CMap Class

Article
01/08/2013

A dictionary collection class that maps unique keys to values.

template< class KEY, class ARG_KEY, class VALUE, class ARG_VALUE >class CMap : public CObject

Parameters

KEY
Class of the object used as the key to the map.
ARG _ KEY
Data type used for KEY arguments; usually a reference to KEY.
VALUE
Class of the object stored in the map.
ARG _ VALUE
Data type used for VALUE arguments; usually a reference to VALUE.

Members

Public Structures

Name	Description
CMap::CPair	A nested structure containing a key value and the value of the associated object.

Public Constructors

Name	Description
CMap::CMap	Constructs a collection that maps keys to values.

Public Methods

Name	Description
CMap::GetCount	Returns the number of elements in this map.
CMap::GetHashTableSize	Returns the number of elements in the hash table.
CMap::GetNextAssoc	Gets the next element for iterating.
CMap::GetSize	Returns the number of elements in this map.
CMap::GetStartPosition	Returns the position of the first element.
CMap::InitHashTable	Initializes the hash table and specifies its size.
CMap::IsEmpty	Tests for the empty-map condition (no elements).
CMap::Lookup	Looks up the value mapped to a given key.
CMap::PGetFirstAssoc	Returns a pointer to the first element.
CMap::PGetNextAssoc	Gets a pointer to the next element for iterating.
CMap::PLookup	Returns a pointer to a key whose value matches the specified value.
CMap::RemoveAll	Removes all the elements from this map.
CMap::RemoveKey	Removes an element specified by a key.
CMap::SetAt	Inserts an element into the map; replaces an existing element if a matching key is found.

Public Operators

Name	Description
CMap::operator [ ]	Inserts an element into the map — operator substitution for SetAt.

Remarks

Once you have inserted a key-value pair (element) into the map, you can efficiently retrieve or delete the pair using the key to access it. You can also iterate over all the elements in the map.

A variable of type POSITION is used for alternate access to entries. You can use a POSITION to "remember" an entry and to iterate through the map. You might think that this iteration is sequential by key value; it is not. The sequence of retrieved elements is indeterminate.

Certain member functions of this class call global helper functions that must be customized for most uses of the CMap class. See Collection Class Helpers in the Macros and Globals section of the MFCReference.

CMap overrides CObject::Serialize to support serialization and dumping of its elements. If a map is stored to an archive using Serialize, each map element is serialized in turn. The default implementation of the SerializeElements helper function does a bitwise write. For information about serialization of pointer collection items derived from CObject or other user defined types, see How to: Make a Type-Safe Collection.

If you need a diagnostic dump of the individual elements in the map (the keys and values), you must set the depth of the dump context to 1 or greater.

When a CMap object is deleted, or when its elements are removed, the keys and values both are removed.

Map class derivation is similar to list derivation. See the article Collections for an illustration of the derivation of a special-purpose list class.

Inheritance Hierarchy

CObject

CMap

Requirements

Header: afxtempl.h