Question about an Array of Varying Arrays

**Lewis11** · 08-25-2015

Hello folks, just a quick question regarding initialising an array to contain other arrays.

The problem I'm encountering is that I want to fill different elements of a large array (called "holder") with a smaller array (called "arr") which changes within each iteration of a loop.

Below kind of what I was thinking of doing;

Code:

int L = 31;
int n = 5;
int* arr;
arr = (int*)malloc(L*sizeof(int));

// Here I need to initialise "holder", but I'm not sure how

for (i = 0; i < n; i++) {
   while (val <= 0) {
       arr = GenerateArray(L);
       val = CalculateVal(arr);
    }
    holder[something][something] = something
}

Filling "arr" and using it as a stand-alone array is fine, but the problems I'm coming across are that I don't know how to initialise "holder", and then I don't know how to properly put "arr" into a cell (or across many?) within it.

Some extra information, not sure if it will help or not.
- "arr" is of length L, a non-constant variable
- L is the first dimension of "holder"
- n is the number of iterations of the loop, and as such the second dimension of "holder"

Any help and advice is appreciated, cheers

**laserlight** · 08-25-2015

I am curious as to how L is supposed to change on each iteration (you did write "array of varying arrays"), or if you actually have a dynamic rectangular 2D array (in which case there may be a more efficient technique available). Anyway, assuming that you are dealing with jagged arrays, one might write along these lines:

Code:

int L = 31;
int n = 5;

int **holder = malloc(n * sizeof(*holder));

if (holder) {
    int *arr;

    for (i = 0; i < n; i++) {
        arr = malloc(L * sizeof(*arr));
        if (arr) {
            while (val <= 0) {
                arr = GenerateArray(L);
                val = CalculateVal(arr);
            }
            holder[i] = arr;
        } else {
            /* handle failure to allocate memory */
        }
    }
} else {
    /* handle failure to allocate memory */
}

Remember to free what you malloc.

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