Appending a value to the end of a dynamic array

问题

Well I have been studying a little C this winter break and in my adventures I stumbled upon an issue with a Dynamic Array.

It's a fairly simple program really. What I am trying to do is to create an array that holds the numbers of the Fibonacci series. Here is the code:

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

int dynamic_arry_append(int* arry, int* number, int* size);

int main() {

    int i, n, size = 3, *arry = NULL, fibarr[size];

    printf("Dynamic array, Fibonacci series. \n");
    printf("Capture upto element: ");
    scanf("%d", &n);

    i = 0;
    // passing the first elements
    fibarr[0] = 0;
    fibarr[1] = 1;
    fibarr[2] = 1;

    while ( i < n ) {
        printf("**%d\n",fibarr[0]);
        dynamic_arry_append( arry, &fibarr[0], &size );
        fibarr[0] = fibarr[1];
        fibarr[1] = fibarr[2];
        fibarr[2] = fibarr[1] + fibarr[0];
        i++;
    }

    for ( i = 0 ; i < size ; i++) 
        printf("Element %d of the array: %d.\n", i, arry[i]);

    return 0;
}

int dynamic_arry_append(int* arry, int* number, int* size) {
    int i;

    int bacon = *size; // first name i thought of
    bacon++;
    int *new_addr = realloc(arry, bacon * sizeof(int));

    if( new_addr != NULL ) {
        arry = new_addr;
        arry[bacon-1] = *number;
        // printf for easier debugging, or so i thought
        for ( i = 0 ; i < bacon ; i++ ) 
            printf("%d\t%d\n", i+1, arry[i]);
        printf("\n");
        *size = bacon;
    } else {
        printf("Error (re)allocating memory.");
        exit (1);
    }

    return 0;
}

At least in my mind this works. However, in practice I get funny results:

Dynamic array, Fibonacci series.
Capture upto element: 5
**0 // next fibonacci number
1       5256368
2       5246872
3       1176530273
4       0

**1
1       5256368
2       5246872
3       1768053847
4       977484654
5       1

**1
1       5256368
2       5246872
3       1551066476
4       1919117645
5       1718580079
6       1

**2
1       5256368
2       5246872
3       977484645
4       1852397404
5       1937207140
6       1937339228
7       2

**3
1       5256368
2       5246872
3       1551071087
4       1953724755
5       842231141
6       1700943708
7       977484653
8       3

/* Code::Blocks output */
Process returned -1073741819 (0xC0000005)   execution time : 17.886 s
Press any key to continue.

I am really baffled by this error, and after searching around I found no solution...Can anyone help? Thank you very much.

回答1:

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

int * dynamic_array_append(int * array, int size);

int main() {

    int i, n, size=0, *array = NULL;

    printf("Dynamic array, Fibonacci series. \n");
    printf("Capture upto element: ");
    scanf("%d", &n);

    for (i=0 ; i<n ; i++)
        array = dynamic_array_append(array, i);

    for (i=0 ; i<n ; i++) 
        printf("array[%d] = %d\n", i, array[i]);

    return 0;
}

int * dynamic_array_append(int * array, int size) 
{
    int i;
    int n1, n2;
    int new_size = size + 1;
    int * new_addr = (int *) realloc(array, new_size * (int)sizeof(int));

    if (new_addr == NULL) {
        printf("ERROR: unable to realloc memory \n");
        return NULL;
    }

    if (size == 0 || size == 1) {
        new_addr[size] = size;
        return new_addr;
    }

    n1 = new_addr[size-1];
    n2 = new_addr[size];
    new_addr[new_size-1] = new_addr[new_size-2] + new_addr[new_size-3];

    return new_addr;
}

/*
Output:

Dynamic array, Fibonacci series. 
Capture upto element: 10
array[0] = 0
array[1] = 1
array[2] = 1
array[3] = 2
array[4] = 3
array[5] = 5
array[6] = 8
array[7] = 13
array[8] = 21
array[9] = 34

*/

Points to note:

The newly (re)allocated array should be returned back to main and stored in a pointer-to-int (or) pass pointer-to-pointer-to-int and update it accordingly once after reallocing
The fibarr is not needed. It doesn't solve any problem.
You don't have to pass the size and the number. Just send the size and it will pick the n-1 and n-2 to calculate n.
This is considered to be highly inefficient. Because if you know the n then you can allocate memory for n integers in one shot and calculate the fib series.

回答2:

The problem may be that the arry pointer variable is passed by value to the function dynamic_arry_append. That means, that changes that you make to the arry variable within that function will not be reflected by any variables outside of that function. For example:

int *a = NULL;

someFunc(a);

// a will still be NULL here no matter what someFunc does to it.

回答3:

You should declare your fibarr as a pointer (so name it differently) not an array. And you should pass to your dynamic_arry_append the address of that pointer, like &fibarr. And you should initialize fibarr in your main with calloc. At last you should dynamically update (and keep, and pass) the size of the allocated array.

回答4:

You are not returning the new address of the array... and you are reading/writing not your memory. Run the program with all error messages under debugger and you'll see the problem is in this line:

  dynamic_arry_append( arry, &fibarr[0], &size );

来源：https://stackoverflow.com/questions/8654041/appending-a-value-to-the-end-of-a-dynamic-array

标签

arrays

dynamic-data

realloc