Allocating space for array of pointers?

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Allocating space for array of pointers?
6 answers - 521 bytes -
If I have this struct:
#include <stdlib.h>
#include <stdio.h>
#define KIDS 4
typedef struct test {
int x;
int y;
} container;
I would now like to make an array containing 4 pointers to this struct. But
I would also like to allocate space for this array:
int main(void)
{
container *new[4];
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!
return 0;
}
Do I have to allocate space for each pointer at a time?
No.1 | | 601 bytes | |
Paminu wrote:
If I have this struct:

#include <stdlib.h>
#include <stdio.h>
#define KIDS 4

typedef struct test {
int x;
int y;
} container;
--
I would now like to make an array containing 4 pointers to this struct. But
I would also like to allocate space for this array:

int main(void)
{
container *new[4];
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!

return 0;
}

And what might that error be? (Looks K to me)

Do I have to allocate space for each pointer at a time?

No.

HTH,
No.2 | | 1221 bytes | |
Artie Gold wrote:

Paminu wrote:
>If I have this struct:
>>
>#include <stdlib.h>
>#include <stdio.h>
>#define KIDS 4
>>
>typedef struct test {
>int x;
>int y;
>} container;
>>
>>
>I would now like to make an array containing 4 pointers to this struct.
>But I would also like to allocate space for this array:
>>
>int main(void)
>{
>container *new[4];
>new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!
>>
>return 0;
>}
>>
>
And what might that error be? (Looks K to me)

test4.c:13: error: incompatible types in assignment

where line 13 contains:
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!

I have instead tried:

container *new[4];
int j;
for (j = 0; j < 4; j++)
{
new[j]=malloc(sizeof(container));
new[j]=NULL;

}

Then I get no error!
No.3 | | 836 bytes | |
Paminu wrote:
If I have this struct:

#include <stdlib.h>
#include <stdio.h>
#define KIDS 4

typedef struct test {
int x;
int y;
} container;
--
I would now like to make an array containing 4 pointers to this struct. But
I would also like to allocate space for this array:

int main(void)
{
container *new[4];
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!

As it should. You have already declared new as an array[4] of pointers
to container.

{
size_t i;
for (i = 0; i < 4; i++)
if (!(new[i] = malloc(sizeof *new[i])))
{ /* handle error */ }
}

return 0;
}

Do I have to allocate space for each pointer at a time?

No, you need to allocate space for what each pointer points to.
No.4 | | 901 bytes | |
Artie Gold wrote:
[]
container *new[4];
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!
[]

And what might that error be? (Looks K to me)

"new" is an array of 4 pointers to "container", not a pointer to an
array of 4 "container"s.

Do I have to allocate space for each pointer at a time?

No.

It depends. If you want "new" to be an array of 4 pointers, then yes:

container *new[4];/* As in the original code. */

/* Allocate each pointer. This can also be in a for-loop */
new[0] = malloc(sizeof(container));
new[1] = malloc(sizeof(container));
new[2] = malloc(sizeof(container));
new[3] = malloc(sizeof(container));

If you want it to point to an array of 4 containers:

container *new;
new = malloc(sizeof(container)*4);

BTW, this is a perfect example of how C++ is not a "superset" of C.
No.5 | | 354 bytes | |
Kenneth Brody wrote:
Artie Gold wrote:
[]

container *new[4];
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!

[]
>
>>And what might that error be? (Looks K to me)
>
course, a ludicrous example of cerebral flatulence on m part
[snip]
No.6 | | 531 bytes | |
Thu, 09 Feb 2006 20:51:30 +0100, in comp.lang.c , Paminu
<sdef@asd.comwrote:

container *new[4];
new=malloc(sizeof(container *) * 4); // THIS LINE GIVES AN ERRR!

>
>test4.c:13: error: incompatible types in assignment

"new" is an array of four pointers. You can't assign directly to the
array.

>I have instead tried:
new[j]=malloc(sizeof(container));

yes, thats ok, because new[j] is a pointer.
Mark McIntyre

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Allocating space for array of pointers?