Thread: using malloc & realloc

Hi Everyone!
Is there a way to reduce the number of pointers used in this program using malloc itself.

Code:

#include<stdio.h>
#include<stdlib.h>
int main()
{
int *p,*q,i,*r,*w;
p=(int *)malloc(5*sizeof(int));
printf("Enter the 5 numbers\n");
q=p;
for(i=0;i<5;i++)
{
scanf("%d",p);
p++;
}
p=q;
r=(int *)realloc(q,8*sizeof(int));
w=r;
r+=5;
for(i=0;i<3;i++)
{
scanf("%d",r);
r++;
}
r=w;
for(i=0;i<8;i++)
{
printf("%d\n",*(int *)r);
r++;
}
p=q;
r=w;
free(r);
q=NULL;
w=NULL;
return 0;
}

I was just experimenting with using malloc and realloac on how to access and see if it was reading into the new loaction,so took an example of 5 and 8.That's when I realised the number of pointers required to do this simple operation.

Well if it's a problem, you need to roll up your own functions to do this kind of stuff. If you think about it, a lot of this type of work is part of data structure management. So you need to do adequate planning and decide what functions you need to write. It'll be a lot easier if you can write it once, test, and forget about it.

You could also look for a library for a particular data structure. A lot of code is already written, you just have to find it.

ok.Thanks

hi.
The malloc() is used the create the memory allocation in dynamically.
and the realloc() is used the reallocating the memory for already exitsted memory in dynamically in C language.

Originally Posted by shruthi

Is there a way to reduce the number of pointers used in this program using malloc itself.

You would only need two pointers: One which is always pointing to the start of your array and another "helper" pointer which does all the moving around.
Something like this:

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int *numbers, *temp;
    int i;

    if ((numbers = malloc(5 * sizeof(*numbers))) == NULL)
    {
        fprintf(stderr, "Error allocating memory\n");
        exit(EXIT_FAILURE);
    }

    printf("Enter the 5 numbers\n");
    for(i = 0, temp = numbers; i < 5; i++, temp++)
        scanf("%d", temp);

    temp = realloc(numbers, 8 * sizeof(*numbers));
    if (temp != NULL)
        numbers = temp;
    else
    {
        fprintf(stderr, "Error reallocating memory\n");
        free(numbers);
        exit(EXIT_FAILURE);
    }

    printf("Enter 3 more numbers\n");
    for(i = 0, temp = numbers + 5; i < 3; i++, temp++)
        scanf("%d", temp);

    printf("The numbers: ");
    for(i = 0, temp = numbers; i < 8; i++, temp++)
        printf("%d ", *temp);
    putchar('\n');

    free(numbers);
    return EXIT_SUCCESS;
}

Bye, Andreas

Originally Posted by AndiPersti

You would only need two pointers: One which is always pointing to the start of your array and another "helper" pointer which does all the moving around.
Something like this:

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int *numbers, *temp;
    int i;

    if ((numbers = malloc(5 * sizeof(*numbers))) == NULL)
    {
        fprintf(stderr, "Error allocating memory\n");
        exit(EXIT_FAILURE);
    }

    printf("Enter the 5 numbers\n");
    for(i = 0, temp = numbers; i < 5; i++, temp++)
        scanf("%d", temp);

    temp = realloc(numbers, 8 * sizeof(*numbers));
    if (temp != NULL)
        numbers = temp;
    else
    {
        fprintf(stderr, "Error reallocating memory\n");
        free(numbers);
        exit(EXIT_FAILURE);
    }

    printf("Enter 3 more numbers\n");
    for(i = 0, temp = numbers + 5; i < 3; i++, temp++)
        scanf("%d", temp);

    printf("The numbers: ");
    for(i = 0, temp = numbers; i < 8; i++, temp++)
        printf("%d ", *temp);
    putchar('\n');

    free(numbers);
    return EXIT_SUCCESS;
}

Bye, Andreas

This is great! Thanks