malloc without stdlib.h

[Anton Dec]

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?

[Joe Wright]

Fr************@ googlemail.com wrote:

On Jun 8, 9:16 pm, Keith Thompson <[e-mail] ote:

>"Army1987" <please....@for .itwrites:

>>"Jack Klein" <jackkl...@spam cop.netha scritto nel messaggio
news:pv****** *************** ***********@4ax .com...
On Wed, 6 Jun 2007 00:42:03 +0200 (CEST), Anton Dec
<anton...@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);
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
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.

I wonder if you are missing the difference between 'declare' and
'define' in terms of headers. A header provides the compiler with
information about things. These bits of information are 'declarations'
and do not take up memory. In stdlib.h we find something like..

void *malloc(size_t) ;

This is a declaration and in fact a prototype. It is not a definition.

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Francine.Neary]

On Jun 8, 11:58 pm, Joe Wright <joewwri...@com cast.netwrote:

I wonder if you are missing the difference between 'declare' and
'define' in terms of headers. A header provides the compiler with
information about things. These bits of information are 'declarations'
and do not take up memory. In stdlib.h we find something like..

void *malloc(size_t) ;

This is a declaration and in fact a prototype. It is not a definition.

That's right. But the whole point of the preceding discussion was:
could an implementation put a definition (*not* just a declaration) of
malloc in stdlib.h?

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---