I can't believe I've been trying to work this out for hours now, and I
can't believe I couldn't find someone asking for a similar solution in
the newsgroups. No wonder I hate C so much, and every time I get the
textbooks out end up throwing them against the wall in rage. Thats
been going on for 10 years now.
Anyway, I have:
typedef struct _record {
int age;
} record;
typedef struct _LinkedList {
void *data;
struct _LinkedList *next;
} LinkedList;
I can add items to my linked list, traverse the list etc. However I
CANNOT get the data OUT of the list.
curr_ptr = head;
while ( curr_ptr != NULL ) {
printf ("traverse: this=%p data=%d\n",
curr_ptr, curr_ptr->data->age);
}
This results in the error:
warning: deferencing 'void *' pointer
request for member 'age' in something not a structure or union.
I know I have to cast it or something.... but I just can't figure it
out!
Arrgh!
Doug
Nov 13 '05
52  5633 
Richard Heathfield wrote:
.... snip ...
Better: if( (new_item == malloc(sizeof *new_item)) == NULL) {
which, as well as being quicker to type, needs less maintenance and is
easier to read.
Harumph. Are you sure? :-)
--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!
On 2003-11-17, Floyd Davidson <fl***@barrow.c om> wrote: James Hu <jx*@despammed. com> wrote:On 2003-11-17, Douglas Garstang <do**@pobox.com > wrote:
... Unfortunately after reading your post several times, I still just
don't get it. I can't even visualise pointers to anything in my head,
let alone pointers to pointers.
...
A pointer to a pointer is analagous to a phone number to a voice
mailbox which can only hold a message that is another phone number.
Ahem... a _pointer_ _to_ _a_ _pointer_ is the phone number of directory
assistance.
...
No, that is a pointer to an oracle, for which there is no C analog, so
it is off-topic in comp.lang.c. Please try rec.humor.oracl e.
-- James
CBFalconer wrote: Richard Heathfield wrote:
... snip ...
Better: if( (new_item == malloc(sizeof *new_item)) == NULL) {
which, as well as being quicker to type, needs less maintenance and is
easier to read.
Harumph. Are you sure? :-)
Modulo the first == (which should be = instead), yes, I'm sure. (Oops.)
--
Richard Heathfield : bi****@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton
In <bp**********@h ercules.btinter net.com> Richard Heathfield <do******@addre ss.co.uk.invali d> writes: CBFalconer wrote:
Richard Heathfield wrote:
... snip ...
Better: if( (new_item == malloc(sizeof *new_item)) == NULL) {
which, as well as being quicker to type, needs less maintenance and is
easier to read.
Harumph. Are you sure? :-)
Modulo the first == (which should be = instead), yes, I'm sure. (Oops.)
See, it's much better to always triple check than to rely on silly gadgets
that work only when you're lucky!
Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Richard Heathfield <do******@addre ss.co.uk.invali d> spoke thus: I just use new, rather than new_item (mainly for the apoplexy it causes in
C++ programmers).
Well, whatever flaws may result from doing so are well worth causing
apoplexy in C++ programmers, eh? ;)
--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.
Dan Pop wrote: In <bp**********@h ercules.btinter net.com> Richard Heathfield
<do******@addre ss.co.uk.invali d> writes:
Modulo the first == (which should be = instead), yes, I'm sure. (Oops.)
See, it's much better to always triple check than to rely on silly gadgets
that work only when you're lucky!
I don't /rely/ on what you call silly gadgets. I use the const==var order as
an additional check, because I know I make mistakes of this kind, no matter
how carefully I check. I know you do, too, because you have done so in an
article posted to this group, so please don't get all high and mighty on
me.
In any event, const==var can never catch a mistakenly typed == where = was
meant; its purpose is to catch (where possible) the /opposite/ mistake.
--
Richard Heathfield : bi****@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton
Christopher Benson-Manica wrote: Richard Heathfield <do******@addre ss.co.uk.invali d> spoke thus:
I just use new, rather than new_item (mainly for the apoplexy it causes
in C++ programmers).
Well, whatever flaws may result from doing so are well worth causing
apoplexy in C++ programmers, eh? ;)
Er, flaws? I haven't spotted any yet. Do feel free to share them. :-)
--
Richard Heathfield : bi****@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton
Richard Heathfield <do******@addre ss.co.uk.invali d> wrote in message news:<bp******* ***@titan.btint ernet.com>... Douglas Garstang wrote:
Thanks Richard, well I felt better for literally 5 minutes. Now I've
reached my next stumbling block. I'm trying to make the list functions
generic. I did have something like this in my append function:
int list_append ( LinkedList **list, void *data ) {
LinkedList *new_item;
I just use new, rather than new_item (mainly for the apoplexy it causes in
C++ programmers).
Bzzzt. Not around here you don't! and I'm not even a C++ programmer.
It's generally necessary to port C code to C++.
karl m
On Tue, 18 Nov 2003 16:35:22 -0800, karl malbrain wrote: Richard Heathfield <do******@addre ss.co.uk.invali d> wrote in message news:<bp******* ***@titan.btint ernet.com>... Douglas Garstang wrote:
> Thanks Richard, well I felt better for literally 5 minutes. Now I've
> reached my next stumbling block. I'm trying to make the list functions
> generic. I did have something like this in my append function:
>
> int list_append ( LinkedList **list, void *data ) {
>
> LinkedList *new_item;
I just use new, rather than new_item (mainly for the apoplexy it causes in
C++ programmers).
Bzzzt. Not around here you don't! and I'm not even a C++ programmer.
It's generally necessary to port C code to C++.
Why? Did the C compiler stop working?
karl malbrain wrote: Richard Heathfield <do******@addre ss.co.uk.invali d> wrote in message
news:<bp******* ***@titan.btint ernet.com>... Douglas Garstang wrote: >
> LinkedList *new_item;
I just use new, rather than new_item (mainly for the apoplexy it causes
in C++ programmers).
Bzzzt. Not around here you don't!
I see no reason why not.
and I'm not even a C++ programmer.
Irrelevant.
It's generally necessary to port C code to C++.
That has not been my experience. If it ain't broke, don't fix it.
--
Richard Heathfield : bi****@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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