Question

I’m nearing the end of an introductory book on c programming called “C programming in easy steps” by Mike McGrath. I think I’ll have a lot more to learn after this book by the looks of things though. Anyways, I’m working with memory allocation and I wrote this demo program, but it errors closed when I try to run it:

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int i, *arr;

    arr = calloc(5, sizeof(int));
    if(arr!=NULL)
    {
        printf("Enter 5 integers, seperated by a space:");
        for(i=0; i<5; i++) scanf("%d", &arr[i]);
        printf("Adding more space...\n");
        arr = realloc(8, sizeof(int));
        printf("Enter 3 more integers seperated by a space:");
        for(i=5; i<8; i++) scanf("%d", &arr[i]);
        printf("Thanks.\nYour 8 entries were: ");
        for(i=0; i<8; i++) printf("%d, ", arr[i]);
        printf("\n");
        free(arr);
        return 0;
        }
    else {printf("!!! INSUFFICIENT MEMORY !!!\n"); return 1; }
}

Warning message:

|13|warning: passing argument 1 of 'realloc' makes pointer from integer without a cast|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\..\..\..\..\include\stdlib.h|365|note: expected 'void *' but argument is of type 'int'|
||=== Build finished: 0 errors, 1 warnings ===|

The resulting compilation asks for 5 integers and prints “Adding more space…” at which point the program terminates, instead of asking for the additional three integers and printing the input.

Any help would be nice. 🙂 Thanks!

Answer 1

You’re not using realloc the way you should:

/* 8 is not valid here. You need to pass the previous pointer. */
arr = realloc(8, sizeof(int));

Try:

tmp = realloc(arr, 8 * sizeof(*arr));
if (NULL != tmp)
    arr = tmp;

As an aside, your program looks really crammed which makes it hard to read. Maybe leave an empty line once in a while ?