realloc

[D²]

Hello,
I was trying to enlarge the size of an array wqith this code:

float data [100];

data = realloc (data, n*sizeof(float) );

but I encountered an error during compile fase, is this sintax right? How
can should I do?

thank you all

Daniele

[Walter Roberson]

Re: realloc

In article <wJS9e.58204$IN .1027775@twiste r2.libero.it>,
D² <spectrix@wind. it> wrote:[color=blue]
>I was trying to enlarge the size of an array wqith this code:
>float data [100];
>data = realloc (data, n*sizeof(float) );[/color]

You can only realloc() space that was dynamically allocated,
such as via malloc() or alloc() .
--
"This was a Golden Age, a time of high adventure, rich living and
hard dying... but nobody thought so." -- Alfred Bester, TSMD

[Keith Thompson]

Re: realloc

roberson@ibd.nr c-cnrc.gc.ca (Walter Roberson) writes:[color=blue]
> In article <wJS9e.58204$IN .1027775@twiste r2.libero.it>,
> D² <spectrix@wind. it> wrote:[color=green]
>>I was trying to enlarge the size of an array wqith this code:
>>float data [100];
>>data = realloc (data, n*sizeof(float) );[/color]
>
> You can only realloc() space that was dynamically allocated,
> such as via malloc() or alloc() .[/color]

What is alloc()? Do you mean calloc()?

--
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.

[Al Bowers]

Re: realloc



Walter Roberson wrote:[color=blue]
> In article <wJS9e.58204$IN .1027775@twiste r2.libero.it>,
> D² <spectrix@wind. it> wrote:
>[color=green]
>>I was trying to enlarge the size of an array wqith this code:
>>float data [100];
>>data = realloc (data, n*sizeof(float) );[/color]
>
>
> You can only realloc() space that was dynamically allocated,
> such as via malloc() or alloc() .[/color]

The first arguement in function realloc may have a NULL value
which makes the function behave like function malloc for the
requested space. 'data' must have either the value of NULL or
a value previously returned by function malloc, calloc, or
realloc.

In the above realloc statement, it is unwise to assign the
return value of function realloc to 'data'. If the function
returned NULL, 'data' with have that NULL value and the previous
value of 'data' which may have been a pointer to allocated memory
would be lost making the space unaccessible for use
or for freeing the space.

Typically, one will make the allocations as follows.

#include <stdlib.h>

float *data = NULL;
float *tmp;
size_"t n;

n = 15;
tmp = realloc(data,n * sizeof *data);
if(tmp != NULL)
{
data = tmp;
/* use the storage */
}
n = 8;
tmp = realloc(data,n * sizeof *data);
if(tmp != NULL)
{
data = tmp;
/* use the storage */
}
free(data); /* Finished with it */
data = NULL; /* put it back to NULL */



--
Al Bowers
Tampa, Fl USA
mailto: xabowers@myrapi dsys.com (remove the x to send email)

http://www.geocities.com/abowers822/

[D²]

Re: realloc

Thank you all again!
bye

[Emmanuel Delahaye]

Re: realloc

D² wrote on 21/04/05 :[color=blue]
> I was trying to enlarge the size of an array with this code:
>
> float data [100];[/color]

Bad feeling...
[color=blue]
> data = realloc (data, n*sizeof(float) );[/color]

This is damned wrong. Only an allocated block can be reallocated.
[color=blue]
> but I encountered an error during compile fase,[/color]

Sure. An array is not a modifiable left-value.
[color=blue]
> is this sintax right?[/color]

Nope.
[color=blue]
> How can should I do?[/color]

Try that. Not exactly trivial, but hard to make good and less...

size_t n = 100
float *data = malloc (sizeof *data * n);

if (data != NULL)
{
/* ... */

/* reallocation (say double the size, a common approach) */

{
float *p = realloc (data, sizeof *data * n * 2);

if (p != NULL)
{
n *= 2;
data = p;
}
else
{
/* We do have a memory problem... */
n = 0;
free (data), data = NULL;
}
}

if (data != NULL)
{
/* ... */

/* when finished ... */
free (data), data = NULL;
}

}

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

I once asked an expert COBOL programmer, how to
declare local variables in COBOL, the reply was:
"what is a local variable?"