Saturday, April 24, 2010

Difference between #include and #include "stdio.h"

Many of you confused with this two method of specifying the include files. This article will teach you what the difference between these two is.

#include <stdio.h>

This method of specifying is used to include the standard header files.
The standard header files are in "include" folder. Files which are in "include" folder are specified by #include <file.h>
files should be in "include" folder.

#include "stdio.h"

This method of specifying is used to include the user defined files. On other hand,the file should be in current folder.

1 comments:

When writing your C program, you can include files in two ways. The first way is to surround the file you
want to include with the angled brackets < and >. This method of inclusion tells the preprocessor to look for the file in the predefined default location. This predefined default location is often an INCLUDE environment variable that denotes the path to your include files. For instance, given the INCLUDE variable

INCLUDE=C:COMPILERINCLUDE;S:SOURCEHEADERS;

using the #include version of file inclusion, the compiler first checks the C:COMPILERINCLUDE
directory for the specified file. If the file is not found there, the compiler then checks the
S:SOURCEHEADERS directory. If the file is still not found, the preprocessor checks the current directory.

The second way to include files is to surround the file you want to include with double quotation marks. This method of inclusion tells the preprocessor to look for the file in the current directory first, then look for it in the predefined locations you have set up. Using the #include ?file? version of file inclusion and applying it to the preceding example, the preprocessor first checks the current directory for the specified file. If the file is not found in the current directory, the C:COMPILERINCLUDE directory is searched. If the file is still not found, the preprocessor checks the S:SOURCEHEADERS directory.
The #include method of file inclusion is often used to include standard headers such as stdio.h or
stdlib.h. This is because these headers are rarely (if ever) modified, and they should always be read from your compiler?s standard include file directory.

The #include ?file? method of file inclusion is often used to include nonstandard header files that you have created for use in your program. This is because these headers are often modified in the current directory, and you will want the preprocessor to use your newly modified version of the header rather than the older, unmodified version.

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