Because there are many header files for the object code in the standard library file, each header file covers only a fraction of the functions in the standard library file. The reason is that many C compilers bring into your program every function mentioned in a header fileeven those functions that you do not use. By creating multiple header files, a library's author makes it possible for you to use the library file selectively, reducing the degree to which your programs are bloated with functions that you do not use.