C Programming - C Preprocessor - Discussion

We include files into our source as follows:

In case of files placed in your _include_ dir
which you tell the compiler to look into
#include <filename.ext>

In case of other files, which are not in compiler's known include dir
#include "relative/path/to/filename.ext".

In either case, what the pre-possessor does is pretty simple. It reads the whole content of that file and replaces this line with *the whole content*. That's it. Nothing more, nothing less.

Any extension is fine as long as you keep text data into it which it could "include". Any extension and any text content should work.

Haven't given it a try, but if a binary format file (like an image) is included, the preprocessor will most likely read it as ASCII files and copy it too, and then complain about the grammar.

@ALL

Is is necessary that a header files should have ".h" ?

Answer is NO.

Because the header files can have any extension but it should be included with in C program with same extension.

Let me explain what I did to check this...

In Turbo C directory

C:\Turbo>copy stdio.h stdio.hdr
C:\Turbo>copy conio.h conio.exe

Then I used the line following line to include the header file.

#include<stdio.hdr>
#include<conio.exe>
void main()
{
printf("Welcome to IndiaBIX.com !");
getch();
}

The output : Welcome to IndiaBIX.com !

@ALl.

vi hi.q
{
#include<stdio.h>
}

vi prog.c
#include"hi.q"
int main()
{
printf("in prog.c file\n");
}

cc hi.q prog.c
o/p error: file format not recognized
But if we use with hi.h, then it's working properly. so, I think the extension should be .h only.

@Sundar.

It's NOT WORKS IN code blocks.

#include<stdio.hdr>
#include<conio.exe>
void main()
{
printf("Welcome to IndiaBIX.com !");
getch();
}

The output : Welcome to IndiaBIX.com!

#include"filename.c".

"this is also a header file".

In a extern concept, many different files can use same variable.

By using include the whole file.

That's all about it.

Thanks.

We know that we use many headder file such as

stdio.h, dos.h, conio.h, stdlib.h, graphics.h, iostream.h etc.

So how can you say that there is no need of this extension ?

Header files can have any extension but it should be included with in C program with same extension.

We can define filename.c in header file.

We can define fact.c, filename.c in header file.

So, if you mention filename.c, it will read the entire file.

Header files only puts the contents whatever it have on the top of program so it may have any other extension.

Without .h extension it is not possible to include the function like printf, scanf etc.