OT: C syntax question

2009-06-29 Thread Robert Huff 

Let us suppose I have a structure:

struct CONTINENT {
...
}

I use this to create an array of pointers to said struct:

struct CONTINENT *Asia[10][10];

Now I pass this array to a function:

plate_shift(Asia, (int) foo, (float) bar);

In the definition of the function, I say:

int plate_shift(Cont,f,b)
struct CONTINENT *Cont[10][10];
int f;
float b;
{
...
}

and the compiler does not complain.  If, however, I try to
prototype the function as:

  extern int plate_shift(struct CONTINENT *[][],int,float);

with:

CFLAGS = -Wall -std=c99

I get:

error: array type has incomplete element type

Changing to:

  extern int plate_shift(struct CONTINENT *foo[][],int,float);

returns the same error.
KR 2ed is not helpful, nor is a quick poke around the web.
What am I forgetting?

Respectfully,


Robert Huff

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Re: OT: C syntax question

2009-06-29 Thread Brad Mettee 

At 08:41 PM 6/29/2009, Robert Huff wrote:


Let us suppose I have a structure:

struct CONTINENT {
...
}

I use this to create an array of pointers to said struct:

struct CONTINENT *Asia[10][10];

Now I pass this array to a function:

plate_shift(Asia, (int) foo, (float) bar);

In the definition of the function, I say:

int plate_shift(Cont,f,b)
struct CONTINENT *Cont[10][10];
int f;
float b;
{
...
}

and the compiler does not complain.  If, however, I try to
prototype the function as:

  extern int plate_shift(struct CONTINENT *[][],int,float);

with:

CFLAGS = -Wall -std=c99

I get:

error: array type has incomplete element type

Changing to:

  extern int plate_shift(struct CONTINENT *foo[][],int,float);

returns the same error.
KR 2ed is not helpful, nor is a quick poke around the web.
What am I forgetting?

Respectfully,


Robert Huff


I believe since you are declaring the array as having a fixed number of 
elements, you must declare the function to take it the same way, like this:


  extern int plate_shift(struct CONTINENT *[10][10],int,float);

Without the 10,10 size definition, the plate_shift function would have no 
idea how big the array of pointers actually is.



Brad Mettee
PC HotShots, Inc.
Baltimore, MD
(410) 426-7617

 - Let us bring out the *Power* of your PCs. -
- Custom Business Software Solutions since 1991 -

visit http://www.pchotshots.com for information about our company.

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Re: OT: C syntax question

2009-06-29 Thread Chuck Swiger 

Hi--

On Jun 29, 2009, at 5:41 PM, Robert Huff wrote:

and the compiler does not complain.  If, however, I try to
prototype the function as:

 extern int plate_shift(struct CONTINENT *[][],int,float);

with:

CFLAGS = -Wall -std=c99

I get:

error: array type has incomplete element type


You need to provide the size for all but the first element; see KRv2  
section 5.9 (p 113), or something like:


  http://home.netcom.com/~tjensen/ptr/ch7x.htm

Regards,
--
-Chuck

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Re: OT: C syntax question

2009-06-29 Thread Charlie Kester 

On Mon 29 Jun 2009 at 17:51:37 PDT Brad Mettee wrote:


I believe since you are declaring the array as having a fixed number 
of elements, you must declare the function to take it the same way, 
like this:


 extern int plate_shift(struct CONTINENT *[10][10],int,float);

Without the 10,10 size definition, the plate_shift function would have
no idea how big the array of pointers actually is.



Close.

If you pass a two-dimensional array as an argument, you must specify at
least the number of elements in the minor dimension, so the compiler
will know how to compute, for example, the offset of array[3][0] versus
array[6][0].

So this works:

   extern int plate_shift(struct CONTINENT *[][10], int, float);

But the following doesn't work, because it doesn't tell the compiler how
to compute the offsets:

   extern int plate_shift(struct CONTINENT *[10][], int, float); 


Of course, it doesn't hurt to specify the number of elements in
both dimensions.  But it would be a less general solution,  With
only the minor dimension specified, plate_shift can take pointers
to arrays of 20, 30, 40, 100 or 200 CONTINENT structures.  Any
multiple of 10 will do.  (But then you need to tell plate_shift when
it's reached the last set of pointers, or it might run off the end of
the array.  The usual way to handle this is to use all NULLs in the last
row, as a kind of sentinel.)
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Re: OT: C syntax question

2009-06-29 Thread Charlie Kester 

On Mon 29 Jun 2009 at 19:12:10 PDT Charlie Kester wrote:


Of course, it doesn't hurt to specify the number of elements in
both dimensions.  But it would be a less general solution,  With
only the minor dimension specified, plate_shift can take pointers
to arrays of 20, 30, 40, 100 or 200 CONTINENT structures.  Any


Oops.  That's not worded correctly.  It should be:

... plate_shift can take a pointer to a multidimensional array of
20,30,40, 100 or 200 CONTINENT structures.

(Don't you hate it when your mistakes come back to haunt you in your
inbox?)
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Re: OT: C syntax question

2009-06-29 Thread Charlie Kester 

On Mon 29 Jun 2009 at 19:20:04 PDT Charlie Kester wrote:

On Mon 29 Jun 2009 at 19:12:10 PDT Charlie Kester wrote:


Of course, it doesn't hurt to specify the number of elements in
both dimensions.  But it would be a less general solution,  With
only the minor dimension specified, plate_shift can take pointers
to arrays of 20, 30, 40, 100 or 200 CONTINENT structures.  Any


Oops.  That's not worded correctly.  It should be:

... plate_shift can take a pointer to a multidimensional array of
20,30,40, 100 or 200 CONTINENT structures.

(Don't you hate it when your mistakes come back to haunt you in your
inbox?)


I should have quit while I was ahead.  If this was a programming
interview, I just flunked it.  :(

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Re: OT: C syntax question

2009-06-29 Thread Erich Dollansky 
Hi,

On 30 June 2009 am 10:40:01 Charlie Kester wrote:
 On Mon 29 Jun 2009 at 19:20:04 PDT Charlie Kester wrote:
 
 (Don't you hate it when your mistakes come back to haunt you
  in your inbox?)

at least there is nobody seeing your red face on a mailing list.

 I should have quit while I was ahead.  If this was a
 programming interview, I just flunked it.  :(

I would never get the idea asking a programmer questions like this 
at all.

Erich
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OT: C syntax question

2009-06-29 Thread Robert Huff 

Robert Huff writes:

   Let us suppose I have a structure:

Thanks, everyone - you nailed it in one.


Robert What a _maroon_! Huff

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Re: OT: C syntax question

2009-06-29 Thread Charlie Kester 

On Mon 29 Jun 2009 at 19:48:04 PDT Erich Dollansky wrote:


I would never get the idea asking a programmer questions like this at
all.


Yeah, nowadays nobody asks C programming questions in an interview.
It's all web programming now.  Back in the day, however, I was asked
(and asked) questions much like this one.   I used to have it down cold,
but since I retired my brain cells are forgetting a lot of it.
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