vector.html

指导程序员合理、高效的进行标准模板库编程。

Creates an empty vector.
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<tt>vector(size_type n)</tt>
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 <A href="Sequence.html">Sequence</A>
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Creates a vector with <tt>n</tt> elements.
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<tt>vector(size_type n, const T&amp; t)</tt>
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 <A href="Sequence.html">Sequence</A>
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Creates a vector with <tt>n</tt> copies of <tt>t</tt>.
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<tt>vector(const vector&amp;)</tt>
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 <A href="Container.html">Container</A>
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The copy constructor.
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<pre>
template &lt;class <A href="InputIterator.html">InputIterator</A>&gt;
vector(InputIterator, InputIterator)
<A href="#1">[1]</A>
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 <A href="Sequence.html">Sequence</A>
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Creates a vector with a copy of a range.
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<tt>~vector()</tt>
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The destructor.
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<tt>vector&amp; operator=(const vector&amp;)</tt>
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The assignment operator
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<tt>void reserve(size_t)</tt>
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<tt>vector</tt>
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See below.
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<tt>reference front()</tt>
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 <A href="Sequence.html">Sequence</A>
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Returns the first element.
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<tt>const_reference front() const</tt>
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 <A href="Sequence.html">Sequence</A>
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Returns the first element.
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<tt>reference back()</tt>
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 <A href="BackInsertionSequence.html">Back Insertion Sequence</A>
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Returns the last element.
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<tt>const_reference back() const</tt>
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 <A href="BackInsertionSequence.html">Back Insertion Sequence</A>
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Returns the last element.
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<tt>void push_back(const T&amp;)</tt>
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 <A href="BackInsertionSequence.html">Back Insertion Sequence</A>
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Inserts a new element at the end.
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<tt>void pop_back()</tt>
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 <A href="BackInsertionSequence.html">Back Insertion Sequence</A>
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Removes the last element.
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<tt>void swap(vector&amp;)</tt>
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 <A href="Container.html">Container</A>
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Swaps the contents of two vectors.
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iterator insert(iterator pos,
                const T&amp; x)
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 <A href="Sequence.html">Sequence</A>
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Inserts <tt>x</tt> before <tt>pos</tt>.
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template &lt;class <A href="InputIterator.html">InputIterator</A>&gt;
void insert(iterator pos,
            InputIterator f, InputIterator l)
<A href="#1">[1]</A>
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 <A href="Sequence.html">Sequence</A>
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Inserts the range <tt>[first, last)</tt> before <tt>pos</tt>.
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<pre>
void insert(iterator pos, 
            size_type n, const T&amp; x)
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 <A href="Sequence.html">Sequence</A>
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Inserts <tt>n</tt> copies of <tt>x</tt> before <tt>pos</tt>.
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<tt>iterator erase(iterator pos)</tt>
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 <A href="Sequence.html">Sequence</A>
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Erases the element at position <tt>pos</tt>.
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<tt>iterator erase(iterator first, iterator last)</tt>
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 <A href="Sequence.html">Sequence</A>
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Erases the range <tt>[first, last)</tt>
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<tt>void clear()</tt>
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 <A href="Sequence.html">Sequence</A>
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Erases all of the elements.
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<pre>
bool operator==(const vector&amp;, 
                const vector&amp;)
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 <A href="ForwardContainer.html">Forward Container</A>
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Tests two vectors for equality.  This is a global function, not
   a member function.
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bool operator&lt;(const vector&amp;, 
               const vector&amp;)
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 <A href="ForwardContainer.html">Forward Container</A>
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Lexicographical comparison.  This is a global function, not
   a member function.
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<h3>New members</h3>
These members are not defined in the 
<A href="RandomAccessContainer.html">Random Access Container</A> 
and <A href="BackInsertionSequence.html">Back Insertion Sequence</A>
requirements, but are specific to <tt>vector</tt>.
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Member
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Description
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<tt>size_type capacity() const</tt>
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Number of elements for which memory has been allocated.
   <tt>capacity()</tt> is always greater than or equal to <tt>size()</tt>.
   <A href="#2">[2]</A> <A href="#3">[3]</A>
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<tt>void reserve(size_type n)</tt>
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If <tt>n</tt> is less than or equal to <tt>capacity()</tt>, this call has no effect.
    Otherwise, it is a request for allocation of additional 
    memory.  If the request is successful, then <tt>capacity()</tt> is
    greater than or equal to <tt>n</tt>; otherwise, <tt>capacity()</tt> is unchanged.
    In either case, <tt>size()</tt> is unchanged.  
    <A href="#2">[2]</A> <A href="#4">[4]</A>
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<h3>Notes</h3>
<P><A name="1">[1]</A>
This member function relies on <i>member template</i> functions, which
at present (early 1998) are not supported by all compilers.  If your
compiler supports member templates, you can call this function with
any type of <A href="InputIterator.html">input iterator</A>.  If your
compiler does not yet support member templates, though, then the
arguments must be of type <tt>const value_type*</tt>.
<P><A name="2">[2]</A>
Memory will be reallocated automatically if more than <tt>capacity() -
size()</tt> elements are inserted into the vector.  Reallocation does
not change <tt>size()</tt>, nor does it change the values of any
elements of the vector.  It does, however, increase
<tt>capacity()</tt>, and it invalidates <A href="#5">[5]</A> any
iterators that point into the vector.
<P><A name="3">[3]</A>
When it is necessary to increase <tt>capacity()</tt>, <tt>vector</tt>
usually increases it by a factor of two.  It is crucial that the
amount of growth is proportional to the current <tt>capacity()</tt>,
rather than a fixed constant: in the former case inserting a series of
elements into a vector is a linear time operation, and in the latter
case it is quadratic.
<P><A name="4">[4]</A>
<tt>Reserve()</tt> causes a reallocation manually.  The main reason
for using <tt>reserve()</tt> is efficiency: if you know the capacity
to which your <tt>vector</tt> must eventually grow, then it is usually
more efficient to allocate that memory all at once rather than relying
on the automatic reallocation scheme.  The other reason for using
<tt>reserve()</tt> is so that you can control the invalidation of
iterators. <A href="#5">[5]</A>
<P><A name="5">[5]</A>
A vector's iterators are invalidated when its memory is reallocated.
Additionally, inserting or deleting an element in the middle of a
vector invalidates all iterators that point to elements following the
insertion or deletion point.  It follows that you can prevent a
vector's iterators from being invalidated if you use
<tt>reserve()</tt> to preallocate as much memory as the vector will
ever use, and if all insertions and deletions are at the vector's end.
<h3>See also</h3>
<A href="Deque.html">deque</A>, 
<A href="List.html">list</A>, 
<A href="Slist.html">slist</A>

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