preprocessing statements

[Bill Cunningham]

I have been thinking about hiding headers from my compiler's
preprocessor and allowing others to be shown. I want to use the most used
and add others is necessary. Would this be how it is properly done. I want
to ask ahead of time because what I do might work but it might not be the
"correct" or standard way.

#include <stdio.h>
#include <stdlib.h>
#ifdef LINUX
#include <unistd.h>
#include <sys/types>
#include <sys/stats.h>
#include <fctnl.h>
#endif

Is the #endif needed at the end of this case ?

Bill

[Walter Roberson]

In article <vXX_j.5092$nx6 .2636@trnddc03> ,
Bill Cunningham <no****@nspam.c omwrote:

>#include <stdio.h>
#include <stdlib.h>
#ifdef LINUX
#include <unistd.h>
#include <sys/types>
#include <sys/stats.h>
#include <fctnl.h>
#endif

Is the #endif needed at the end of this case ?

Yes. Every #if or #ifdef must have a matching #endif
--
"We may gather out of history a policy, by the comparison and
application of other men's forepassed miseries with our own like
errors and ill deservings." -- Sir Walter Raleigh

[vippstar]

On May 27, 8:56 pm, "Bill Cunningham" <nos...@nspam.c omwrote:

I have been thinking about hiding headers from my compiler's
preprocessor and allowing others to be shown. I want to use the most used
and add others is necessary. Would this be how it is properly done. I want
to ask ahead of time because what I do might work but it might not be the
"correct" or standard way.

That doesn't make sense, please re-attempt to explain your intentions,
without being so ambiguous/vague.

#include <stdio.h>
#include <stdlib.h>
#ifdef LINUX
#include <unistd.h>
#include <sys/types>
#include <sys/stats.h>
#include <fctnl.h>

Just what is wrong with you Bill?
Haven't you understood yet such thing is not topical for comp.lang.c?

#endif

Is the #endif needed at the end of this case ?

What's so hard about removing it and trying to compile? Or reading
about #ifdef in your book?
Isn't it the obvious thing to do before asking a group of people about
it?

[Bill Cunningham]

"santosh" <sa*********@gm ail.comwrote in message
news:g1******** **@registered.m otzarella.org.. .

>>Seriously though, no preprocessing directives are perfectly topical.
vippstar was talking about the various system specific headers that
you had included in your code. Those _are_ OT and I believe better
addressed in comp.unix.progr ammer. But your actual question can be
answered here and Walter Roberson did so. Also your method to
conditional ly compile the include directives is perfectly fine.
That's how it's done.

[snip]

So then is it ok to talk about and use examples of #if and #ifdef and so
on. Or is preprocessing directives OT ?

Bill

[Walter Roberson]

In article <y3Z_j.3437$fk. 3100@trnddc06>,
Bill Cunningham <no****@nspam.c omwrote:

My question was about preprocessor directives. Yes it was a typo. The
headers I posted if they were relevant to the question I understand would be
off topic. They were just an example of using the preprocessor to block out
headers not needed. The question concern #if and #ifdef which seems to be it
looks like now to mean the same thing. #endif also was inquired to.

In this thread you did not ask about #if vs #ifdef . They do not mean
the same thing. For example,

#define FOO 0
#ifdef FOO
/* this section *will* be compiled, because FOO -is- defined. */
#endif
#if FOO
/* this section will *not* be compiled, because FOO's value is 0,
and #if 0 is false */
#endif
#ifdef if
/* this section will *not* be compiled, because the macro if is -not-
defined. */
#endif
#if !if
/* this section *will* be compiled. In a #if line, after all known
macros are expanded, all remaining identifiers have the value 0
substituted, without any consideration as to whether the identifiers
might be C keywords or library functions. With no macro named if,
the line would be equivilent to #if !0 which is #if 1 which is true. */
#endif
--
"The whole history of civilization is strewn with creeds and
institutions which were invaluable at first, and deadly
afterwards." -- Walter Bagehot

[Walter Roberson]

In article <A9Z_j.3439$fk. 489@trnddc06>,
Bill Cunningham <no****@nspam.c omwrote:

So then is it ok to talk about and use examples of #if and #ifdef and so
on. Or is preprocessing directives OT ?

preprocessing directives are on-topic . There is only a problem if
the specific content of any #include'd non-standard file is relevant
to the question -- though questions about which identifiers are
predefined for specific implementations would also be off-topic
(except for the small number of identifiers documented in the C standard.)
--
"Let me live in my house by the side of the road --
It's here the race of men go by.
They are good, they are bad, they are weak, they are strong
Wise, foolish -- so am I;" -- Sam Walter Foss

[Keith Thompson]

"Bill Cunningham" <no****@nspam.c omwrites:
[...]

My question was about preprocessor directives. Yes it was a typo. The
headers I posted if they were relevant to the question I understand would be
off topic. They were just an example of using the preprocessor to block out
headers not needed. The question concern #if and #ifdef which seems to be it
looks like now to mean the same thing. #endif also was inquired to.

No, #if and #ifdef are similar, but they don't mean the same thing.
Consult your text book to learn the difference.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Bill Cunningham]

"Walter Roberson" <ro******@ibd.n rc-cnrc.gc.cawrote in message
news:g1******** **@canopus.cc.u manitoba.ca...

In this thread you did not ask about #if vs #ifdef . They do not mean
the same thing. For example,

#define FOO 0
#ifdef FOO
/* this section *will* be compiled, because FOO -is- defined. */
#endif
#if FOO
/* this section will *not* be compiled, because FOO's value is 0,
and #if 0 is false */
#endif
#ifdef if
/* this section will *not* be compiled, because the macro if is -not-
defined. */
#endif
#if !if
/* this section *will* be compiled. In a #if line, after all known
macros are expanded, all remaining identifiers have the value 0
substituted, without any consideration as to whether the identifiers
might be C keywords or library functions. With no macro named if,
the line would be equivilent to #if !0 which is #if 1 which is true.
*/
#endif

Priceless.

Bill

[Keith Thompson]

"Bill Cunningham" <no****@nspam.c omwrites:

I have been thinking about hiding headers from my compiler's
preprocessor and allowing others to be shown. I want to use the most used
and add others is necessary. Would this be how it is properly done. I want
to ask ahead of time because what I do might work but it might not be the
"correct" or standard way.

#include <stdio.h>
#include <stdlib.h>
#ifdef LINUX
#include <unistd.h>
#include <sys/types>
#include <sys/stats.h>
#include <fctnl.h>
#endif

Is the #endif needed at the end of this case ?

One more thing that you didn't ask about (but probably should have):

How do you expect the symbol LINUX to be defined? Since that
identifier must be available for use in programs, an implementation is
not allowed to pre-define it. There may be other symbols that are
predefined (if you're trying to determine whether you're on a Linux
system); which symbols those might be is a question for another forum.

If you're defining it yourself, that's fine, but you didn't show that.

Also, you appear to be trying to write code that will use things
declared in those implementation-defined headers if you're on a Linux
system, but will still compile and work properly otherwise. Such
things are doable, but the nature of the questions you've been asking
here suggest to me that this is a more advanced topic than you're
ready for.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Keith Thompson]

"Bill Cunningham" <no****@nspam.c omwrites:

"santosh" <sa*********@gm ail.comwrote in message
news:g1******** **@registered.m otzarella.org.. .

>>>Seriously though, no preprocessing directives are perfectly topical.
vippstar was talking about the various system specific headers that
you had included in your code. Those _are_ OT and I believe better
addressed in comp.unix.progr ammer. But your actual question can be
answered here and Walter Roberson did so. Also your method to
conditionall y compile the include directives is perfectly fine.
That's how it's done.

[snip]

So then is it ok to talk about and use examples of #if and #ifdef and so
on. Or is preprocessing directives OT ?

Preprocessing directives are topical. In my opinion, the person who
complained that your orginal post was off-topic overreacted.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"