Containers

A container is an STL template class that manages a sequence of elements. Such elements can be of any object type that supplies a copy constructor, a destructor, and an assignment operator (all with sensible behavior, of course). The destructor may not throw an exception. This document describes the properties required of all such containers, in terms of a generic template class Container. An actual container template class may have additional template parameters. It will certainly have additional member functions.

The STL template container classes are:

    deque
    hash_map
    hash_multimap
    hash_multiset
    hash_set
    list
    map
    multimap
    multiset
    set
    slist
    vector

The four hash containers and slist are not required by the C++ Standard. The Standard C++ library template class basic_string also meets the requirements for a template container class.

namespace std {
template<class Ty>
    class Container;

        // TEMPLATE FUNCTIONS
template<class Ty>
    bool operator==(
        const Container<Ty>& left,
        const Container<Ty>& right);
template<class Ty>
    bool operator!=(
        const Container<Ty>& left,
        const Container<Ty>& right);
template<class Ty>
    bool operator<(
        const Container<Ty>& left,
        const Container<Ty>& right);
template<class Ty>
    bool operator>(
        const Container<Ty>& left,
        const Container<Ty>& right);
template<class Ty>
    bool operator<=(
        const Container<Ty>& left,
        const Container<Ty>& right);
template<class Ty>
    bool operator>=(
        const Container<Ty>& left,
        const Container<Ty>& right);
template<class Ty>
    void swap(
        Container<Ty>& left,
        Container<Ty>& right);
    };

Container

begin · clear · const_iterator · const_reference · const_reverse_iterator · difference_type · empty · end · erase · iterator · max_size · rbegin · reference · rend · reverse_iterator · size · size_type · swap · value_type

template<class Ty>
    class Container {
public:
    typedef T0 size_type;
    typedef T1 difference_type;
    typedef T2 reference;
    typedef T3 const_reference;
    typedef T4 value_type;
    typedef T5 iterator;
    typedef T6 const_iterator;
    typedef T7 reverse_iterator;
    typedef T8 const_reverse_iterator;
    iterator begin();
    const_iterator begin() const;
    iterator end();
    const_iterator end() const;
    reverse_iterator rbegin();
    const_reverse_iterator rbegin() const;
    reverse_iterator rend();
    const_reverse_iterator rend() const;
    size_type size() const;
    size_type max_size() const;
    bool empty() const;
    iterator erase(iterator where);
    iterator erase(iterator first, iterator last);
    void clear();
    void swap(Container& right);
    };

The template class describes an object that controls a varying-length sequence of elements, typically of type Ty. The sequence is stored in different ways, depending on the actual container.

A container constructor or member function may find occasion to call the constructor Ty(const Ty&) or the function Ty::operator=(const Ty&). If such a call throws an exception, the container object is obliged to maintain its integrity, and to rethrow any exception it catches. You can safely swap, assign to, erase, or destroy a container object after it throws one of these exceptions. In general, however, you cannot otherwise predict the state of the sequence controlled by the container object.

A few additional caveats:

• If the expression ~Ty() throws an exception, the resulting state of the container object is undefined.
• If the container stores an allocator object al, and al throws an exception other than as a result of a call to al.allocate, the resulting state of the container object is undefined.
• If the container stores a function object comp, to determine how to order the controlled sequence, and comp throws an exception of any kind, the resulting state of the container object is undefined.

The container classes defined by STL satisfy several additional requirements, as described in the following paragraphs.

Container template class list provides deterministic, and useful, behavior even in the presence of the exceptions described above. For example, if an exception is thrown during the insertion of one or more elements, the container is left unaltered and the exception is rethrown.

For all the container classes defined by STL, if an exception is thrown during calls to the following member functions:

insert // single element inserted at end
push_back
push_front

the container is left unaltered and the exception is rethrown.

For all the container classes defined by STL, no exception is thrown during calls to the following member functions:

pop_back
pop_front

The member function erase throws an exception only if a copy operation (assignment or copy construction) throws an exception.

Moreover, no exception is thrown while copying an iterator returned by a member function.

The member function swap makes additional promises for all container classes defined by STL:

• The member function throws an exception only if the container stores an allocator object al, and al throws an exception when copied, or if the container stores a function object comp, to determine how to order the controlled sequence, and comp throws an exception when copied.
• References, pointers, and iterators that designate elements of the controlled sequences being swapped remain valid.

An object of a container class defined by STL allocates and frees storage for the sequence it controls through a stored object of type Alloc, which is typically a template parameter. Such an allocator object must have the same external interface as an object of class allocator<Ty>. In particular, Alloc must be the same type as Alloc::rebind<value_type>::other

For all container classes defined by STL, the member function:

Alloc get_allocator() const;

returns a copy of the stored allocator object. Note that the stored allocator object is not copied when the container object is assigned. All constructors initialize the value stored in allocator, to Alloc() if the constructor contains no allocator parameter.

According to the C++ Standard a container class defined by STL can assume that:

• All objects of class Alloc compare equal.
• Type Alloc::const_pointer is the same as const Ty *.
• Type Alloc::const_reference is the same as const Ty&.
• Type Alloc::pointer is the same as Ty *.
• Type Alloc::reference is the same as Ty&.

In this implementation, however, containers do not make such simplifying assumptions. Thus, they work properly with allocator objects that are more ambitious:

• All objects of class Alloc need not compare equal. (You can maintain multiple pools of storage.)
• Type Alloc::const_pointer need not be the same as const Ty *. (A const pointer can be a class.)
• Type Alloc::pointer need not be the same as Ty *. (A pointer can be a class.)

Container::begin

const_iterator begin() const;
iterator begin();

The member function returns an iterator that points at the first element of the sequence (or just beyond the end of an empty sequence).

Container::clear

void clear();

The member function calls erase( begin(), end()).

Container::const_iterator

typedef T6 const_iterator;

The type describes an object that can serve as a constant iterator for the controlled sequence. It is described here as a synonym for the unspecified type T6.

Container::const_reference

typedef T3 const_reference;

The type describes an object that can serve as a constant reference to an element of the controlled sequence. It is described here as a synonym for the unspecified type T3 (typically Alloc::const_reference).

Container::const_reverse_iterator

typedef T8 const_reverse_iterator;

The type describes an object that can serve as a constant reverse iterator for the controlled sequence. It is described here as a synonym for the unspecified type T8 (typically reverse_iterator <const_iterator>).

Container::difference_type

typedef T1 difference_type;

The signed integer type describes an object that can represent the difference between the addresses of any two elements in the controlled sequence. It is described here as a synonym for the unspecified type T1 (typically Alloc::difference_type).

Container::empty

bool empty() const;

The member function returns true for an empty controlled sequence.

Container::end

const_iterator end() const;
iterator end();

The member function returns an iterator that points just beyond the end of the sequence.

Container::erase

iterator erase(iterator where);
iterator erase(iterator first, iterator last);

The first member function removes the element of the controlled sequence pointed to by where. The second member function removes the elements of the controlled sequence in the range [first, last). Both return an iterator that designates the first element remaining beyond any elements removed, or end() if no such element exists.

The member functions throw an exception only if a copy operation throws an exception.

Container::iterator

typedef T5 iterator;

The type describes an object that can serve as an iterator for the controlled sequence. It is described here as a synonym for the unspecified type T5. An object of type iterator can be cast to an object of type const_iterator.

Container::max_size

size_type max_size() const;

The member function returns the length of the longest sequence that the object can control, in constant time regardless of the length of the controlled sequence.

Container::rbegin

const_reverse_iterator rbegin() const;
reverse_iterator rbegin();

The member function returns a reverse iterator that designates the last element of the controlled sequence. Hence, it designates the beginning of the reverse sequence.

Container::reference

typedef T2 reference;

The type describes an object that can serve as a reference to an element of the controlled sequence. It is described here as a synonym for the unspecified type T2 (typically Alloc::reference). An object of type reference can be cast to an object of type const_reference.

Container::rend

const_reverse_iterator rend() const;
reverse_iterator rend();

The member function returns a reverse iterator that designates the (fictitious) element before the first element of the controlled sequence. Hence, it points just beyond the end of the reverse sequence.

Container::reverse_iterator

typedef T7 reverse_iterator;

The type describes an object that can serve as a reverse iterator for the controlled sequence. It is described here as a synonym for the unspecified type T7 (typically reverse_iterator <iterator>).

Container::size

size_type size() const;

The member function returns the length of the controlled sequence, in constant time regardless of the length of the controlled sequence.

Container::size_type

typedef T0 size_type;

The unsigned integer type describes an object that can represent the length of any controlled sequence. It is described here as a synonym for the unspecified type T0 (typically Alloc::size_type).

Container::swap

void swap(Container& right);

The member function swaps the controlled sequences between *this and right. If get_allocator() == right.get_allocator(), it does so in constant time. Otherwise, it performs a number of element assignments and constructor calls proportional to the number of elements in the two controlled sequences.

Container::value_type

typedef T4 value_type;

The type is a synonym for the template parameter Ty. It is described here as a synonym for the unspecified type T4 (typically Alloc::value_type).

operator!=

template<class Ty>
    bool operator!=(
        const Container <Ty>& left,
        const Container <Ty>& right);

The template function returns !(left == right).

operator==

template<class Ty>
    bool operator==(
        const Container <Ty>& left,
        const Container <Ty>& right);

The template function overloads operator== to compare two objects of template class Container. The function returns left.size() == right.size() && equal(left. begin(), left. end(), right.begin()).

operator<

template<class Ty>
    bool operator<(
        const Container <Ty>& left,
        const Container <Ty>& right);

The template function overloads operator< to compare two objects of template class Container. The function returns lexicographical_compare(left. begin(), left. end(), right.begin(), right.end()).

operator<=

template<class Ty>
    bool operator<=(
        const Container <Ty>& left,
        const Container <Ty>& right);

The template function returns !(right < left).

operator>

template<class Ty>
    bool operator>(
        const Container <Ty>& left,
        const Container <Ty>& right);

The template function returns right < left.

operator>=

template<class Ty>
    bool operator>=(
        const Container <Ty>& left,
        const Container <Ty>& right);

The template function returns !(left < right).

swap

template<class Ty>
    void swap(
        Container <Ty>& left,
        Container <Ty>& right);

The template function executes left.swap(right).

See also the Table of Contents and the Index.

Copyright © 1994-2002 by P.J. Plauger. Portions derived from work copyright © 1994 by Hewlett-Packard Company. All rights reserved.