TKey Class Reference

Protected default constructor.

This constructor prevents TKey objects from being constructed directly.

Constructs the characteristics of a descriptor type key.

This constructor should be called by the corresponding derived class constructor that takes the same arguments. Typically, the derived class constructor calls this constructor in its constructor initialization list.

No length value is passed as this is implied by the type of key.

Note that the constructor sets the offset value into the protected data member iKeyOffset.

See also: TKeyCmpText

Constructs the characteristics of a text key.

This constructor should be called by the corresponding derived class constructor that takes the same arguments. Typically, the derived class constructor calls this constructor in its constructor initialization list.

Note that the constructor sets the offset value into the protected data member iKeyOffset.

See also: TKeyCmpText

Constructs the characteristics of a numeric key.

This constructor should be called by the corresponding derived class constructor that takes the same arguments. Typically, the derived class constructor calls this constructor in its constructor initialization list.

No length value is passed as this is implied by the type of key.

Note that the constructor sets the offset value into the protected data member iKeyOffset.

See also: TKeyCmpNumeric

Gets a pointer to the key of a specified array element.

The default implementation raises a USER 35 panic.

The function is called by TKey::Compare() to compare the keys of two elements.

The implementation provided by a derived class must convert the index to a pointer to the key within the corresponding element. The implementation depends on the design of the array but, as general rule, use the index value to get a pointer to the corresponding element and then add the TKey protected data member iKeyOffset to this pointer to get a pointer to the key itself.

By convention, the index value is relative to zero; i.e. a zero value refers to the first element in the array. By this convention, the index can take any value between zero and the number of elements within the array minus one.

The function must also handle the special index value KIndexPtr. When this value is passed, the function should return a pointer to the key within the sample element. A pointer to the sample element is held in the protected data member iPtr and can be set up using SetPtr().

The implementation of this function also assumes that the derived class has a pointer to the array itself or has a function for finding it.

See also: TKey::Compare TKey::SetPtr KIndexPtr

Compares the keys of two array elements.

This function is called by User::BinarySearch() and User::QuickSort().

The position of the elements are identified by the specified index values. The default implementation uses the At() virtual function to convert the index values into pointers to the elements themselves.

The default implementation also uses:

1. the TDesC comparison functions to compare descriptor type keys

2. the Mem functions to compare text type keys

3. numeric comparison for numeric type keys.

See also: User::BinarySearch() User::QuickSort() TDesC Mem

Sets the pointer to a sample element whose key is to be used for comparison.

The element can be in an existing array or it can be located anywhere in addressable memory.

The At() member function supplied by a derived class must return a pointer to this sample element's key when passed an index value of KIndexPtr.

SetPtr() must be called before calling User::BinarySearch() because this algorithm uses the key of this sample element as the basis for searching the array.