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Sequence


Category: containers 
Component type: concept 
Description
A Sequence is a variablesized Container whose
elements are arranged in a strict linear order. It supports insertion
and removal of elements.
Refinement of
Forward Container, Default Constructible
Associated types
None, except for those of Forward Container.
Notation
X

A type that is a model of Sequence

a, b

Object of type X

T

The value type of X

t

Object of type T

p, q

Object of type X::iterator

n

Object of a type convertible to X::size_type

Definitions
If a is a Sequence, then p is a
valid iterator in a if it is a valid (nonsingular) iterator that is
reachable from a.begin().
If a is a Sequence, then [p, q) is a valid range in a
if p and q are valid iterators in a and if q is reachable
from p.
Valid expressions
In addition to the expressions defined in Forward Container, the
following expressions must be valid.
Name

Expression

Type requirements

Return type

Fill constructor

X(n, t)


X

Fill constructor

X a(n, t);



Default fill constructor

X(n)

T is DefaultConstructible.

X

Default fill constructor

X a(n);

T is DefaultConstructible.


Range constructor

X(i, j)

i and j are Input Iterators whose value type is convertible
to T [1]

X

Range constructor

X a(i, j);

i and j are Input Iterators whose value type is convertible
to T [1]


Front

a.front()


reference if a is mutable, const_reference otherwise.

Insert

a.insert(p, t)


X::iterator

Fill insert

a.insert(p, n, t)

a is mutable

void

Range insert

a.insert(p, i, j)

i and j are Input Iterators whose value type is convertible
to T [1]. a is mutable

void

Erase

a.erase(p)

a is mutable

iterator

Range erase

a.erase(p,q)

a is mutable

iterator

Clear

a.clear()

a is mutable

void

Resize

a.resize(n, t)

a is mutable

void

Resize

a.resize(n)

a is mutable

void

Expression semantics
Semantics of an expression is defined only where it is not defined in
Forward Container, or where it differs.
Name

Expression

Precondition

Semantics

Postcondition

Fill constructor

X(n, t)

n >= 0

Creates a sequence with n copies of t

size() == n. Every element is a copy of t.

Fill constructor

X a(n, t);

n >= 0

Creates a sequence with n copies of t

a.size() == n. Every element of a is a copy of t.

Default fill constructor

X(n)

n >= 0

Creates a sequence of n elements initialized to a default value.

size() == n. Every element is a copy of T().

Default fill constructor

X a(n, t);

n >= 0

Creates a sequence with n elements initialized to a default value.

a.size() == n. Every element of a is a copy of T().

Default constructor

X a; or X()


Equivalent to X(0).

size() == 0.

Range constructor

X(i, j)

[i,j) is a valid range.

Creates a sequence that is a copy of the range [i,j)

size() is equal to the distance from i to j. Each element
is a copy of the corresponding element in the
range [i,j).

Range constructor

X a(i, j);

[i,j) is a valid range.

Creates a sequence that is a copy of the range [i,j)

a.size() is equal to the distance from i to j. Each element
in a is a copy of the corresponding element in the
range [i,j).

Front

a.front()

!a.empty()

Equivalent to *(a.first())


Insert

a.insert(p, t)

p is a valid iterator in a. a.size() < a.max_size()

A copy of t is inserted before p. [2] [3]

a.size() is incremented by 1. *(a.insert(p,t)) is a copy of t.
The relative order of elements already in the sequence is unchanged.

Fill insert

a.insert(p, n, t)

p is a valid iterator in a. n >= 0 && a.size() + n <= a.max_size().

n copies of t are inserted before p. [2] [3] [4]

a.size() is incremented by n. The relative order of elements
already in the sequence is unchanged.

Range insert

a.insert(p, i, j)

[i,j) is a valid range. a.size() plus the distance from i to
j does not exceed a.max_size().

Inserts a copy of the range [i,j) before p. [1] [2] [3]

a.size() is incremented by the distance from i to j.
The relative order of elements already in the sequence is unchanged.

Erase

a.erase(p)

p is a dereferenceable iterator in a.

Destroys the element pointed to by p and removes it from a. [3]

a.size() is decremented by 1. The relative order of the other
elements in the sequence is unchanged. The return value is an iterator
to the element immediately following the one that was erased.

Range erase

a.erase(p,q)

[p,q) is a valid range in a.

Destroys the elements in the range [p,q) and removes them from
a. [3]

a.size() is decremented by the distance from i to j.
The relative order of the other elements in the sequence is unchanged.
The return value is an iterator to the element immediately
following the ones that were erased.

Clear

a.clear()


Equivalent to a.erase(a.begin(), a.end())


Resize

a.resize(n, t)

n <= a.max_size()

Modifies the container so that it has exactly n elements, inserting
elements at the end or erasing elements from the end if necessary.
If any elements are inserted, they are copies of t. If n > a.size(),
this expression is equivalent to a.insert(a.end(), n  size(), t).
If n < a.size(), it is equivalent to a.erase(a.begin() + n, a.end()).

a.size() == n

Resize

a.resize(n)

n <= a.max_size()

Equivalent to a.resize(n, T()).

a.size() == n

Complexity guarantees
The fill constructor, default fill
constructor, and range constructor are linear.
Front is amortized constant time.
Fill insert, range insert, and range erase are linear.
The complexities of singleelement insert and erase are sequence
dependent.
Invariants
Models
Notes
[1]
At present (early 1998), not all compilers support
"member templates". If your compiler supports member
templates then i and j may be of any type that
conforms to the Input Iterator
requirements. If your compiler does not yet support member
templates, however, then i and j must be of type
const T* or of type X::const_iterator.
[2]
Note that p equal to a.begin() means to insert
something at the beginning of a (that is, before any elements
already in a), and p equal to a.end() means
to append something to the end of a.
[3]
Warning: there is no guarantee that a valid iterator on
a is still valid after an insertion or an erasure. In some
cases iterators do remain valid, and in other cases they do not. The
details are different for each sequence class.
[4]
a.insert(p, n, t) is guaranteed to be no slower then calling
a.insert(p, t) n times. In some cases it is significantly
faster.
[5]
Vector is usually preferable to
deque and list.
Deque is useful in the case of frequent
insertions at both the beginning and end of the sequence, and
list and slist are useful in the case of frequent insertions
in the middle of the sequence. In almost all other situations,
vector is more efficient.
See also
Container,
Forward Container,
Associative Container,
Front Insertion Sequence,
Back Insertion Sequence,
vector,
deque,
list,
slist
Copyright ©
1999 Silicon Graphics, Inc. All Rights Reserved.
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