pointers

[RoSsIaCrIiLoIA]

If sizeof(unsigned )=4 is this allowed?

#include <stdio.h>
#include <stdlib.h>

int main(void)
{unsigned *i;
i = malloc(1);
return 0;
}

and this

int main(void)
{unsigned *i;
i = malloc(1);
*i=98;
return 0;
}

[Emmanuel Delahaye]

Re: pointers

RoSsIaCrIiLoIA wrote on 28/07/04 :[color=blue]
> If sizeof(unsigned )=4 is this allowed?
>
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(void)
> {unsigned *i;
> i = malloc(1);[/color]

Yes, as far as you don't use 'i'. (Is it useful is another story).
[color=blue]
> return 0;
> }
>
> and this
>
> int main(void)
> {unsigned *i;
> i = malloc(1);
> *i=98;[/color]

No. Using 'i' invokes an undefined behaviour.
[color=blue]
> return 0;
> }[/color]


Two more things : malloc() could fail, and you are supposed to free the
allocated memory...

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html

"C is a sharp tool"

[Fred L. Kleinschmidt]

Re: pointers



RoSsIaCrIiLoIA wrote:[color=blue]
>
> If sizeof(unsigned )=4 is this allowed?
>
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(void)
> {unsigned *i;
> i = malloc(1);
> return 0;
> }
>
> and this
>
> int main(void)
> {unsigned *i;
> i = malloc(1);
> *i=98;
> return 0;
> }[/color]

Why bother? Why not just use
i = malloc(sizeof(* i));
This is the same speed and much more useful - it works on all platforms,
i.e., when sizeof(unsigned ) is 4 or 8 or anything else, and you can
change the type later and not worry about haviong to change all of the
malloc's.


--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Common User Interface Services
M/S 2R-94 (206)544-5225

[Keith Thompson]

Re: pointers

Emmanuel Delahaye <emdel@YOURBRAn oos.fr> writes:[color=blue]
> RoSsIaCrIiLoIA wrote on 28/07/04 :[color=green]
> > If sizeof(unsigned )=4 is this allowed?
> >
> > #include <stdio.h>
> > #include <stdlib.h>
> >
> > int main(void)
> > {unsigned *i;
> > i = malloc(1);[/color]
>
> Yes, as far as you don't use 'i'. (Is it useful is another story).
>[color=green]
> > return 0;
> > }
> >
> > and this int main(void)
> > {unsigned *i;
> > i = malloc(1);
> > *i=98;[/color]
>
> No. Using 'i' invokes an undefined behaviour.[/color]
[...]

Using 'i' (e.g., by comparing it to NULL) should be ok; using *i, as
the quoted code fragment does, invokes undefined behavior.

--
Keith Thompson (The_Other_Keit h) kst-u@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.

[RoSsIaCrIiLoIA]

Re: pointers

On Wed, 28 Jul 2004 15:22:56 GMT, RoSsIaCrIiLoIA <n@esiste.ee> wrote:
I forget free()[color=blue]
>If sizeof(unsigned )=4 is this allowed?
>
>#include <stdio.h>
>#include <stdlib.h>
>
>int main(void)
>{unsigned *i;
> i = malloc(1);[/color]
free(i);[color=blue]
> return 0;
>}
>
>and this
>
>int main(void)
>{unsigned *i;
> i = malloc(1);
> *i=98;[/color]
free(i);[color=blue]
> return 0;
>}[/color]