Collections: Choosing a Collection Class

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This article contains detailed information designed to help you choose a collection class for your particular application needs.

Your choice of a collection class depends on a number of factors, including:

The features of the class shape: order, indexing, and performance, as shown in the Collection Shape Features table later in this topic
Whether the class uses C++ templates
Whether the elements stored in the collection can be serialized
Whether the elements stored in the collection can be dumped for diagnostics
Whether the collection is type-safe

The following table, Collection Shape Features, summarizes the characteristics of the available collection shapes.

Columns 2 and 3 describe each shape’s ordering and access characteristics. In the table, the term “ordered” means that the order in which items are inserted and deleted determines their order in the collection; it does not mean the items are sorted on their contents. The term “indexed” means that the items in the collection can be retrieved by an integer index, much like items in a typical array.
Columns 4 and 5 describe each shape’s performance. In applications that require many insertions into the collection, insertion speed might be especially important; for other applications, lookup speed may be more important.
Column 6 describes whether each shape allows duplicate elements.

Collection Shape Features

Shape	Ordered?	Indexed?	Insert an element	Search for specified element	Duplicate elements?
List	Yes	No	Fast	Slow	Yes
Array	Yes	By int	Slow	Slow	Yes
Map	No	By key	Fast	Fast	No (keys) Yes (values)

The following table, Characteristics of MFC Collection Classes, summarizes other important characteristics of specific MFC collection classes as a guide to selection. Your choice may depend on whether the class is based on C++ templates, whether its elements can be serialized via MFC’s document serialization mechanism, whether its elements can be dumped via MFC’s diagnostic dumping mechanism, or whether the class is type-safe — that is, whether you can guarantee the type of elements stored in and retrieved from a collection based on the class.

Characteristics of MFC Collection Classes

Class	Uses C++ templates	Can be serialized	Can be dumped	Is type-safe
CArray	Yes	Yes ¹	Yes ¹	No
CByteArray	No	Yes	Yes	Yes ³
CDWordArray	No	Yes	Yes	Yes ³
CList	Yes	Yes ¹	Yes ¹	No
CMap	Yes	Yes ¹	Yes ¹	No
CMapPtrToPtr	No	No	Yes	No
CMapPtrToWord	No	No	Yes	No
CMapStringToOb	No	Yes	Yes	No
CMapStringToPtr	No	No	Yes	No
CMapStringToString	No	Yes	Yes	Yes ³
CMapWordToOb	No	Yes	Yes	No
CMapWordToPtr	No	No	Yes	No
CObArray	No	Yes	Yes	No
CObList	No	Yes	Yes	No
CPtrArray	No	No	Yes	No
CPtrList	No	No	Yes	No
CStringArray	No	Yes	Yes	Yes ³
CStringList	No	Yes	Yes	Yes ³
CTypedPtrArray	Yes	Depends ²	Yes	Yes
CTypedPtrList	Yes	Depends ²	Yes	Yes
CTypedPtrMap	Yes	Depends ²	Yes	Yes
CUIntArray	No	No	Yes	Yes ³
CWordArray	No	Yes	Yes	Yes ³

1. To serialize, you must explicitly call the collection object’s Serialize function; to dump, you must explicitly call its Dump function. You cannot use the form ar << collObj to serialize or the form dmp << collObj to dump.

2. Serializability depends on the underlying collection type. For example, if a typed pointer array is based on CObArray, it is serializable; if based on CPtrArray, it is not serializable. In general, the “Ptr” classes cannot be serialized.

3. If marked Yes in this column, a nontemplate collection class is type-safe provided you use it as intended. For example, if you store bytes in a CByteArray, the array is type-safe. But if you use it to store characters, its type safety is less certain.