C Programming - Memory Allocation - Discussion

Discussion Forum : Memory Allocation - Point Out Correct Statements (Q.No. 1)
1.
Point out the correct statement will let you access the elements of the array using 'p' in the following program?
#include<stdio.h>
#include<stdlib.h>

int main()
{
    int i, j;
    int(*p)[3];
    p = (int(*)[3])malloc(3*sizeof(*p));
    return 0;
}
for(i=0; i<3; i++)
{
    for(j=0; j<3; j++)
        printf("%d", p[i+j]);
}
for(i=0; i<3; i++)
    printf("%d", p[i]);
for(i=0; i<3; i++)
{
    for(j=0; j<3; j++)
        printf("%d", p[i][j]);
}
for(j=0; j<3; j++)
    printf("%d", p[i][j]);
Answer: Option
Explanation:
No answer description is available. Let's discuss.
Discussion:
17 comments Page 2 of 2.

Bhargav said:   1 decade ago
Here type casting and it is array of pointers. So we have to access by using double pointer. So option C p[i][j] is similar to that.

Saksham said:   1 decade ago
@pragya Type casting (int(*)[3]) will not increase the size. So it's just 18 bytes!

Tofik Kacchi said:   1 decade ago
Here initially *p[3] will statically create an array of p[3].

Then again reallocating using malloc will create another array of size 3.

Therefore, its p[3][3].hence we require 2 nested for loop.

Pragya said:   1 decade ago
@ Teju

Yes. It allocates 54 bytes because

sizeof(*p)=6 bytes
So 3 * 6 = 18 bytes

and then int (*)[3] points to an array of 3 blocks each having 18 bytes.

So p = (18 + 18 + 18) = 54 bytes.

Teju said:   1 decade ago
Does

p = (int(*)[3])malloc(3*sizeof(*p));

allocates 54 bytes of memory ? Anyone please explain.

Gopi said:   1 decade ago
Here, int(*p)[3]; //its like p[3]

p = (int(*)[3])malloc(3*sizeof(*p));

and again we are allocating more memory to it so like p[3][3] .

Bhavi said:   1 decade ago
Please give explanation to this program.


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