Insert to a dynamic array of strings in C

Question

I'm trying to implement a dynamic array of strings. However I encountered a slight problem. I don't allocate the memory properly, but I have no idea what am doing wrong.

My structure for the dynamic array looks like:

typedef struct Array {
    char **ids;
    int size;
} dynamicArray;

I initialize it with:

void initArray(dynamicArray *array) {
    array = malloc(sizeof(dynamicArray));
    array->ids = NULL;
    array->size = 0;
}

Deallocate by:

void freeArray(dynamicArray *array) {
    if (array->size != 0) {
        for (int i = 0; i < array->size; i++) {
            free(array->ids[i]);
        }
        array->size = 0;
        array->ids = NULL;
    }
}

But now the real problem for me is inserting:

void insertArray(dynamicArray *array, char *name) {
    if (array == NULL) {
        return;
    }
    int length = strlen(name) + 1;
    array = realloc(array, (??));
    strcpy(array->ids[array->size++], name);
}

The program fails on the reallocation with: Exception has occurred.. I'm really not sure, what am I doing wrong. I know I should be also allocating the array of string, but have no idea how to put it in there. Could you guys please send me any hints??

If initArray() is supposed to allocate the dynamicArray structure, see stackoverflow.com/questions/13431108/…. If you're calling it with the address of an existing struct, then it shouldn't call malloc(). — Barmar
– Barmar, Commented Nov 30, 2020 at 23:03
I have dynamicArray array; followed by initArray(&array); — Andula
– Andula, Commented Nov 30, 2020 at 23:07
And that variable is declared dynamicArray array;? Then you don't need to call malloc(), the memory is already in the variable. — Barmar
– Barmar, Commented Nov 30, 2020 at 23:09

Barmar · Accepted Answer · 2020-11-30 23:19:20Z

2

The pointer that you need to reallocate is array->ids, not array. When you insert into the array you increase its size. Then the new element points to a copy of the name string.

void insertArray(dynamicArray *array, char *name) {
    if (array == NULL) {
        return;
    }
    int length = strlen(name) + 1;
    char *copy = malloc(length);
    if (copy == NULL) { // malloc failed
        return;
    }
    strcpy(copy, name);
    char **new_ids = realloc(array->ids, (array->size+1) * sizeof(char *));
    if (new_ids == NULL) { // realloc failed
        return;
    }
    array->ids = new_ids;
    array->ids[array->size++] = copy;
}

answered Nov 30, 2020 at 23:19

Barmar

789k57 gold badges554 silver badges669 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Andula Over a year ago

Thank you very much, it works just fine now.

Collectives™ on Stack Overflow

Insert to a dynamic array of strings in C

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related