Wednesday 23 April 2014

HEADERS IN C LANGUAGE




A header file is a file with extension .h which contains C function declarations and macro definitions and to be shared between many several source files. There are two kinds of header files: the files that the programmer writes and the files that come with your compiler.
You request the use of a header file in your program by including it, with the C preprocessing directive #include like you must have seen inclusion of stdio.h header file as wll which comes along with the compiler.

Including a header file is equivalent to copying of the content of the header file but we do not do it because it will be very much error-prone and it is not a good idea to copy the content of header file into the source files, especially if there are multiple source file comprising our program.
In a simple practice program in C language, the place where we keep all the macros, constants, system wide global variables and function prototypes in the header files and include that header file wherever it is required.

SYNTAX:

Both user and system header files are included using the preprocessing directive #include. It has following two forms:

#include <abc>
This form of header is used in system header files. In this, it searches for a file named "abc" in a standard list of system directories. You can prepend directories to this list with the -I option while compiling your source code.

#include "abc"
This form of header file is used in your own programs .In this header, it searches for a file named abc in the directory containing the current file. You can also prepend directories to this list with the -I option while compiling your source code.

No comments:

Post a Comment