array initializer / conversion to pointer

[Alexander Stippler]

Hello,

I've got a quite simple question. I want to have something like

int
main()
{
double array[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
double **field;
field = array;
}

The compiler complains an not allowed conversion in the assignment
field = array;
It's neccessary that field is of type double**. How to manage an
initialization like the above?

regards,
alex

[Joona I Palaste]

Alexander Stippler <st**@mathemati k.uni-ulm.de> scribbled the following:

Hello, I've got a quite simple question. I want to have something like int
main()
{
double array[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
double **field;
field = array;
} The compiler complains an not allowed conversion in the assignment
field = array;
It's neccessary that field is of type double**. How to manage an
initialization like the above?

Declare field as double (*field)[3] instead.

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Stronger, no. More seductive, cunning, crunchier the Dark Side is."
- Mika P. Nieminen

[Al Bowers]

Alexander Stippler wrote:

Hello,

I've got a quite simple question. I want to have something like

int
main()
{
double array[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
double **field;
field = array;
}

The compiler complains an not allowed conversion in the assignment
field = array;
It's neccessary that field is of type double**. How to manage an
initialization like the above?

This is a faq question and answer. Read faq question 6.18 located:
http://www.eskimo.com/~scs/C-faq/q6.18.html

As the faq suggests, make this:
double (*field)[3] = array;
An example is shown below using in function PrintARRAY, using a
typedef.

If, as you say, it is neccessary that field be type double**, then
you can still do it at the expense of making access to the elements
a little more difficult. This is shown in functions PrintARRAY2 and
PrintARRAY3 below.

#include <stdio.h>

#define ROW 3
#define COL 4

typedef double (*ARR)[COL];

void PrintARRAY(ARR row);
void PrintARRAY2(dou ble **field);
void PrintARRAY3(dou ble **field);

int main(void)
{
double array[ROW][COL] = {{1,2,3,11}, {4,5,6,22}, {7,8,9,33}};
ARR this = array;
double **field = (double **)array;

puts("Using function PrintARRAY");
PrintARRAY(this );
puts("\nUsing function printARRAY2");
PrintARRAY2(fie ld);
puts("\nUsing function printARRAY3");
PrintARRAY3(fie ld);
return 0;
}

void PrintARRAY(ARR row)
{
int i,j;

for(i = 0; i < ROW;i++)
{
for(j = 0; j < COL; j++)
printf("%.2f ",row[i][j]);
putchar('\n');
}
return;
}

void PrintARRAY2(dou ble **field)
{
int i,j;
double (*arr)[COL] = (double (*)[COL])field;

for(i = 0; i < ROW;i++,arr++)
{
for(j = 0; j < COL; j++)
printf("%.2f ",(*arr)[j]);
putchar('\n');
}
return;
}

void PrintARRAY3(dou ble **field)
{
int i,j;
double *arr= (double *)field;

for(i = 0;i < ROW; i++)
{
for(j = 0; j < COL;j++)
printf("%.2f ",arr[i*COL+j]);
putchar('\n');
}
return;
}
--
Al Bowers
Tampa, Fl USA
mailto: xa******@myrapi dsys.com (remove the x to send email)
http://www.geocities.com/abowers822/

[Alexander Stippler]

Joona I Palaste wrote:

Alexander Stippler <st**@mathemati k.uni-ulm.de> scribbled the following:

Hello,

I've got a quite simple question. I want to have something like

int
main()
{
double array[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
double **field;
field = array;
}

The compiler complains an not allowed conversion in the assignment
field = array;
It's neccessary that field is of type double**. How to manage an
initialization like the above?

Declare field as double (*field)[3] instead.

Sorry, but I cannot influence the type of field, as I already mentioned in
my first posting! It is 'external' to my influence. I need it to be
double **, so what?

best regards, alex

[Mark McIntyre]

On Thu, 27 May 2004 15:54:10 +0200, in comp.lang.c , Alexander Stippler
<st**@mathemati k.uni-ulm.de> wrote:

Joona I Palaste wrote:

Alexander Stippler <st**@mathemati k.uni-ulm.de> scribbled the following:

I've got a quite simple question. I want to have something like double array[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
double **field;
field = array; The compiler complains an not allowed conversion in the assignment
field = array;

Declare field as double (*field)[3] instead.

Sorry, but I cannot influence the type of field, as I already mentioned in
my first posting! It is 'external' to my influence. I need it to be
double **, so what?

So then you are in trouble. You can't assign the array to the pointer. You
will have to alloc memory for an intermediate variable of type double**,
point field to it, and copy the data from array into it.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.c om/ms3/bchambless0/welcome_to_clc. html>
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[Leor Zolman]

On Thu, 27 May 2004 09:48:26 -0400, Al Bowers <xa******@rapid sys.com>
wrote:

ARR this = array; .... PrintARRAY(this );

....

this sure jumped out at me. I mean, 'this'.

The most recent post I found Googling for "C++ keywords" was from
1999...I'd wager there have probably been at least /some/ more recent
discussions on this topic, but searching for 'this' probably wouldn't have
been fruitful. So I thought I'd take the opportunity to revisit the topic.

I on general principles avoid using anything I'm aware is a C++ keyword in
C programs. I personally end up compiling lots of code as both C and C++,
so in my case developing that habit was a no-brainer. I suggest, however,
that "better safe than sorry" is a good enough reason for anyone who knows
the keyword conflicts to avoid using C++ keywords in C programs.

That 1999 posting mentioned some counter-arguments, such as "Well, why not
avoid Java and Perl and Python keywords, too?" and "There are enough
porting issues between C and C++ that keyword collisions would be a
relatively minor issue." But I still thing avoiding them would be a Good
Idea on general principles.

Thoughts?
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html

[Dan Pop]

In <4o************ *************** *****@4ax.com> Leor Zolman <le**@bdsoft.co m> writes:

On Thu, 27 May 2004 09:48:26 -0400, Al Bowers <xa******@rapid sys.com>
wrote:

ARR this = array;

...

PrintARRAY(this );

...

this sure jumped out at me. I mean, 'this'.

The most recent post I found Googling for "C++ keywords" was from
1999...I'd wager there have probably been at least /some/ more recent
discussions on this topic, but searching for 'this' probably wouldn't have
been fruitful. So I thought I'd take the opportunity to revisit the topic.

I on general principles avoid using anything I'm aware is a C++ keyword in
C programs. I personally end up compiling lots of code as both C and C++,
so in my case developing that habit was a no-brainer. I suggest, however,
that "better safe than sorry" is a good enough reason for anyone who knows
the keyword conflicts to avoid using C++ keywords in C programs.

Thoughts?

As well written C code seldom qualifies as well written C++ code, too,
there is little point in "porting" C code to C++. Compile it as C code
and link it to the rest of the C++ application: the C++ language provides
explicit support for this approach. In this case, there is no point in
paying *any* attention to the C++ keywords or reserved identifiers.
Paying attention to the C99 reserved identifiers is already a non-trivial
task...

Of course, if the project specification (or the customer) *requires* that
the code is compilable as both C and C++, it must be written in the
common subset of the two languages and this automatically rules out the
usage of any C++ keywords as identifiers. Until now, only P.J. Plauger
claimed that he had to satisfy such customer requirements.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Martin Ambuhl]

Leor Zolman wrote:

I on general principles avoid using anything I'm aware is a C++ keyword in
C programs.

On genereal principles, I avoid any language that steals the common and
useful identifiers "this" and "new".

[Alan Balmer]

On Thu, 27 May 2004 13:16:27 -0400, Martin Ambuhl
<ma*****@earthl ink.net> wrote:

Leor Zolman wrote:

I on general principles avoid using anything I'm aware is a C++ keyword in
C programs.

On genereal principles, I avoid any language that steals the common and
useful identifiers "this" and "new".

I recently had a disagreement with the people at Slickedit, who make
my otherwise favorite editor. They don't distinguish between C and C++
in their syntax recognition. I had a legacy program with a variable
name "class", and it refused to tag it.

--
Al Balmer
Balmer Consulting
re************* ***********@att .net

[Joe Wright]

Alexander Stippler wrote:

Joona I Palaste wrote:

Alexander Stippler <st**@mathemati k.uni-ulm.de> scribbled the following:

Hello,

I've got a quite simple question. I want to have something like

int
main()
{
double array[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
double **field;
field = array;
}

The compiler complains an not allowed conversion in the assignment
field = array;
It's neccessary that field is of type double**. How to manage an
initializati on like the above?

Declare field as double (*field)[3] instead.

Sorry, but I cannot influence the type of field, as I already mentioned in
my first posting! It is 'external' to my influence. I need it to be
double **, so what?

best regards, alex

I've seen some of the advice you've received. The best by far is
'Read the FAQ'. Please do so. You will not be sorry, I promise.

If you're stuck with ..

double **field;

... do this.

#include <stdlib.h>
#define ROW 3
#define COL 3
...
int r, c, d = 0;
...
field = malloc(ROW * sizeof *field);
for (r = 0; r < ROW; ++r)
field[r] = malloc(COL * sizeof **field);

for (r = 0; r < ROW; ++r)
for (c = 0; c < COL; ++c)
field[r][c] = ++d;
--
Joe Wright mailto:jo****** **@comcast.net
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---