CODEWITHSUNDEEP
arraysdynamicmemory-managementada
thim
thim

Reputation: 595

Ada - Dynamically reallocate array

I'm trying to write a stack based on array, that can be dynamically reallocated. The main problem I have is how to implement procedure that resizes the array. In C++ it could look like that:

template<class T, int incr>
void Vector<T, incr>::inflate(int increase) {
    const int tsz = sizeof(T*);
    T** st = new T*[quantity + increase];
    memset(st, 0, (quantity + increase) * tsz);
    memcpy(st, storage, quantity * tsz);
    quantity += increase;
    delete []storage;
    storage = st;
}

where int quantity; and T** storage; are declared in private section.

If there is anyone who could share me some sample I'd be much grateful. I tried to look through the implementation of Ada.Containers.Vectors but argh... it's to big =P

So far I've made this Vector.ads Can anyone help?

Upvotes: 3

Views: 2095

Answers (3)

thim
thim

Reputation: 595

Ok, case is solved. I've finished my Vector class (which is actually a stack build on an array). Thank everyone for help.

Just for posterity here is my code. Hope someone will learn something from it. Code -> https://gist.github.com/496a50bc7f5cd93f8d91

If you'd like to take a look and find something worth changing just comment. ;D

Upvotes: 5

trashgod
trashgod

Reputation: 205775

If you go with Ada.Containers.Vectors, there's a helpful discussion in the Rationale for Ada 2005: §8.2 Lists and vectors. Basically, you instantiate the generic package with your Index_Type and Element_Type:

package Container is new Containers.Vectors (Natural, T);

Then declare a variable having the new type:

Stack : Container.Vector;

The Push procedure then becomes Stack.Append and the Pop function returns Stack.Last_Element. Note the availability of prefixed notation.

Upvotes: 5

Marc C
Marc C

Reputation: 8522

Presumably you know how to initially allocate the (empty) array for your stack.

When you need to reallocate to a larger array, allocate it into a local access variable, akin to "st" in your C++ example. Then loop though the existing, full array, copying its elements into your newly allocated one.

Free, using an instantiation of Unchecked Deallocation, the old array--that's the Elements field in your Vector record. Then set the Elements field to the variable containing the newly allocated array.

Essentially, it closely follows your C++ example, only you don't need to mess around with sizeof() and you use a copy loop instep of memset/memcpy.

Upvotes: 4

Related Questions