prob with int**

[the consiglieri]

hello there ..
im not much an expert in C....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5 so plzif any body
could help me

[Nick Keighley]

Re: prob with int**

On Sep 21, 12:16 pm, the consiglieri <graciahell...@ gmail.comwrote:

                      im not much an expert in C.....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5  so plzif any body
could help me

Post your code, we can't mind read.
Post in standard english. Nether "...." not "plzif" are standard
english.


--
Nick Keighley

[Flash Gordon]

Re: prob with int**

the consiglieri wrote, On 21/09/08 12:16:

hello there ..
im not much an expert in C....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5 so plzif any body
could help me

There is an error on line 42. If I'm wrong try reading the comp.lang.c
FAQ at http://c-faq.com/ probably starting with section 6, but also 4
and 5. If you still can't fix it and the problem is not on line 42 post
a small compilable example that demonstrates the problem. After all,
without seeing your code all we can do is guess!
--
Flash Gordon
If spamming me sent it to smap@spam.cause way.com
If emailing me use my reply-to address
See the comp.lang.c Wiki hosted by me at http://clc-wiki.net/

[Bartc]

Re: prob with int**


"the consiglieri" <graciahellboy@ gmail.comwrote in message
news:8acdc55c-4f44-4bff-8a2a-c66c48f3033b@d7 7g2000hsb.googl egroups.com...

hello there ..
im not much an expert in C....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5 so plzif any body
could help me

int** requires that you manually allocate memory, which for a 2D array has
to be done in a structured form; have you done so?

--
Bartc

[Malcolm McLean]

Re: prob with int**


"the consiglieri" <graciahellboy@ gmail.comwrote in message

hello there ..
im not much an expert in C....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5 so plzif any body
could help me
>

Hetre's how to do it.

remember to #include stdlib.h

int **mtx;

mtx = malloc(height * sizeof(int *));
if(!mtx)
/* out of memory error, handle here */
for(i=0;i<heigh t;i++)
{
mtx[i] = malloc(width * sizeof(int));
if(!mtx[i])
/* out of memory, handle here */
}

/* ( initialise to zero) */
for(i=0;i,heigh t;i++)
for(ii=0;ii<wid th;ii++)
mxt[i][ii] = 0;


--
Free games and programming goodies.

http://www.personal.leeds.ac.uk/~bgy1mm

[Barry Schwarz]

Re: prob with int**

On Sun, 21 Sep 2008 16:54:48 +0100, "Malcolm McLean"
<regniztar@btin ternet.comwrote :

>
>"the consiglieri" <graciahellboy@ gmail.comwrote in message

>hello there ..
> im not much an expert in C....im trying to use
>int** for reperesentation of matrices(as double subscripted
>arrays .)but at run time an error occurs ..saying ...general exception
>error ...processor fault ....im using TURBO C v4.5 so plzif any body
>could help me
>>

>
>Hetre's how to do it.
>
>remember to #include stdlib.h
>
>int **mtx;
>
>mtx = malloc(height * sizeof(int *));
>if(!mtx)
/* out of memory error, handle here */
>for(i=0;i<heig ht;i++)
>{
mtx[i] = malloc(width * sizeof(int));
if(!mtx[i])
/* out of memory, handle here */
>}
>
>/* ( initialise to zero) */
>for(i=0;i,heig ht;i++)

Obvious finger check. s/i,/i<

for(ii=0;ii<wid th;ii++)
mxt[i][ii] = 0;

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[jameskuyper@verizon.net]

Re: prob with int**

Bartc wrote:

"the consiglieri" <graciahellboy@ gmail.comwrote in message
news:8acdc55c-4f44-4bff-8a2a-c66c48f3033b@d7 7g2000hsb.googl egroups.com...

hello there ..
im not much an expert in C....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5 so plzif any body
could help me

>
int** requires that you manually allocate memory, which for a 2D array has
to be done in a structured form; have you done so?

I'm not sure what you mean by "manually allocate" and "structured ".
Does the following code qualify?:

int row1[] = {1,2,3};
int row2[] = {-6,-5,-4};
int *rows[] = {row1, row2};
int **array = rows;

[Bartc]

Re: prob with int**


"Malcolm McLean" <regniztar@btin ternet.comwrote in message
news:N-ydnZm37YzV80vVR VnyhAA@bt.com.. .

>
"the consiglieri" <graciahellboy@ gmail.comwrote in message

>hello there ..
> im not much an expert in C....im trying to use
>int** for reperesentation of matrices(as double subscripted
>arrays .)but at run time an error occurs ..saying ...general exception
>error ...processor fault ....im using TURBO C v4.5 so plzif any body
>could help me

int **mtx;
>
mtx = malloc(height * sizeof(int *));
if(!mtx)
/* out of memory error, handle here */
for(i=0;i<heigh t;i++)
{
mtx[i] = malloc(width * sizeof(int));
if(!mtx[i])
/* out of memory, handle here */
}
>
/* ( initialise to zero) */
for(i=0;i,heigh t;i++)
for(ii=0;ii<wid th;ii++)
mxt[i][ii] = 0;

This is fiddly enough to be put into it's own function. Here's my code in
bad C. As written it requires the matrix to be indexed as [y][x] rather than
than [x][y] (but it's so long since I've had to subscript a matrix that I
can't remember the form).

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

typedef int T; /* matrix element type */

T** allocmatrix(int rows, int columns) {
T **p;
int i;

if (rows<=0 || columns <=0) return NULL;

p=malloc(sizeof (T*)*rows);
if (p==NULL) return NULL;

for (i=0; i<rows; ++i) {
p[i]=malloc(sizeof( T)*columns);
if (p[i]==NULL) {
/* possibly free already allocated rows here, and p */
return NULL;
}
memset(p[i],0,sizeof(T)*co lumns);
}

return p;
}

void freematrix(T** p, int rows){
int i;

for (i=0; i<rows; ++i)
free(p[i]);

free(p);
}

int main(void){
#define rows 8
#define columns 12
T **mat;
int x,y;

mat=allocmatrix (rows,columns);

if (mat==NULL) exit(0);

for (y=0; y<rows; ++y)
for (x=0; x<columns; ++x)
mat[y][x]=y*1000+x;

for (y=0; y<rows; ++y) {
for (x=0; x<columns; ++x)
printf("%04d ",mat[y][x]);
puts("");
}

freematrix(mat, rows);

}

--
Bartc

[Bartc]

Re: prob with int**


<jameskuyper@ve rizon.netwrote in message
news:3b3914fb-4114-49f2-8f7f-ae6828442741@p2 5g2000hsf.googl egroups.com...

Bartc wrote:

>"the consiglieri" <graciahellboy@ gmail.comwrote in message
>news:8acdc55 c-4f44-4bff-8a2a-c66c48f3033b@d7 7g2000hsb.googl egroups.com...

hello there ..
im not much an expert in C....im trying to use
int** for reperesentation of matrices(as double subscripted
arrays .)but at run time an error occurs ..saying ...general exception
error ...processor fault ....im using TURBO C v4.5 so plzif any body
could help me

>>
>int** requires that you manually allocate memory, which for a 2D array
>has
>to be done in a structured form; have you done so?

>
I'm not sure what you mean by "manually allocate"

Use malloc explicitly.

>and "structured ".

Make use of a row of pointers. See my other post for example.

Does the following code qualify?:
>
int row1[] = {1,2,3};
int row2[] = {-6,-5,-4};
int *rows[] = {row1, row2};
int **array = rows;

This is structured. But not manually allocated using malloc. I'm assuming
the matrix size is a variable (or is large) otherwise you can just declare a
regular matrix:

int matrix[6][9];

--
bartc

[Malcolm McLean]

Re: prob with int**


"Bartc" <bc@freeuk.comw rote in message

I'm assuming
the matrix size is a variable (or is large) otherwise you can just declare
a
regular matrix:
>
int matrix[6][9];
>

2D arrays have all sorts of problems. Firstly they cannot be resized.
Secondly the syntax for passing them to other functions is so complex as to
be effectively unusable. Thirdly the subroutines have to be written to take
fixed-width matrices.
Arrays of pointer, whilst not ideal, get around many of these problems.

My favoured solution is to just allocate a flat buffer and calculate the
offset

matrix[y*height+x] = val;


--
Free games and programming goodies.

http://www.personal.leeds.ac.uk/~bgy1mm

[Flash Gordon]

Re: prob with int**

Malcolm McLean wrote, On 21/09/08 16:54:

>
"the consiglieri" <graciahellboy@ gmail.comwrote in message

>hello there ..
> im not much an expert in C....im trying to use
>int** for reperesentation of matrices(as double subscripted
>arrays .)but at run time an error occurs ..saying ...general exception
>error ...processor fault ....im using TURBO C v4.5 so plzif any body
>could help me
>>

>
Hetre's how to do it.

Well, it is *one* way to do it, but not the only way. The comp.lang.c
FAQ has more methods at hrrp://c-faq.com/

remember to #include stdlib.h
>
int **mtx;
>
mtx = malloc(height * sizeof(int *));

Better would be
mtx = malloc(height * sizeof *mtx);

if(!mtx)
/* out of memory error, handle here */

Note that the out of memory handler needs to stop it from executing the
code below.

for(i=0;i<heigh t;i++)
{
mtx[i] = malloc(width * sizeof(int));

<snip>

Here it would be better to have
mtx[i] = malloc(width * sizeof *mtx[1]);

Note the how many times Malcolm had to get the type right compared to
how many times I need to.

Also depending on what you are trying to do it could be the wrong way.
--
Flash Gordon
If spamming me sent it to smap@spam.cause way.com
If emailing me use my reply-to address
See the comp.lang.c Wiki hosted by me at http://clc-wiki.net/

[Bartc]

Re: prob with int**


"Malcolm McLean" <regniztar@btin ternet.comwrote in message
news:a7udnVznct _pFEvVnZ2dnUVZ8 t7inZ2d@bt.com. ..

>
"Bartc" <bc@freeuk.comw rote in message

>I'm assuming
>the matrix size is a variable (or is large) otherwise you can just
>declare a
>regular matrix:
>>
>int matrix[6][9];
>>

2D arrays have all sorts of problems. Firstly they cannot be resized.
Secondly the syntax for passing them to other functions is so complex as
to be effectively unusable. Thirdly the subroutines have to be written to
take fixed-width matrices.
Arrays of pointer, whilst not ideal, get around many of these problems.
>
My favoured solution is to just allocate a flat buffer and calculate the
offset
>
matrix[y*height+x] = val;

Don't you mean, y*width?

And to pass this to a function still requires this extra parameter, and
possibly height too, depending on what the function does.

(You also have the nuisance of having this extra value: height or width,
associated with each matrix access, and the overhead of an extra multiply.)

--
Bartc

[Malcolm McLean]

Re: prob with int**


"Bartc" <bc@freeuk.comw rote in message news

>
"Malcolm McLean" <regniztar@btin ternet.comwrote in message
news:a7udnVznct _pFEvVnZ2dnUVZ8 t7inZ2d@bt.com. ..

>>
>"Bartc" <bc@freeuk.comw rote in message

>>I'm assuming
>>the matrix size is a variable (or is large) otherwise you can just
>>declare a
>>regular matrix:
>>>
>>int matrix[6][9];
>>>

>2D arrays have all sorts of problems. Firstly they cannot be resized.
>Secondly the syntax for passing them to other functions is so complex as
>to be effectively unusable. Thirdly the subroutines have to be written to
>take fixed-width matrices.
>Arrays of pointer, whilst not ideal, get around many of these problems.
>>
>My favoured solution is to just allocate a flat buffer and calculate the
>offset
>>
>matrix[y*height+x] = val;

>
Don't you mean, y*width?
>
And to pass this to a function still requires this extra parameter, and
possibly height too, depending on what the function does.
>
(You also have the nuisance of having this extra value: height or width,
associated with each matrix access, and the overhead of an extra
multiply.)
>

Yes I do, which is the disadvantage of the manaul method. It's too easy to
make that type of slip.
The multiplication overhead is a type of micro-optimisation. Whilst there
are circumstances where it can make or break a routine, generally that's
what you worry about after you have a nice functioning program. Sometimes
there is a hidden multiply in a 2D array access, though I admit it is easier
for the compiler to optiise out the constant.

--
Free games and programming goodies.

http://www.personal.leeds.ac.uk/~bgy1mm

[Ben Bacarisse]

Re: prob with int**

"Malcolm McLean" <regniztar@btin ternet.comwrite s:

"Bartc" <bc@freeuk.comw rote in message

>I'm assuming
>the matrix size is a variable (or is large) otherwise you can just
>declare a
>regular matrix:
>>
>int matrix[6][9];
>>

2D arrays have all sorts of problems. Firstly they cannot be
resized.

I think this is a red-herring. Neither can 1D arrays. It is always
going to be a bit fiddly to resize 2D arrays in C no matter what
method you use to implement them and your suggestion does not make it
any easier than the "natural" way (see below).

Secondly the syntax for passing them to other functions is so
complex as to be effectively unusable.

No so in C99, and a temporary typedef can be used to make even the
allocation be neat and simple:

int main(int argc, char **argv)
{
size_t n = argc 1 ? atoi(argv[1]) : 4;
size_t m = argc 2 ? atoi(argv[2]) : 5;
typedef double Array[n][m];
Array *ap = malloc(sizeof *ap);
fill(n, m, *ap);
print(n, m, *ap);
return 0;
}

How hard is that? It looks logical and consistent. The function
prototypes are not obscure either[1]:

void fill(size_t n, size_t m, double array[n][m]);
void print(size_t n, size_t m, double array[n][m]);

Thirdly the subroutines have to
be written to take fixed-width matrices.

Again, not in C99. Now I know that C99 is not as portable as C90 but I
think it deserves a fair hearing. This is one thing it does
reasonable well. The fill function might just be:

void fill(size_t n, size_t m, double array[n][m])
{
for (size_t r = 0; r < n; r++)
for (size_t c = 0; c < n; c++)
array[r][c] = (r + 1) * (c + 1);
}

When doing numerical work with arrays in C, C99's features deserve
serious consideration.

To the OP: do consider using C99 if it is available to you.

[1] The form using * is rather less obvious until you think of it is
simply a way to say "some parameter -- the name does not matter":

void fill(size_t, size_t, double array[*][*]);

--
Ben.

[Barry Schwarz]

Re: prob with int**

On Sun, 21 Sep 2008 18:50:44 +0100, "Malcolm McLean"
<regniztar@btin ternet.comwrote :

>
>"Bartc" <bc@freeuk.comw rote in message

>I'm assuming
>the matrix size is a variable (or is large) otherwise you can just declare
>a
>regular matrix:
>>
>int matrix[6][9];
>>

>2D arrays have all sorts of problems. Firstly they cannot be resized.

Isn't the same true for 1D arrays?

>Secondly the syntax for passing them to other functions is so complex as to

You really consider
int func(int x[][9]){...}
to be too complex to use?

>be effectively unusable. Thirdly the subroutines have to be written to take
>fixed-width matrices.
>Arrays of pointer, whilst not ideal, get around many of these problems.
>
>My favoured solution is to just allocate a flat buffer and calculate the
>offset
>
>matrix[y*height+x] = val;

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