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Recommendations for Choosing a Collection Class

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.

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