ResizeArray

Files:	ResizeArray.h, ResizeArray.c
Derived from:	none
Global instance (if any):	none
Used in optional component:	Part of main VMD code

Description

A template class which implements a dynamically-growing, automatically resizing array of data of a given type. Elements in the array may be accessed via the [] operator. When new data is added to the end of an array, the size of the array is automatically increased if necessary.

A ResizeArray has two sizes that are important:

• The internal size, which is currently allocated size of the array. This is almost always larger than the total number of items stored in the array. A larger-than-necessary buffer is kept so that data may be easily put at the end of the array without having to always reallocate and copy the existing array storage.

• The external size, which is the largest index in the array which has been accessed by the user (either by reading from that index, or writing a value at that index. This is what the user would consider the `size' of the array.

Constructors

• ResizeArray::ResizeArray(int = 10, float = 2.0)
  The first argument is the initial internal size of the array, i.e. the initial number of elements for which to allocate memory (although the initial external size of the array will be zero). The second argument is the resizing factor: when an element of the array beyond the size the internal array is accessed, the array will be made larger by multiplying the current internal size by the rescaling factor. This must be larger than 1.

Internal data structures

• T *data - the current array of data, which will be made larger as the array grows.

• int sz - the internal size of the array.

• float resizeFactor - factor by which the number of elements in data is increased when the array grows too large. sz will be made larger by sz *= resizeFactor.

• int currSize - the external size of the array, that is, the largest index into data which has been accessed. This is always less than or equal to sz.

Nonvirtual member functions

• int num(void) - return the external size of the array.

• T& item(int N) - return (as an lvalue) the Nth item in the array. If N is larger than the internal size of the array, the size of the array will be automatically increased by the current resize factor.

• T& operator[](int N) - same as item, just a nicer form (this really makes it look like a regular array. In fact, you can have 2D and 3D resizing arrays by using this operator, and declaring a template of a template).

• int append(const T&) - append the given data at the end of the array, resizing it if necessary. Returns the index of the item.

• int insert_after(int, const T&) - inserts the given data in the location following the given index. If the given index is less than 0, this puts the item at the beginning of the array. If the given index is larger than the external size, this puts the item at the end of the array. Returns the index of the item.

• int insert_before(int, const T&) - inserts the given data in the location just before the given index. If the given index is less than 0, this puts the item at the beginning of the array. If the given index is larger than the external size, this puts the item at the end of the array. Returns the index of the item.

• void remove(int M= -1, int N= -1) - removes the items with index M ... N, with all items in array positions below this region moved up to fill the resulting hole. If both arguments are negative, this removes ALL the array items. If the second argument is negative, only item M is removed.

• int find(const T&) - scans the array for an element which matches the given argument, and returns the index of the first matching item found. If no match is found, this returns -1.

Method of use

A ResizeArray is created by specifying the type of data to store, i.e.

ResizeArray<char *> stringArray;

Once created, it looks just like an array, and you can use the [] operator to get and set data. For example:

stringArray[3] = "Some text.";

or

cout « stringArray[3] « endl;