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  • 1 Post By AndiPersti

using malloc & realloc

This is a discussion on using malloc & realloc within the C Programming forums, part of the General Programming Boards category; Hi Everyone! Is there a way to reduce the number of pointers used in this program using malloc itself. Code: ...

  1. #1
    Registered User shruthi's Avatar
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    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;
    }
    


  2. #2
    Registered User whiteflags's Avatar
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    You could allocate 8 integers instead of only 5 and stop dicking around with realloc(), unless you're meant to show some competency with that function.

    If you are, you have a potential leak. Here's how you handle it:

    Code:
    int *q = realloc( p, newSize * sizeof( *p ) );
    if ( q != NULL ) { 
       p = q;
    }
    else {
       free( p );
       p = NULL;
    }
    Last edited by whiteflags; 09-11-2012 at 05:45 AM.

  3. #3
    Registered User shruthi's Avatar
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    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.

  4. #4
    Registered User whiteflags's Avatar
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    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.
    shruthi likes this.

  5. #5
    Registered User shruthi's Avatar
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    ok.Thanks

  6. #6
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    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.

  7. #7
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    Quote Originally Posted by shruthi View Post
    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
    shruthi likes this.

  8. #8
    Registered User shruthi's Avatar
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    Quote Originally Posted by AndiPersti View Post
    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

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