«

*** post for FREE via your newsreader at post.newsfeed.com ***

Hi all,

Someone brought this up in a group I read on Yahoo!

char *p, *q;
p = malloc ( 16 );
if ( p ) {
q = p;
p = NULL;
free ( q );
}

Will this invoke UB?

Andrew


-----= Posted via Newsfeed.Com, Uncensored Usenet News =-----
http://www.newsfeed.com - The #1 Newsgroup Service in the World!
-----== 100,000 Groups! - 19 Servers! - Unlimited Download! =-----

Andrew Clark <> writes:

> char *p, *q;
> p = malloc ( 16 );
> if ( p ) {
> q = p;
> p = NULL;
> free ( q );
> }
>
> Will this invoke UB?

No. There is no reason that it should.
--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}

Andrew Clark wrote:
>
> *** post for FREE via your newsreader at post.newsfeed.com ***
>
> Hi all,
>
> Someone brought this up in a group I read on Yahoo!
>
> char *p, *q;
> p = malloc ( 16 );
> if ( p ) {
> q = p;
> p = NULL;
> free ( q );
> }
>
> Will this invoke UB?

No.
The pointer value returned by malloc,
is the pointer value which is freed.

--
pete

Andrew Clark wrote:
> *** post for FREE via your newsreader at post.newsfeed.com ***
>
> Hi all,
>
> Someone brought this up in a group I read on Yahoo!
>
> char *p, *q;
> p = malloc ( 16 );
> if ( p ) {
> q = p;
> p = NULL;
> free ( q );
> }
>
> Will this invoke UB?

Well yes, but only because of your failure to:

#include <stdlib.h>

(or, at least we can't see it (-: )

Other than that, all is well.

HTH,
--ag


--
Artie Gold -- Austin, Texas
Oh, for the good old days of regular old SPAM.

Andrew Clark wrote:

> Someone brought this up in a group I read on Yahoo!
>
> char* p = (char*)malloc(16);
> if (NULL != p) {
> char* q = p;
> p = NULL;
> free(q);
> }
>
> Will this invoke undefined behavior?

No. Neither will this

char* p = (char*)malloc(16);
char* q = p;
p = NULL;
free(q);

*** post for FREE via your newsreader at post.newsfeed.com ***

Artie Gold <> wrote in news:3FE64536.8090902
@austin.rr.com:

> Andrew Clark wrote:
>> *** post for FREE via your newsreader at post.newsfeed.com ***
>>
>> Hi all,
>>
>> Someone brought this up in a group I read on Yahoo!
>>
>> char *p, *q;
>> p = malloc ( 16 );
>> if ( p ) {
>> q = p;
>> p = NULL;
>> free ( q );
>> }
>>
>> Will this invoke UB?
>
> Well yes, but only because of your failure to:
>
> #include <stdlib.h>
>
> (or, at least we can't see it (-: )
>
> Other than that, all is well.
>
> HTH,
> --ag
>
>

Well, for my snippet I assumed that

Andrew


-----= Posted via Newsfeed.Com, Uncensored Usenet News =-----
http://www.newsfeed.com - The #1 Newsgroup Service in the World!
-----== 100,000 Groups! - 19 Servers! - Unlimited Download! =-----

E. Robert Tisdale wrote:

> Andrew Clark wrote:
>
>> Someone brought this up in a group I read on Yahoo!
>>
>> char* p = (char*)malloc(16);

>> if (NULL != p) {
>> char* q = p;
>> p = NULL;
>> free(q);
>> }
>>
>> Will this invoke undefined behavior?

This is downright malicious. You're pretending to quote someone else, but
have gratuitously added a cast where none exists in the original, apart
from making other unnecessary and unmarked changes. Please don't attribute
your words to someone else. In real life it would be called forgery, and
is a felony.

-nrk.

>
> No. Neither will this
>
> char* p = (char*)malloc(16);
> char* q = p;
> p = NULL;
> free(q);

On Mon, 22 Dec 2003 01:38:32 UTC, "E. Robert Tisdale"
<> wrote:

> Andrew Clark wrote:
>
> > Someone brought this up in a group I read on Yahoo!
> >
> > char* p = (char*)malloc(16);
> > if (NULL != p) {
> > char* q = p;
> > p = NULL;
> > free(q);
> > }
> >
> > Will this invoke undefined behavior?
>
> No. Neither will this

Wrong. It occures undefined behavior when you forget to include
stdlib.h. You hides the diagnostic saying that you tries to convert
int to a pointer throu casting the value the compiler things it were
int to a pointer.

> char* p = (char*)malloc(16);

The same bug as above - resulting in undefined behavior.

> char* q = p;
> p = NULL;
> free(q);
>

That's fine - but lets q hold an indetermined value (the pointer in it
points to somewhere but not to an address guilty for your program)
after free.

--
Tschau/Bye
Herbert

Visit http://www.ecomstation.de the home of german eComStation

nrk <> spoke thus:

> E. Robert Tisdale wrote:
>>>
>>> char* p = (char*)malloc(16);

> This is downright malicious.

From Tisdale?? Never! I propose, actually, that a section of the FAQ
be devoted to identifying known trolls and such (21.1 - "Who is E.
Robert Tisdale?") for the benefit of those who might otherwise be
seduced by their wiles... 21.2 should be "What is a killfile?"

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cyberspace.org | don't, I need to know. Flames welcome.

nrk wrote:
>
.... snip Trollsdale stuff ...
>
> This is downright malicious. You're pretending to quote someone
> else, but have gratuitously added a cast where none exists in the
> original, apart from making other unnecessary and unmarked changes.
> Please don't attribute your words to someone else. In real life it
> would be called forgery, and is a felony.

This is just standard procedure for ERTisdale, better known as
Trollsdale. He has made himself almost as obnoxious as possible
in his inimitably ignorant way.

--
Chuck F () ()
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!