[LCP]Re: 2D arrays:dynamic allocation and freeing

Sun Feb 6 15:38:02 UTC 2005

 hi,

>The way to dynamically allocate a 2D array is :
>int a(*)[5];

should be 'int (*a)[5];'
try 'cdecl' command in linux to verify declarations. 

>1.
>After allocating space for pointers, is it not the
>case that i need to 
>allocate space for the array they are pointing to?,
as >we usually do 
>for a pointer to point to array of elements.

if you want to have a 5*8 array, allocation should be
 a=(int (*)[5])malloc(sizeof (int)*40);

now "a" will be point to an 8 element array, whose
elements are 5 elment array of 'int'.

Thus when you are trying acess a[1][2], u will get 3rd
'int' in 2nd element of array pointed by a.
In another way a[1][2] can also be accessed by 
*((int *)a+7).

>2.
>Is my way of freeing ok

In this case free(a) will do.

vivek  

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--0-2021490201-1107277796=:43222
Content-Type: text/html; charset=us-ascii

<DIV>
<DIV>hi all,<BR><BR>The way to dynamically allocate a
2D array is 
:<BR><BR><BR>int a(*)[5];<BR><BR>a=(int 
(*)[5])malloc(sizeof(int)*5);<BR><BR><BR>This will
create array of pointer to arrays.<BR><BR>We can
access 
elements as a 2D array<BR>a[1][1] with access
particular 
element.<BR><BR><BR><BR>Question:<BR>1.<BR>After
allocating space for pointers, is it 
not the case that i need to allocate space for the
array they are 
pointing to?, as we usually do for a pointer to point
to array of 
elements.<BR><BR>2.<BR>Is my way of freeing 
ok<BR><BR>for(i=0;i&lt;5;i++)<BR>free(a[i]);<BR><BR>Because
it will free the pointers , what about the 
elements associated with those pointers.
<DIV>hi all,<BR><BR>The way to dynamically allocate a
2D array is 
:<BR><BR><BR>int a(*)[5];<BR><BR>a=(int 
(*)[5])malloc(sizeof(int)*5);<BR><BR><BR>This will
create array of pointer to arrays.<BR><BR>We can
access 
elements as a 2D array<BR>a[1][1] with access
particular 
element.<BR><BR><BR><BR>Question:<BR>1.<BR>After
allocating space for pointers, is it 
not the case that i need to allocate space for the
array they are 
pointing to?, as we usually do for a pointer to point
to array of 
elements.<BR><BR>2.<BR>Is my way of freeing 
ok<BR><BR>for(i=0;i&lt;5;i++)<BR>free(a[i]);<BR><BR>Because
it will free the pointers , what about the 
elements associated with those pointers.</DIV><!-- /
message --></DIV><!-- / 
message 
--></DIV><p>__________________________________________________<br>Do
You Yahoo!?<br>Tired of spam?  Yahoo! Mail has the
best spam 
protection around <br>http://mail.yahoo.com 
--0-2021490201-1107277796=:43222--

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