how to free this

[copx]

What is the correct way to free arrays allocated like this (from C FAQ):int
**array2 = (int **)malloc(nrows * sizeof(int *));
array2[0] = (int *)malloc(nrows * ncolumns * sizeof(int));
for(i = 1; i < nrows; i++)
array2[i] = array2[0] + i * ncolumns;

[Eric Sosman]

copx wrote:

What is the correct way to free arrays allocated like this (from C FAQ):int
**array2 = (int **)malloc(nrows * sizeof(int *));
array2[0] = (int *)malloc(nrows * ncolumns * sizeof(int));
for(i = 1; i < nrows; i++)
array2[i] = array2[0] + i * ncolumns;

I'm surprised to see those unnecessary casts in a FAQ
answer. <checks Strange: they're not there in the FAQ.
Where do you suppose they came from?

Anyhow:

free(array2[0]);
free(array2);

The general rule is "One malloc, one free" (with suitable
alterations if you use calloc and/or realloc).

--
Er*********@sun.com

[copx]

"Eric Sosman" <Er*********@sun.comschrieb im Newsbeitrag
news:1199742719.546282@news1nwk...

copx wrote:

>What is the correct way to free arrays allocated like this (from C
FAQ):int **array2 = (int **)malloc(nrows * sizeof(int *));
array2[0] = (int *)malloc(nrows * ncolumns * sizeof(int));
for(i = 1; i < nrows; i++)
array2[i] = array2[0] + i * ncolumns;

I'm surprised to see those unnecessary casts in a FAQ
answer. <checks Strange: they're not there in the FAQ.
Where do you suppose they came from?

They were in the version of the FAQ I read. The first google hit for CLC FAQ
is:
http://docs.mandragor.org/files/Prog.../C/clc_faq_en/

See here:
http://docs.mandragor.org/files/Prog...faq/q6.16.html

Anyhow:

free(array2[0]);
free(array2);

The general rule is "One malloc, one free" (with suitable
alterations if you use calloc and/or realloc).

I know, but the pointer arithmetic (which I almost never use myself) scared
me, so I asked just to be sure.

[Al Balmer]

On Tue, 8 Jan 2008 00:36:22 +0100, "copx" <co**@gazeta.plwrote:

>
"Eric Sosman" <Er*********@sun.comschrieb im Newsbeitrag
news:1199742719.546282@news1nwk...

>copx wrote:

>>What is the correct way to free arrays allocated like this (from C
FAQ):int **array2 = (int **)malloc(nrows * sizeof(int *));
array2[0] = (int *)malloc(nrows * ncolumns * sizeof(int));
for(i = 1; i < nrows; i++)
array2[i] = array2[0] + i * ncolumns;

I'm surprised to see those unnecessary casts in a FAQ
answer. <checks Strange: they're not there in the FAQ.
Where do you suppose they came from?

They were in the version of the FAQ I read. The first google hit for CLC FAQ
is:
http://docs.mandragor.org/files/Prog.../C/clc_faq_en/

See here:
http://docs.mandragor.org/files/Prog...faq/q6.16.html

Dunno what this is. I suggest you use the official one:
http://c-faq.com/
--
Al Balmer
Sun City, AZ

[vippstar]

On Jan 8, 2:05 am, Al Balmer <[e-mail]:

On Tue, 8 Jan 2008 00:36:22 +0100, "copx" <[e-mail]:

"Eric Sosman" <[e-mail] im Newsbeitrag
news:1199742719.546282@news1nwk...

copx wrote:
What is the correct way to free arrays allocated like this (from C
FAQ):int **array2 = (int **)malloc(nrows * sizeof(int *));
array2[0] = (int *)malloc(nrows * ncolumns * sizeof(int));
for(i = 1; i < nrows; i++)
array2[i] = array2[0] + i * ncolumns;

I'm surprised to see those unnecessary casts in a FAQ
answer. <checks Strange: they're not there in the FAQ.
Where do you suppose they came from?

They were in the version of the FAQ I read. The first google hit for CLC FAQ
is:
http://docs.mandragor.org/files/Prog.../C/clc_faq_en/

See here:
http://docs.mandragor.org/files/Prog.../clc_faq_en/C-...

Dunno what this is. I suggest you use the official one:http://c-faq.com/

It is mr Summits personal home page (or, at least it appears to be
so), he clearly states that this very version is out of date, and
suggests to use <http://c-faq.com/instead.

[Keith Thompson]

"copx" <co**@gazeta.plwrites:
[...]

They were in the version of the FAQ I read. The first google hit for CLC FAQ
is:
http://docs.mandragor.org/files/Prog.../C/clc_faq_en/

[...]

That's surprising. A first hit for "comp.lang.c FAQ" is the correct
site, <http://c-faq.com/(also accessible with the usual "www."
prefix if you prefer).

<http://docs.mandragor.org/files/Programming_languages/C/clc_faq_en/>
purports to be "Steve Summit's home page", but it appears to be just a
copy of it, and quite probably an unauthorized one. His actual home
page is <http://www.eskimo.com/~scs/(in which context reference to
"The ISP hosting this page" makes a lot more sense). I'll drop Steve
a line and let him know about this.

--
Keith Thompson (The_Other_Keith) <ks***@mib.org>
[...]
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Richard Heathfield]

vi******@gmail.com said:

On Jan 8, 2:05 am, Al Balmer <[e-mail]:

>On Tue, 8 Jan 2008 00:36:22 +0100, "copx" <[e-mail]:

<snip>

>The first google hit for CLC FAQ is:
http://docs.mandragor.org/files/Prog.../C/clc_faq_en/

....which just demonstrates that you shouldn't always take the first hit as
gospel truth.

>>

>See here:

http://docs.mandragor.org/files/Prog.../clc_faq_en/C-...

>>
Dunno what this is. I suggest you use the official one:http://c-faq.com/

It is mr Summits personal home page (or, at least it appears to be
so),

Steve's home page is certainly not mandragor.org; it is
http://www.eskimo.com/~scs/ - and has been since at least 1999 and
probably long before.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Flash Gordon]

Keith Thompson wrote, On 08/01/08 07:56:

<snip mandragor.org>

page is <http://www.eskimo.com/~scs/(in which context reference to
"The ISP hosting this page" makes a lot more sense). I'll drop Steve
a line and let him know about this.

We went round this buoy April last year, something you might want to
remind Steve of.
http://groups.google.com/group/comp....8bbc02a261d372

My opinion is that the owner of mandragor.org does not care about being
either honest or accurate.
--
Flash Gordon

[Flash Gordon]

Keith Thompson wrote, On 08/01/08 07:56:

<snip>

<http://docs.mandragor.org/files/Programming_languages/C/clc_faq_en/>
purports to be "Steve Summit's home page", but it appears to be just a
copy of it, and quite probably an unauthorized one. His actual home
page is <http://www.eskimo.com/~scs/(in which context reference to
"The ISP hosting this page" makes a lot more sense). I'll drop Steve
a line and let him know about this.

I managed to contact the owner of mandragor.org and he has taken Steve's
home page and the FAQ down now, so we should have a bit less confusion.
I don't know if it was abuse@, postmaster@, the contact address he gave
or the technical contacts his whois records provided that reached him,
but something did.
--
Flash Gordon