How to allocate and deallocate heap memory for 2D array?

Question

I\'m used to PHP, but I\'m starting to learn C. I\'m trying to create a program that reads a file line by line and stores each line to an array.

So far I have a prog

Answer 1

There's no standard resizable array type in C. You have to implement it yourself, or use a third-party library. Here's a simple bare-bones example:

typedef struct int_array
{
    int *array;
    size_t length;
    size_t capacity;
} int_array;

void int_array_init(int_array *array)
{
    array->array = NULL;
    array->length = 0;
    array->capacity = 0;
}

void int_array_free(int_array *array)
{
    free(array->array);
    array->array = NULL;
    array->length = 0;
    array->capacity = 0;
}

void int_array_push_back(int_array *array, int value)
{
    if(array->length == array->capacity)
    {
        // Not enough space, reallocate.  Also, watch out for overflow.
        int new_capacity = array->capacity * 2;
        if(new_capacity > array->capacity && new_capacity < SIZE_T_MAX / sizeof(int))
        {
            int *new_array = realloc(array->array, new_capacity * sizeof(int));
            if(new_array != NULL)
            {
               array->array = new_array;
               array->capacity = new_capacity;
            }
            else
                ; // Handle out-of-memory
        }
        else
            ; // Handle overflow error
    }

    // Now that we have space, add the value to the array
    array->array[array->length] = value;
    array->length++;
}

Use it like this:

int_array a;
int_array_init(&a);

int i;
for(i = 0; i < 10; i++)
    int_array_push_back(&a, i);
for(i = 0; i < a.length; i++)
    printf("a[%d] = %d\n", i, a.array[i]);

int_array_free(&a);

Of course, this is only for an array of ints. Since C doesn't have templates, you'd have to either put all of this code in a macro for each different type of array (or use a different preprocessor such as GNU m4). Or, you could use a generic array container that either used void* pointers (requiring all array elements to be malloc'ed) or opaque memory blobs, which would require a cast with every element access and a memcpy for every element get/set.

In any case, it's not pretty. Two-dimensional arrays are even uglier.