Re: what will be the value of #define

Keith Thompson wrote:
"raghu" <ragavakumar@xxxxxxxxx> writes:
On Mar 2, 6:28 pm, mark_blue...@xxxxxxxxx wrote:

<snip>

To explain a little more for "raghu" - the approach is a standard
convention for ensuring that multiple inclusions of header files
(usually due to being nested in other header files) are "harmless".

If my header called "fred.h" has the form:-

#ifndef FRED_H
#define FRED_H
...
#endif /*FRED_H*/

then the first inclusion will have the macro "FRED_H" undefined, will
define the macro (as an empty macro) and do the other declarations,
definitions etc which the header defines.

Any subsequent inclusions will have "FRED_H" defined, so will do
nothing.

Yes you are correct. I am imlementing exactly like this but one thing
I didn't understand what will be the value assigned FRED_H here. when
the processor looks in to it their must be change in the value. Right.
what will be that value.

Thanks for ur reply.

<snip>

Given

#define SYSTEM_H

the identifier SYSTEM_H is a macro that expands to nothing. Any uses
of it *outside a preprocessing directive* (such as #if or #ifdef) will
simply vanish. For example, this:
SYSTEM_H int x SYSTEM_H = 42 SYSTEM_H ;
is exactly equivalent to this:
int x = 42 ;

A minor question:

Is it simply removed or is it replaced by a space character?

<snip>

.

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