extension is typically associated with C++ header files. Header files in C++ (and C) serve as interfaces between different parts of a program or between different programs. They contain declarations of functions, classes, variables, and other program elements, but generally not the actual implementations (definitions) of those elements. The purpose of a header file is to allow different source code files to share these declarations without having to duplicate them. This promotes code reusability, modularity, and maintainability. When a source code file includes a header file (using the #include directive), the compiler effectively copies the contents of the header file into the source code file before compilation. This allows the compiler to check that functions are called with the correct arguments, that variables are used with the correct types, and that classes are used according to their defined interfaces. Header files are crucial for organizing large C++ projects and for creating libraries that can be used by multiple programs.