In Chapter 11, Table 11-1 presented a number of standard C header files that are available for use in your programs. Most of these header files are used in conjunction with their associated Standard C library and the functions they hold. A C library is nothing more than a group of (often related) functions that have been precompiled into what is called a library file. Conceptually, you can think of a library file as being organized like a book. At the front of the file is an index of each function name that appears in the library, followed by a byte offset that tells where the code for that function can be found in the file, along with the byte-length of the function. With this information, the compiler is able to extract the code for any given function from that library and insert it into your program.