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The vector, forward_list, list, deque, and array template classes are all sequence containers, and they all have the methods listed previously, with the exception that forward_list isn’t reversible and doesn’t support the methods of Table G.3. A sequence container, not surprisingly, holds a homogeneous set of items in linear order. If the sequence has a fixed number of elements, array is the usual choice. Otherwise, vector, which combines the random access of array with the ability to add and delete items should be your first recourse. However, if there are frequent additions in the middle of the sequence, consider using list or forward_list. And if additions and deletions primarily occur at the two ends of the sequence, consider deque.

The fixed size of an array object prevents array from using many of the sequence methods. Table G.5 lists additional methods available for sequence containers other than array. (forward_list has somewhat different definitions for resize().) Again, X is a container type, such as vector, and T is the type stored in the container, such as int. a is a value of type X. t is an lvalue or const rvalue of type X::value_type. rv is a non-const rvalue of that same type. i and j are input iterators. [i, j) is a valid range. il is an object of type initializer_list. p is a valid const iterator to a. q is a valid dereferenceable const iterator to a. [q1,q2) is a valid range of const iterators. n is an integer of X::size_type. Args is a template parameter pack, and args is a function parameter pack with the pattern Args&&.

Table G.5. Additional Operations Defined for Sequence Containers

Table G.6 lists methods common to some of the sequence classes (vector, forward_list, list, and deque).

Table G.6. Operations Defined for Some Sequences

The vector template additionally has the methods in Table G.7. Here, a is a vector container and n is an integer of X::size_type.

Table G.7. Additional Operations for Vectors

The list template additionally has the methods in Table G.8. Here, a and b are list containers, and T is the type stored in the list, such as int, t is a value of type T, i and j are input iterators, q2 and p are iterators, q and q1 are dereferenceable iterators, and n is an integer of X::size_type. The table uses the standard STL notation [i, j), meaning the range from i up to, but not including, j.

Table G.8. Additional Operations for Lists

The forward-list operations are similar. However, because a forward_list template class iterator can’t go backwards, some methods have to be adjusted. Thus, the insert(), erase(), and splice() methods are replaced with the insert_after(), erase_after(), and splice_after() methods, all of which operate on the position following an iterator position rather than preceding it.

Additional Operations for Sets and Maps

Associative containers, of which sets and maps are models, have a Key template parameter and a Compare template parameter, which indicate, respectively, the type of the key used to order the contents and the function object, termed a comparison object, used to compare key values. For the set and multiset containers, the stored keys are the stored values, so the key type is the same as the value type. For the map and multimap containers, the stored values of one type (template parameter T) are associated with a key type (template parameter Key), and the value type is pair. Associative containers have additional members to describe these features, as listed in Table G.9.

Table G.9. Types Defined for Associative Containers