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how to define this complex declaration and how to use it

Hi,

how can be the declaration of

a pointer which points to dynamic array of pointers and each pointer
from this array points to an dynamic array of pointers which points to
character strings

p-->p-->p
p
p-->p
p
p
p-->p
p
p
p

How to use such storage to fill the strings and then retrieve. Does
anybody has the example
upto this deep pointing algorithm.

Thanks,

Cric

Sep 5 '07 #1
6 1639
On Tue, 04 Sep 2007 21:08:45 -0700, Cric wrote:
Hi,

how can be the declaration of

a pointer which points to dynamic array of pointers and each pointer
from this array points to an dynamic array of pointers which points to
character strings
Usually you'd better have a pointer to the first element of an
array than to the whole array, especially if its size is unknown
at compile time. So you want a pointer to pointer to char, or
pointer to pointer to pointer to char, depending on what you mean
by "points to character strings".
So: char **ptr; or char ***ptr.

--
Army1987 (Replace "NOSPAM" with "email")
No-one ever won a game by resigning. -- S. Tartakower
$ cd /pub
$ more beer
Sep 5 '07 #2
Cric <fr*******@yahoo.comwrote:
# Hi,
#
# how can be the declaration of
#
# a pointer which points to dynamic array of pointers and each pointer
# from this array points to an dynamic array of pointers which points to
# character strings

Also known as Iliffe vectors <http://www.google.com/search?q=iliffe+vector>.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
Leave it to the Catholics to destroy existence.
Sep 5 '07 #3
Sorry may be my description is not clear

I want data storage as
------------------------
<first block>

<char string>
<char string>
<char string>
<char string>
....
....<dynamic>
------------------------
<second block>

<char string>
<char string>
<char string>
<char string>
....
....<dynamic>
--------------------------
<Third block>

<char string>
<char string>
<char string>
<char string>
....
....<dynamic>
----------------------------
many more dynamic blocks may be addedd

so how to have this kind of data structure with reference to pointers

Thanks

Cric

Sep 5 '07 #4
On Wed, 05 Sep 2007 05:01:12 -0700, Cric <fr*******@yahoo.comwrote:
>Sorry may be my description is not clear

I want data storage as
------------------------
<first block>

<char string>
<char string>
<char string>
<char string>
...
...<dynamic>
------------------------
Are all of the multiple strings the same size (or the same maximum
size)? Equivalently, given the address of the first string, can I
compute the address of the second without evaluating the actual length
of the string?

If the answer is yes, then you can point to this block of strings
(actually an array of strings) with a pointer to the first string.
char (*p1)[MAX_STRING_SIZE] = malloc(N * sizeof *p1); would allocate
space for N such strings, each occupying an array of MAX_STRING_SIZE.
p1[0] would be the first array, p1[1] the second, etc. p1 can be
reallocated to allow more strings.

If you do this, you need some way to tell when you are at the last
p[i].

You either keep track of the maximum i p[i] is valid for
elsewhere or

You set the last string to a sentinel value, such as
strcpy(p1[N-1],"");

If the strings are not the same size (often called a jagged or ragged
array), then you basically need one pointer for each string. Since
the string sizes vary, the simplest approach is a char* that points to
the start of the string. The obvious solution is a dynamic array of
such pointers. Something along the lines of

char **p2 = malloc(N * sizeof *p2);
p2[0] = &string0;
p2[1] = &string1; ...

You have the same choices as above for determining the number or
strings plus the option of setting p2[N-1] to NULL. p2 can be
reallocated to allow more strings. Furthermore, if any string is also
dynamically allocated, p2[i] can be reallocated as well.

snip second block
><Third block>

<char string>
<char string>
<char string>
<char string>
...
...<dynamic>
----------------------------
many more dynamic blocks may be addedd
Now you have a dynamic number of blocks. You want a dynamic array
where each element is a pointer to a block.

If you chose the p1 approach above, then the pointer to the block has
type char(*)[MAX_STRING_SIZE]. The simplest approach is to change the
definition of p1 to

typedef char (*T1)[MAX_STRING_SIZE];
T1 p1 = malloc ...;

and your pointer for allocating a dynamic array of T1's is

T1 *da1 = malloc(M * sizeof *da1);

On the other hand, if you are a glutton for punishment, you can omit
the typedef and code

char (*da1)(*)[MAX_STRING_SIZE] = malloc ...

If you chose the p2 approach above, the declarations are much simpler.

char ***da2 = malloc(M * sizeof *da2);
Remove del for email
Sep 6 '07 #5
Cric:
how can be the declaration of

a pointer which points to dynamic array of pointers and each pointer
from this array points to an dynamic array of pointers which points to
character strings

Use typedef's if you're brain hurts. Then try to wean yourself off
them.

Work backwards, reading from right to left:

1: character strings = arrays of char = char arr[NUM_1];
2: dynamic array of pointers which points to = char **p = malloc(NUM_2
* sizeof(char*));
3: a pointer which points to a dynamic array of pointer and each
pointer from this array points to:
char ***p = malloc(NUM_3 * sizeof(char**));

Martin

Sep 10 '07 #6
Cric wrote:
>
Hi,

how can be the declaration of

a pointer which points to dynamic array of pointers and each pointer
from this array points to an dynamic array of pointers which points to
character strings

p-->p-->p
p
p-->p
p
p
p-->p
p
p
p

How to use such storage to fill the strings and then retrieve. Does
anybody has the example
upto this deep pointing algorithm.
How do you feel about using a list of lists of pointers to strings
instead?

--
pete
Sep 10 '07 #7

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