Just curious about this...
malloc is defined in stdlib.h, right?
But if I write a program without #include<stdlib .hand use malloc, it
still works as expected.
Why is this? Is malloc automatically linked from somewhere else
magically?
Jun 5 '07
21  5437 
"Jack Klein" <ja*******@spam cop.netha scritto nel messaggio
news:pv******** *************** *********@4ax.c om...
On Wed, 6 Jun 2007 00:42:03 +0200 (CEST), Anton Dec
<an******@maili nator.comwrote in comp.lang.c:
>Just curious about this...
malloc is defined in stdlib.h, right?
No, malloc() is prototyped in <stdlib.h>. I suppose it is possible
that there is at least one C implementation out there that actually
defines malloc() in <stdlib.h>, but I certainly don't expect to ever
find one.
The standard (7.1.4) guarantees that I can use malloc if I write
#include <stddef.h/* for size_t */
extern void *malloc(size_t size);
If malloc is defined in <stdlib.hthis is not possible.
Army1987 wrote On 06/08/07 09:40,:
"Jack Klein" <ja*******@spam cop.netha scritto nel messaggio
news:pv******** *************** *********@4ax.c om...
>>On Wed, 6 Jun 2007 00:42:03 +0200 (CEST), Anton Dec
<an******@mai linator.comwrot e in comp.lang.c:
>>>Just curious about this...
malloc is defined in stdlib.h, right?
No, malloc() is prototyped in <stdlib.h>. I suppose it is possible
that there is at least one C implementation out there that actually
defines malloc() in <stdlib.h>, but I certainly don't expect to ever
find one.
The standard (7.1.4) guarantees that I can use malloc if I write
#include <stddef.h/* for size_t */
extern void *malloc(size_t size);
Yes, any Standard library function must work if
declared as the Standard describes it, whether or not
the associated header is included. (For some functions,
correct declarations are impossible without the header,
but malloc() is not one of those.)
However, it's unwise to write free-hand declarations
like this. The function will work, but may not work
optimally if its declaration omits implementation-specific
magic that informs the compiler of some shortcuts or tricks
it can usefully take. getchar() and putchar() are classic
examples along these lines, but other functions may also
work better if declared magically:
void * _no_effect_on_e rrno_ malloc(size_t);
If malloc is defined in <stdlib.hthis is not possible.
I don't see why not. I've seen definitions -- yes,
definitions -- of toupper() et al. in <ctype.h>, so I see
no a priori reason to believe malloc() could not be done
the same way. It would be surprising, given malloc()'s
greater complexity, but not out of the question.
-- Er*********@sun .com
Eric Sosman wrote:
I don't see why not. I've seen definitions -- yes,
definitions -- of toupper() et al. in <ctype.h>, so I see
no a priori reason to believe malloc() could not be done
the same way. It would be surprising, given malloc()'s
greater complexity, but not out of the question.
The defined malloc might be a shim:
void* malloc( size_t n )
{ return _slightly_broke n_system_malloc ( n + 3 ); }
--
"We are on the brink of a new era, if only --" /The Beiderbeck Affair/
Hewlett-Packard Limited registered no:
registered office: Cain Road, Bracknell, Berks RG12 1HN 690597 England
Army1987 wrote:
>
.... snip ...
>
The standard (7.1.4) guarantees that I can use malloc if I write
#include <stddef.h/* for size_t */
extern void *malloc(size_t size);
If malloc is defined in <stdlib.hthis is not possible.
Yes it is. Besides which I see no such clause in N869. Use stdlib.
--
<http://www.cs.auckland .ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfoc us.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
<http://kadaitcha.cx/vista/dogsbreakfast/index.html>
cbfalconer at maineline dot net
--
Posted via a free Usenet account from http://www.teranews.com
"Eric Sosman" <Er*********@su n.comha scritto nel messaggio
news:1181317044 .599380@news1nw k...
Army1987 wrote On 06/08/07 09:40,:
>"Jack Klein" <ja*******@spam cop.netha scritto nel messaggio
news:pv******* *************** **********@4ax. com...
>>>On Wed, 6 Jun 2007 00:42:03 +0200 (CEST), Anton Dec
<an******@ma ilinator.comwro te in comp.lang.c:
Just curious about this...
malloc is defined in stdlib.h, right?
No, malloc() is prototyped in <stdlib.h>. I suppose it is possible
that there is at least one C implementation out there that actually
defines malloc() in <stdlib.h>, but I certainly don't expect to ever
find one.
The standard (7.1.4) guarantees that I can use malloc if I write
#include <stddef.h/* for size_t */
extern void *malloc(size_t size);
Yes, any Standard library function must work if
declared as the Standard describes it, whether or not
the associated header is included. (For some functions,
correct declarations are impossible without the header,
but malloc() is not one of those.)
However, it's unwise to write free-hand declarations
like this.
I've not saying that it is not a Bad Thing to do that, only that
the standard explicitly allows it.
"Army1987" <pl********@for .itwrites:
"Jack Klein" <ja*******@spam cop.netha scritto nel messaggio
news:pv******** *************** *********@4ax.c om...
>On Wed, 6 Jun 2007 00:42:03 +0200 (CEST), Anton Dec
<an******@mail inator.comwrote in comp.lang.c:
>>Just curious about this...
malloc is defined in stdlib.h, right?
No, malloc() is prototyped in <stdlib.h>. I suppose it is possible
that there is at least one C implementation out there that actually
defines malloc() in <stdlib.h>, but I certainly don't expect to ever
find one.
The standard (7.1.4) guarantees that I can use malloc if I write
#include <stddef.h/* for size_t */
extern void *malloc(size_t size);
If malloc is defined in <stdlib.hthis is not possible.
This started, I think, because a previous poster misunderstood the
difference between a declaration and a definition.
I'm not sure about Army1987's argument, but if malloc were actually
*defined* in <stdlib.h>, then a program in which two separately
compiled translation units both have "#include <stdlib.h>" would have
two definitions of malloc. I believe that would render the
implementation non-conforming; a legal program would fail, probably
with a link-time error message.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
On Jun 8, 9:16 pm, Keith Thompson <k...@mib.orgwr ote:
"Army1987" <please....@for .itwrites:
"Jack Klein" <jackkl...@spam cop.netha scritto nel messaggio
news:pv******** *************** *********@4ax.c om...
On Wed, 6 Jun 2007 00:42:03 +0200 (CEST), Anton Dec
<anton...@maili nator.comwrote in comp.lang.c:
>Just curious about this...
>malloc is defined in stdlib.h, right?
No, malloc() is prototyped in <stdlib.h>. I suppose it is possible
that there is at least one C implementation out there that actually
defines malloc() in <stdlib.h>, but I certainly don't expect to ever
find one.
The standard (7.1.4) guarantees that I can use malloc if I write
#include <stddef.h/* for size_t */
extern void *malloc(size_t size);
If malloc is defined in <stdlib.hthis is not possible.
This started, I think, because a previous poster misunderstood the
difference between a declaration and a definition.
I'm not sure about Army1987's argument, but if malloc were actually
*defined* in <stdlib.h>, then a program in which two separately
compiled translation units both have "#include <stdlib.h>" would have
two definitions of malloc. I believe that would render the
implementation non-conforming; a legal program would fail, probably
with a link-time error message.
Isn't it required that including a header from the standard library
more than once is equivalent to including it once? In that case it
would be fine to define malloc in stdlib.h, as long as there was an
include-guard #define'd to ensure the definition was only included
once even if the header was #included more than once.
--
Keith Thompson (The_Other_Keit h) k...@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Fr************@ googlemail.com writes:
On Jun 8, 9:16 pm, Keith Thompson <k...@mib.orgwr ote:
[...]
>This started, I think, because a previous poster misunderstood the
difference between a declaration and a definition.
I'm not sure about Army1987's argument, but if malloc were actually
*defined* in <stdlib.h>, then a program in which two separately
compiled translation units both have "#include <stdlib.h>" would have
two definitions of malloc. I believe that would render the
implementati on non-conforming; a legal program would fail, probably
with a link-time error message.
Isn't it required that including a header from the standard library
more than once is equivalent to including it once? In that case it
would be fine to define malloc in stdlib.h, as long as there was an
include-guard #define'd to ensure the definition was only included
once even if the header was #included more than once.
Including it multiple times is equivalent to including it once *within
a translation unit*. A program can be composed of multiple
translation units (separately compiled, joined together by the
linker).
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
On Jun 8, 9:36 pm, Keith Thompson <k...@mib.orgwr ote:
Francine.Ne...@ googlemail.com writes:
On Jun 8, 9:16 pm, Keith Thompson <k...@mib.orgwr ote:
[...]
This started, I think, because a previous poster misunderstood the
difference between a declaration and a definition.
I'm not sure about Army1987's argument, but if malloc were actually
*defined* in <stdlib.h>, then a program in which two separately
compiled translation units both have "#include <stdlib.h>" would have
two definitions of malloc. I believe that would render the
implementation non-conforming; a legal program would fail, probably
with a link-time error message.
Isn't it required that including a header from the standard library
more than once is equivalent to including it once? In that case it
would be fine to define malloc in stdlib.h, as long as there was an
include-guard #define'd to ensure the definition was only included
once even if the header was #included more than once.
Including it multiple times is equivalent to including it once *within
a translation unit*. A program can be composed of multiple
translation units (separately compiled, joined together by the
linker).
Ah, I see what you mean. That does seem to imply that malloc can't be
defined in stdlib.h then.
--
Keith Thompson (The_Other_Keit h) k...@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Fr************@ googlemail.com writes:
[...]
Ah, I see what you mean. That does seem to imply that malloc can't be
defined in stdlib.h then.
It can, of course, be defined as a macro.
It's conceivable that there's some tricky way it could be defined as a
function, perhaps with some sort of compiler magic, but there wouldn't
be much point in doing so.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister" This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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