Header files

Header files

C/C++ has a number of header files that hold the information it needs to know about the library functions. They provide function prototype declarations for library functions. Data types and symbolic constants used with the library functions are also defined in them; along with global variables defined by the library functions. Header files are required by the include directives because include directives are always placed at the head of a C program. The < > (angle bracket) around a header file tells the C preprocessor to look for the header file in a directory other than the “code”.



Frequently used Header Files


Some of the frequently used header files, and library functions they contain are listed below.
<stdio.h>        Defines the standard I/O predefined streams, stdin, stdout, stdprn and stderr and declares
                      stream-level I/O routines.
<stdlib.h>       Declares several commonly used routines: conversion routines, search/sort routines and other
                       miscellany.
<string.h>       Declares several string and memory manipulation routines.
<search.h>     Declares functions for searching and sorting.
<memory.h>   Declares memory manipulation functions
<mem.h>        Declares memory manipulation functions
<math.h>        Declares prototypes for the math functions
<malloc.h>     Declares memory management functions and variables.
<io.h>            Contains structures and declarations for low level input/output routines.
<graphics.h>   Declares prototypes for graphics functions
<float.h>          Contains parameters for floating point routines.
<errno.h>         Defines constant mnemonics for the error codes.
<dos.h>           Defines various constants and gives declarations needed for DOS and 8086 specific calls.
<dir.h>             Contains structures, macros and functions for working with directories and path names.
<ctype.h>         Contains information used by the character classification and character conversion macros.
<conio.h>         Declares various functions used in calling the DOS console I/O routines.
<complex.h>    Declares the C++ complex math functions.
<bios.h>           Declares various functions used in calling IBM-PC ROM BIOS routines.
<alloc.h>         Declares memory management functions. (allocation, deallocation etc.)
<time.h>          Defines a structure filled in by the time conversion routines and a type used by other time
                      routines also provides prototypes for these routines.