I would like to create a matrix[i][j] of integers by allocating memory
dynamically (malloc or calloc) because i and j are defined during
execution of the program.
I have got not problem to do this in the static way. For instance, if I
want to declare a matrix 20x10 of integers and then to access
matrix[15,8] element:
int matrix[20][10];
int a;
a=matrix[15][8];
But I havn't the clue to do it dynamically in case of i=20 and j=10.
int i,j,a;
i=20;j=10;
Thanks for your help,
Gattaca
Nov 14 '05
14  3134 
Case <no@no.no> wrote: BTW, the FAQ (Q6.16) does use a cast:
int **array1 = (int **)malloc(nrows * sizeof(int *));
Why do you think there should be none?
For several reasons. There have been near endless threads about this on
c.l.c over the past years. I'm sure you can find some of them in a
Usenet archive. Let me just present my favourite argument: by adding a
cast to malloc(), which does not need it at all and is pretty common in
C code, you train yourself to think "Oh, yet another cast. Yawn." Then,
when you encounter a _real_ cast, in a situation where it is needed, you
do not, as you should, sit up and pay attention, because something odd
is done to the C type system; you are used to casts doing, in essence,
nothing, when you _should_ consider a cast to be a warning sign. IOW, a
programmer who casts malloc() is like the little boy who cried "Wolf!".
Richard
Richard Bos wrote: Case <no@no.no> wrote:
BTW, the FAQ (Q6.16) does use a cast:
int **array1 = (int **)malloc(nrows * sizeof(int *));
Why do you think there should be none?
For several reasons. There have been near endless threads about this on
c.l.c over the past years. I'm sure you can find some of them in a
Usenet archive. Let me just present my favourite argument: by adding a
cast to malloc(), which does not need it at all and is pretty common in
C code, you train yourself to think "Oh, yet another cast. Yawn." Then,
when you encounter a _real_ cast, in a situation where it is needed, you
do not, as you should, sit up and pay attention, because something odd
is done to the C type system; you are used to casts doing, in essence,
nothing, when you _should_ consider a cast to be a warning sign. IOW, a
programmer who casts malloc() is like the little boy who cried "Wolf!".
I never knew that K&R are both little boys. ;-) I see malloc() casts
all over their famous book. At page 167 they even say:
"The pointer returned by malloc or calloc has the proper
alignment for the object in question, but it *must* be
cast into the appropriate type, as in ..."
Why the heck is this? And was the FAQ written by other little boys?
Case
Richard Bos wrote: Case <no@no.no> wrote:
BTW, the FAQ (Q6.16) does use a cast:
int **array1 = (int **)malloc(nrows * sizeof(int *));
Why do you think there should be none?
For several reasons. There have been near endless threads about this on
c.l.c over the past years. I'm sure you can find some of them in a
Usenet archive.
I'll try to find some later. Thanks!
Case wrote: I never knew that K&R are both little boys. ;-) I see malloc() casts
all over their famous book. At page 167 they even say:
"The pointer returned by malloc or calloc has the proper
alignment for the object in question, but it *must* be
cast into the appropriate type, as in ..."
From Ritchie's on-line errata list:
142(§6.5, toward the end): The remark about casting the return value of
malloc ("the proper method is to declare ... then explicitly coerce")
needs to be rewritten. The example is correct and works, but the advice
is debatable in the context of the 1988-1989 ANSI/ISO standards. It's
not necessary (given that coercion of void * to ALMOSTANYTYPE * is
automatic), and possibly harmful if malloc, or a proxy for it, fails to
be declared as returning void *. The explicit cast can cover up an
unintended error. On the other hand, pre-ANSI, the cast was necessary,
and it is in C++ also. http://cm.bell-labs.com/cm/cs/cbook/2ediffs.html
Brian Rodenborn
On Mon, 24 May 2004 13:33:50 +0200, Case <no@no.no> wrote:
<snipped casting (return from) malloc> BTW, the FAQ (Q6.16) does use a cast:
Not in the latest version, ca 1999 (!), which the web version at http://www.eskimo.com/~scs/C-faq/top.html (still!) is NOT.
See the download/plaintext versions there under versions.html,
periodically posted, and at rtfm.mit.edu and faqs.org.
- David.Thompson1 at worldnet.att.ne t This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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