char (*name)[3]
David Michael Schwartz
char (*name)[3]
I think it is an array of pointers to char yet I cannot
get any of the pointers to accept a string.
For example,
*name[0] = " hello ";
does not work.
I've got K&R opened to p.109 and the FAQ opened to 2.12.
woe. For any response, I will be most grateful.
Kurt Watzka
>What is the meaning and use of the following declaration,
>char (*name)[3]
>I think it is an array of pointers to char yet I cannot
>get any of the pointers to accept a string.
It might be a pointer to arrays of three characters?
*After* allocating memory, assign characters to the
elements of name. Treat name as a two-dimensional array
of char.
name = malloc(SIZE*3*sizeof(char));
name[i][2] = 'a';
Kurt Watzka
wat...@statistik.uni-muenchen.d400.de
ua3...@sunmail.lrz-muenchen.de
-------------------------------------
Ray Reid
: What is the meaning and use of the following declaration,
: char (*name)[3]
: For example,
: *name[0] = " hello ";
: does not work.
Depending on your compiler, declare name as following....
char *name[3];
if you want to assign a pointer use,
name[0] = "hello";
Your code was trying to stuff a strings worth of gear into a char.
Kevin D. Quitt
>char (*name)[3]
Get the program cdecl:
cdecl> explain char (*name)[3]
declare name as pointer to array 3 of char
cdecl> declare name as array 3 of pointer to char
char *name[3]
cdecl>
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Jonas Schlein
|>
|> char (*name)[3]
|>
|> I think it is an array of pointers to char yet I cannot
|> get any of the pointers to accept a string.
That's because it's a pointer to an array of three characters. You would
have to allocate space, but after you do that you can dereference it and
use it just like an array of 3 characters.
--
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Vincenzo Romano
>What is the meaning and use of the following declaration,
>char (*name)[3]
>I think it is an array of pointers to char yet I cannot
>get any of the pointers to accept a string.
You're right!
>For example,
>*name[0] = " hello ";
>does not work.
... bacause you made a mistake! If name is a vector of pointers to chars,
name[0] is a pointer to char and *name[0] is the first char pointed by it!
Try:
name[0] = " hello ";
>I've got K&R opened to p.109 and the FAQ opened to 2.12.
>woe. For any response, I will be most grateful.
You're welcome!
--
Vincenzo "Enzo" Romano .--------------------------------------------------.
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mu...@MILES.cnuce.cnr.IT | as Humans. Surely they won't become so stupid. |
vro...@NYX.cs.du.edu `--------------------------------------[ Enzo ]----'
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Vincenzo "Enzo" Romano .--------------------------------------------------.
CNUCE/C.N.R. Pisa | Maybe Computers will never become as intelligent |
mu...@MILES.cnuce.cnr.IT | as Humans. Surely they won't become so stupid. |
vro...@NYX.cs.du.edu `--------------------------------------[ Enzo ]----'
Arjan Kenter
[about what ``char (*name)[3];'' means and why *name[0]="string" doesn't work]
|> Depending on your compiler, declare name as following....
Why should that depend on your compiler? Any compiler that does not
accept it, ought to be thrown out the window rightaway.
|> char *name[3];
|>
|> if you want to assign a pointer use,
|>
|> name[0] = "hello";
|>
|> Your code was trying to stuff a strings worth of gear into a char.
Still, this does not answer the other question: what does char (*name)[3] mean?
C declarations are read "inside out" so that their declaration matches their
use as close as possible. So you first see
*name
which tells you that `name' is a pointer to something. To what then? Well:
char ... [3]
`name' is a pointer to an array of three characters.
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David Anderson
: char (*name)[3]
: For example,
: *name[0] = " hello ";
: does not work.
Quick Answer: 'name' is a pointer to an array of 3 characters.
Long Answer: These types of questions come up from time to time and I have
passed on (via email) my article on using the "clockwise rule". I thought that
I would post it again since it has been a long time since I posted this to this
newsgroup.
The clockwise rule is a method which I use when teaching C to help people learn
how to parse these complicated declarations *in their head*. It is very easy to
use this technique, and I'll guarantee you will never have further problems
understanding C declarations once you learn this technique.
So without further ado... the "clockwise rule":
*********************************************************************************
The "Clockwise/Spiral Rule"
===========================
By David Anderson
-----------------
There is a technique known as the "Clockwise/Spiral Rule" which enables
any C programmer to parse in their head any C declaration!
There are three simple steps to follow:
1. Starting with the unknown element, move in a spiral/clockwise direction;
when ecountering the following elements replace them with the corresponding
english statements:
[X] or [] => Array X size of... or Array undefined size of...
(type1, type2) => function passing type1 and type2 returning...
* => pointer(s) to...
2. Keep doing this in a spiral/clockwise direction until all tokens have been
covered.
3. Always resolve anything in parenthesis first!
Example #1: Simple declaration
+-------+
| +-+ |
| ^ | |
char *str[10];
^ ^ | |
| +---+ |
+-----------+
Question we ask ourselves: What is str?
"str is an...
o We move in a spiral clockwise direction starting with 'str' and the first
character we see is a '[' so, that means we have an array, so...
"str is an array 10 of...
o Continue in a spiral clockwise direction, and the next thing we encounter is
the '*' so, that means we have pointers, so...
"str is an array 10 of pointers to...
o Continue in a spiral direction and we see the end of the line (the ';'), so
keep going and we get to the type 'char', so...
"str is an array 10 of pointers to char"
o We have now "visited" every token; therefore we are done!
Example #2: Pointer to Function declaration
+--------------------+
| +---+ |
| |+-+| |
| |^ || |
char *(*fp)( int, float *);
^ ^ ^ || |
| | +--+| |
| +-----+ |
+------------------------+
Question we ask ourselves: What is fp?
"fp is a...
o Moving in a spiral clockwise direction, the first thing we see is a ')';
therefore, fp is inside parenthesis, so we continue the spiral inside the
parenthesis and the next character seen is the '*', so...
"fp is a pointer to...
o We are now out of the parenthesis and continuing in a spiral clockwise
direction, we see the '('; therefore, we have a function, so...
"fp is a pointer to a function passing an int and a pointer to float
returning...
o Continuing in a spiral fashion, we then see the '*' character, so...
"fp is a pointer to a function passing an int and a pointer to float
returning a pointer to...
o Continuing in a spiral fashion we see the ';', but we haven't visited all
tokens, so we continue and finally get to the type 'char', so...
"fp is a pointer to a function passing an int and a pointer to float
returning a pointer to a char"
Example #3: The "Ultimate"
+-----------------------------+
| +---+ |
| +---+ |+-+| |
| ^ | |^ || |
void (*signal(int, void (*fp)(int)))(int);
^ ^ | ^ ^ || |
| +------+ | +--+| |
| +--------+ |
+----------------------------------+
Question we ask ourselves: What is 'signal'?
Notice that signal is *inside* parenthesis, so we must resolve this first!
o Moving in a *clockwise* direction we see '(' so we have...
"signal is a function passing an int and a...
o Hmmm, we can use this same rule on 'fp', so... What is fp? fp is also inside
parenthesis so continuing we see an '*', so...
"fp is a pointer to...
o Continue in a spiral clockwise direction and we get to '(', so...
"fp is a pointer to a function passing int returning..."
o Now we continue out of the function parenthesis and we see void, so...
"fp is a pointer to a function passing int returning nothing (void)"
o We have finished with fp so let's catch up with 'signal', we now have...
"signal is a function passing an int and a pointer to a function passing an
int returning nothing (void) returning...
o We are still inside parenthesis so the next character seen is a '*', so...
"signal is a function passing an int and a pointer to a function passing an
int returning nothing (void) returning a pointer to...
o We have now resolved the items within parenthesis, so continuing clockwise,
we then see another '(', so...
"signal is a function passing an int and a pointer to a function passing an
int returning nothing (void) returning a pointer to a function passing an
int returning...
o *Finally* we continue and the only thing left is the word 'void', so the
final complete definition for signal is:
"signal is a function passing an int and a pointer to a function passing an
int returning nothing (void) returning a pointer to a function passing an
int returning nothing (void)"
The same rule is applied for const and volatile. For Example:
const char *chptr;
o Now, what is chptr??
"chptr is a pointer to a char constant"
How about this one:
char * const chptr;
o Now, what is chptr??
"chptr is a constant pointer to char"
Finally:
volatile char * const chptr;
o Now, what is chptr??
"chptr is a constant pointer to a char volatile.
Practice this rule with the examples found in K&R II on page 122.
************************************************************************
Copyright (C) 1993,1994 David Anderson
This article may be freely distributed as long as the author's name and
this notice are retained.
************************************************************************
--
David AR Anderson
email: David_A...@Mitel.COM
Mitel Corporation Disclaimer: My opinions are my own!
Klaus Guhr
Bye,
Klaus