Are the standard header files (<stdio.hfor example) always safe to include
more than once?
Is this just good programming practice on the part of the average person who
writes these things, or is this guaranteed in a standard?
------------------------------------------------------------
David T. Ashley (dt*@e3ft.com) http://www.e3ft.com (Consulting Home Page) http://www.dtashley.com (Personal Home Page) http://gpl.e3ft.com (GPL Publications and Projects) 7 1759
David T. Ashley wrote:
Are the standard header files (<stdio.hfor example) always safe to include
more than once?
Yes
Is this just good programming practice on the part of the average person who
writes these things, or is this guaranteed in a standard?
It is - 7.1.2 paragraph 4.
--
Ian Collins.
David T. Ashley wrote:
Are the standard header files (<stdio.hfor example) always safe to include
more than once?
Is this just good programming practice on the part of the average person who
writes these things, or is this guaranteed in a standard?
It's guaranteed, with one exception. 7.1.2p4 states:
"Standard headers may be included in any order; each may be included
more than once in a given scope, with no effect different from being
included only once, except that the effect of including <assert.h>
depends on the definition of NDEBUG (see 7.2). [...]"
David T. Ashley wrote:
Are the standard header files (<stdio.hfor example) always safe to include
more than once?
Actually, many header file uses pre-processor statement
#ifndef INCLUDE
#define INCLUDE 1
....
....
....
#endif
which would take care that contents of the header are not replaced
again by the pre-processor... sa*****@yahoo.c o.in said:
>
David T. Ashley wrote:
>Are the standard header files (<stdio.hfor example) always safe to include more than once?
Actually, many header file uses pre-processor statement
#ifndef INCLUDE
#define INCLUDE 1
...
...
...
#endif
which would take care that contents of the header are not replaced
again by the pre-processor...
Nor would any other header that used the same identifier. Fortunately, that
isn't how things are done.
You pick a *unique* name, e.g. something like:
#ifndef H_CUSTOMER_HEAD ER
#define H_CUSTOMER_HEAD ER 1
....
#endif
That way, you don't disable other headers further down the list.
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk
email: rjh at the above domain, - www.
"Richard Heathfield" <rj*@see.sig.in validwrote in message
sa*****@yahoo.c o.in said:
>> David T. Ashley wrote:
>>Are the standard header files (<stdio.hfor example) always safe to include more than once? Actually, many header file uses pre-processor statement
#ifndef INCLUDE #define INCLUDE 1 ... ... ... #endif
which would take care that contents of the header are not replaced again by the pre-processor...
Nor would any other header that used the same identifier. Fortunately,
that
isn't how things are done.
You pick a *unique* name, e.g. something like:
#ifndef H_CUSTOMER_HEAD ER
#define H_CUSTOMER_HEAD ER 1
...
#endif
That way, you don't disable other headers further down the list.
#ifndef foo_h
#define foo_h
/* foo.h - defines a wonderful function */
double foo(int x);
#endif
No need to define as 1
Malcolm McLean said:
<snip>
#ifndef foo_h
#define foo_h
/* foo.h - defines a wonderful function */
double foo(int x);
#endif
No need to define as 1
True enough. I do it anyway, against the possibility that I might one day
find a use for changing it to 2. :-)
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk
email: rjh at the above domain, - www.
"Richard Heathfield" <rj*@see.sig.in validwrote in message
news:ha******** *************@b t.com...
True enough. I do it anyway, against the possibility that I might one day
find a use for changing it to 2. :-)
Just thinking about it, defining as 1 helps makes it possible to use both
#if !foo_h
and
#ifndef
I never do it though :) This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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