在STL中向量vector是使用数组的形式实现的，因此向量具有顺序表的所有特点，可以快速随机存取任意元素。向量是同一种数据类型的对象的集合，每个对象根据其位置有一个整数索引值与其对应，类似于数组。与定义数组不同，向量在实例化是不需要声明长度，标准库负责管理和储存元素相关的内存，不用担心长度不够。
vector容器中的元素是连续存放的，当容器中增加一个新元素的时候，如果原来的存储空间刚好被用完，那么系统需要重新申请一块更大的连续存储空间，把原来的元素复制到新的空间，并在最后添加新元素，最后再撤销久空间。若每次增加新元素都要重复以上步骤，则会降低性能。实际上vector容器每次在申请内存的时候，都会额外申请一块连续的存储区，用于存放将来新加入的元素，从而不必每次都为新元素重新分配一次容器。当所有空间都被占满时，再重新申请一块新的空间。所分配的额外内存容量因库的不同而不同，这种分配策略使得vector容器具有显著的增长效率，提高了性能。
（1） 容器定义的类型别名
public:
typedef _Tp value_type;
typedef typename _Tp_alloc_type::pointer pointer;
typedef typename _Tp_alloc_type::const_pointer const_pointer;
typedef typename _Tp_alloc_type::reference reference;
typedef typename _Tp_alloc_type::const_reference const_reference;
typedef __gnu_cxx::__normal_iterator<pointer, vector_type> iterator;
typedef __gnu_cxx::__normal_iterator<const_pointer, vector_type>
const_iterator;
typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
typedef std::reverse_iterator<iterator> reverse_iterator;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef _Alloc allocator_type;
value_type： 元素类型
reference： 元素的左值类型，等效与value_type&
const_reference： 元素的常量左值类型
iterator： vector类型的迭代器类型
const_iterator： 元素的只读迭代器类型
const_reverse_iterator： 元素的只读逆序迭代器
reverse_iterator： 按逆序寻址元素的迭代器
size_type： 无符号整形
difference_type： 足够存储两个迭代器差值的有符号整形
（2） begin 和 end 成员
/**
* Returns a read/write iterator that points to the first
* element in the %vector. Iteration is done in ordinary
* element order.
*/
iterator
begin()
{ return iterator (this->_M_impl._M_start); }
/**
* Returns a read-only (constant) iterator that points to the
* first element in the %vector. Iteration is done in ordinary
* element order.
*/
const_iterator
begin() const
{ return const_iterator (this->_M_impl._M_start); }
/**
* Returns a read/write iterator that points one past the last
* element in the %vector. Iteration is done in ordinary
* element order.
*/
iterator
end()
{ return iterator (this->_M_impl._M_finish); }
/**
* Returns a read-only (constant) iterator that points one past
* the last element in the %vector. Iteration is done in
* ordinary element order.
*/
const_iterator
end() const
{ return const_iterator (this->_M_impl._M_finish); }
/**
* Returns a read/write reverse iterator that points to the
* last element in the %vector. Iteration is done in reverse
* element order.
*/
reverse_iterator
rbegin()
{ return reverse_iterator(end()); }
/**
* Returns a read-only (constant) reverse iterator that points
* to the last element in the %vector. Iteration is done in
* reverse element order.
*/
const_reverse_iterator
rbegin() const
{ return const_reverse_iterator(end()); }
/**
* Returns a read/write reverse iterator that points to one
* before the first element in the %vector. Iteration is done
* in reverse element order.
*/
reverse_iterator
rend()
{ return reverse_iterator(begin()); }
/**
* Returns a read-only (constant) reverse iterator that points
* to one before the first element in the %vector. Iteration
* is done in reverse element order.
*/
const_reverse_iterator
rend() const
{ return const_reverse_iterator(begin()); }
（3） 增删元素
/**
* @brief Add data to the end of the %vector.
* @param x Data to be added.
*
* This is a typical stack operation. The function creates an
* element at the end of the %vector and assigns the given data
* to it. Due to the nature of a %vector this operation can be
* done in constant time if the %vector has preallocated space
* available.
*/
void
push_back(const value_type& __x)
{
if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
{
this->_M_impl.construct(this->_M_impl._M_finish, __x);
++this->_M_impl._M_finish;
}
else
_M_insert_aux(end(), __x);
}
/**
* @brief Removes last element.
*
* This is a typical stack operation. It shrinks the %vector by one.
*
* Note that no data is returned, and if the last element's
* data is needed, it should be retrieved before pop_back() is
* called.
*/
void
pop_back()
{
--this->_M_impl._M_finish;
this->_M_impl.destroy(this->_M_impl._M_finish);
}
/**
* @brief Inserts given value into %vector before specified iterator.
* @param position An iterator into the %vector.
* @param x Data to be inserted.
* @return An iterator that points to the inserted data.
*
* This function will insert a copy of the given value before
* the specified location. Note that this kind of operation
* could be expensive for a %vector and if it is frequently
* used the user should consider using std::list.
*/
iterator
insert(iterator __position, const value_type& __x);
/**
* @brief Inserts a number of copies of given data into the %vector.
* @param position An iterator into the %vector.
* @param n Number of elements to be inserted.
* @param x Data to be inserted.
*
* This function will insert a specified number of copies of
* the given data before the location specified by @a position.
*
* Note that this kind of operation could be expensive for a
* %vector and if it is frequently used the user should
* consider using std::list.
*/
void
insert(iterator __position, size_type __n, const value_type& __x)
{ _M_fill_insert(__position, __n, __x); }
/**
* @brief Inserts a range into the %vector.
* @param position An iterator into the %vector.
* @param first An input iterator.
* @param last An input iterator.
*
* This function will insert copies of the data in the range
* [first,last) into the %vector before the location specified
* by @a pos.
*
* Note that this kind of operation could be expensive for a
* %vector and if it is frequently used the user should
* consider using std::list.
*/
template<typename _InputIterator>
void
insert(iterator __position, _InputIterator __first,
_InputIterator __last)
{
// Check whether it's an integral type. If so, it's not an iterator.
typedef typename std::__is_integer<_InputIterator>::__type _Integral;
_M_insert_dispatch(__position, __first, __last, _Integral());
}
/**
* @brief Remove element at given position.
* @param position Iterator pointing to element to be erased.
* @return An iterator pointing to the next element (or end()).
*
* This function will erase the element at the given position and thus
* shorten the %vector by one.
*
* Note This operation could be expensive and if it is
* frequently used the user should consider using std::list.
* The user is also cautioned that this function only erases
* the element, and that if the element is itself a pointer,
* the pointed-to memory is not touched in any way. Managing
* the pointer is the user's responsibilty.
*/
iterator
erase(iterator __position);
/**
* @brief Remove a range of elements.
* @param first Iterator pointing to the first element to be erased.
* @param last Iterator pointing to one past the last element to be
* erased.
* @return An iterator pointing to the element pointed to by @a last
* prior to erasing (or end()).
*
* This function will erase the elements in the range [first,last) and
* shorten the %vector accordingly.
*
* Note This operation could be expensive and if it is
* frequently used the user should consider using std::list.
* The user is also cautioned that this function only erases
* the elements, and that if the elements themselves are
* pointers, the pointed-to memory is not touched in any way.
* Managing the pointer is the user's responsibilty.
*/
iterator
erase(iterator __first, iterator __last);
/**
* Erases all the elements. Note that this function only erases the
* elements, and that if the elements themselves are pointers, the
* pointed-to memory is not touched in any way. Managing the pointer is
* the user's responsibilty.
*/
void
clear()
{
std::_Destroy(this->_M_impl._M_start, this->_M_impl._M_finish,
_M_get_Tp_allocator());
this->_M_impl._M_finish = this->_M_impl._M_start;
}
（4） 赋值与交换
/**
* @brief %Vector assignment operator.
* @param x A %vector of identical element and allocator types.
*
* All the elements of @a x are copied, but any extra memory in
* @a x (for fast expansion) will not be copied. Unlike the
* copy constructor, the allocator object is not copied.
*/
vector&
operator=(const vector& __x);
/**
* @brief Assigns a given value to a %vector.
* @param n Number of elements to be assigned.
* @param val Value to be assigned.
*
* This function fills a %vector with @a n copies of the given
* value. Note that the assignment completely changes the
* %vector and that the resulting %vector's size is the same as
* the number of elements assigned. Old data may be lost.
*/
void
assign(size_type __n, const value_type& __val)
{ _M_fill_assign(__n, __val); }
/**
* @brief Assigns a range to a %vector.
* @param first An input iterator.
* @param last An input iterator.
*
* This function fills a %vector with copies of the elements in the
* range [first,last).
*
* Note that the assignment completely changes the %vector and
* that the resulting %vector's size is the same as the number
* of elements assigned. Old data may be lost.
*/
template<typename _InputIterator>
void
assign(_InputIterator __first, _InputIterator __last)
{
// Check whether it's an integral type. If so, it's not an iterator.
typedef typename std::__is_integer<_InputIterator>::__type _Integral;
_M_assign_dispatch(__first, __last, _Integral());
}
/**
* @brief Swaps data with another %vector.
* @param x A %vector of the same element and allocator types.
*
* This exchanges the elements between two vectors in constant time.
* (Three pointers, so it should be quite fast.)
* Note that the global std::swap() function is specialized such that
* std::swap(v1,v2) will feed to this function.
*/
void
swap(vector& __x)
{
std::swap(this->_M_impl._M_start, __x._M_impl._M_start);
std::swap(this->_M_impl._M_finish, __x._M_impl._M_finish);
std::swap(this->_M_impl._M_end_of_storage,
__x._M_impl._M_end_of_storage);
}
（5） 容器大小的操作
/** Returns the number of elements in the %vector. */
size_type
size() const
{ return size_type(end() - begin()); }
/** Returns the size() of the largest possible %vector. */
size_type
max_size() const
{ return size_type(-1) / sizeof(value_type); }
/**
* @brief Resizes the %vector to the specified number of elements.
* @param new_size Number of elements the %vector should contain.
* @param x Data with which new elements should be populated.
*
* This function will %resize the %vector to the specified
* number of elements. If the number is smaller than the
* %vector's current size the %vector is truncated, otherwise
* the %vector is extended and new elements are populated with
* given data.
*/
void
resize(size_type __new_size, value_type __x = value_type())
{
if (__new_size < size())
erase(begin() + __new_size, end());
else
insert(end(), __new_size - size(), __x);
}
/**
* Returns the total number of elements that the %vector can
* hold before needing to allocate more memory.
*/
size_type
capacity() const
{ return size_type(const_iterator(this->_M_impl._M_end_of_storage)
- begin()); }
/**
* Returns true if the %vector is empty. (Thus begin() would
* equal end().)
*/
bool
empty() const
{ return begin() == end();
/**
* @brief Attempt to preallocate enough memory for specified number of
* elements.
* @param n Number of elements required.
* @throw std::length_error If @a n exceeds @c max_size().
*
* This function attempts to reserve enough memory for the
* %vector to hold the specified number of elements. If the
* number requested is more than max_size(), length_error is
* thrown.
*
* The advantage of this function is that if optimal code is a
* necessity and the user can determine the number of elements
* that will be required, the user can reserve the memory in
* %advance, and thus prevent a possible reallocation of memory
* and copying of %vector data.
*/
void
reserve(size_type __n);
（6） 访问元素
/**
* @brief Subscript access to the data contained in the %vector.
* @param n The index of the element for which data should be
* accessed.
* @return Read/write reference to data.
*
* This operator allows for easy, array-style, data access.
* Note that data access with this operator is unchecked and
* out_of_range lookups are not defined. (For checked lookups
* see at().)
*/
reference
operator[](size_type __n)
{ return *(begin() + __n); }
/**
* @brief Subscript access to the data contained in the %vector.
* @param n The index of the element for which data should be
* accessed.
* @return Read-only (constant) reference to data.
*
* This operator allows for easy, array-style, data access.
* Note that data access with this operator is unchecked and
* out_of_range lookups are not defined. (For checked lookups
* see at().)
*/
const_reference
operator[](size_type __n) const
{ return *(begin() + __n); }
/**
* @brief Provides access to the data contained in the %vector.
* @param n The index of the element for which data should be
* accessed.
* @return Read/write reference to data.
* @throw std::out_of_range If @a n is an invalid index.
*
* This function provides for safer data access. The parameter
* is first checked that it is in the range of the vector. The
* function throws out_of_range if the check fails.
*/
reference
at(size_type __n)
{
_M_range_check(__n);
return (*this)[__n];
}
/**
* @brief Provides access to the data contained in the %vector.
* @param n The index of the element for which data should be
* accessed.
* @return Read-only (constant) reference to data.
* @throw std::out_of_range If @a n is an invalid index.
*
* This function provides for safer data access. The parameter
* is first checked that it is in the range of the vector. The
* function throws out_of_range if the check fails.
*/
const_reference
at(size_type __n) const
{
_M_range_check(__n);
return (*this)[__n];
}
/**
* Returns a read/write reference to the data at the first
* element of the %vector.
*/
reference
front()
{ return *begin(); }
/**
* Returns a read-only (constant) reference to the data at the first
* element of the %vector.
*/
const_reference
front() const
{ return *begin(); }
/**
* Returns a read/write reference to the data at the last
* element of the %vector.
*/
reference
back()
{ return *(end() - 1); }
/**
* Returns a read-only (constant) reference to the data at the
* last element of the %vector.
*/
const_reference
back() const
{ return *(end() - 1); }
（7） 关系操作符
/**
* @brief Vector equality comparison.
* @param x A %vector.
* @param y A %vector of the same type as @a x.
* @return True iff the size and elements of the vectors are equal.
*
* This is an equivalence relation. It is linear in the size of the
* vectors. Vectors are considered equivalent if their sizes are equal,
* and if corresponding elements compare equal.
*/
template<typename _Tp, typename _Alloc>
inline bool
operator==(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{ return (__x.size() == __y.size()
&& std::equal(__x.begin(), __x.end(), __y.begin())); }
/**
* @brief Vector ordering relation.
* @param x A %vector.
* @param y A %vector of the same type as @a x.
* @return True iff @a x is lexicographically less than @a y.
*
* This is a total ordering relation. It is linear in the size of the
* vectors. The elements must be comparable with @c <.
*
* See std::lexicographical_compare() for how the determination is made.
*/
template<typename _Tp, typename _Alloc>
inline bool
operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{ return std::lexicographical_compare(__x.begin(), __x.end(),
__y.begin(), __y.end()); }
/// Based on operator==
template<typename _Tp, typename _Alloc>
inline bool
operator!=(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{ return !(__x == __y); }
/// Based on operator<
template<typename _Tp, typename _Alloc>
inline bool
operator>(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{ return __y < __x; }
/// Based on operator<
template<typename _Tp, typename _Alloc>
inline bool
operator<=(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{ return !(__y < __x); }
/// Based on operator<
template<typename _Tp, typename _Alloc>
inline bool
operator>=(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{ return !(__x < __y); }
（8） 构造函数
/**
* @brief Default constructor creates no elements.
*/
explicit
vector(const allocator_type& __a = allocator_type())
: _Base(__a)
{ }
/**
* @brief Create a %vector with copies of an exemplar element.
* @param n The number of elements to initially create.
* @param value An element to copy.
*
* This constructor fills the %vector with @a n copies of @a value.
*/
explicit
vector(size_type __n, const value_type& __value = value_type(),
const allocator_type& __a = allocator_type())
: _Base(__n, __a)
{
std::__uninitialized_fill_n_a(this->_M_impl._M_start, __n, __value,
_M_get_Tp_allocator());
this->_M_impl._M_finish = this->_M_impl._M_start + __n;
}
/**
* @brief %Vector copy constructor.
* @param x A %vector of identical element and allocator types.
*
* The newly-created %vector uses a copy of the allocation
* object used by @a x. All the elements of @a x are copied,
* but any extra memory in
* @a x (for fast expansion) will not be copied.
*/
vector(const vector& __x)
: _Base(__x.size(), __x.get_allocator())
{ this->_M_impl._M_finish =
std::__uninitialized_copy_a(__x.begin(), __x.end(),
this->_M_impl._M_start,
_M_get_Tp_allocator());
}
/**
* @brief Builds a %vector from a range.
* @param first An input iterator.
* @param last An input iterator.
*
* Create a %vector consisting of copies of the elements from
* [first,last).
*
* If the iterators are forward, bidirectional, or
* random-access, then this will call the elements' copy
* constructor N times (where N is distance(first,last)) and do
* no memory reallocation. But if only input iterators are
* used, then this will do at most 2N calls to the copy
* constructor, and logN memory reallocations.
*/
template<typename _InputIterator>
vector(_InputIterator __first, _InputIterator __last,
const allocator_type& __a = allocator_type())
: _Base(__a)
{
// Check whether it's an integral type. If so, it's not an iterator.
typedef typename std::__is_integer<_InputIterator>::__type _Integral;
_M_initialize_dispatch(__first, __last, _Integral());
}
定义vector对象时必须说明其保存的对象类型。以下是定义向量对象的一些例子：
vector ＜int＞ ivec； //定义向量对象ivec vector ＜int＞ ivec1（ivec）； //定义向量对象ivec2，并用ivec初始化 vector ＜int＞ ivec2（ｎ，ｉ）； //定义向量对象ivec2，包含了ｎ个值为ｉ的元素 vector ＜int＞ ivec3（ｎ）； //定义向量对象ivec3，包含了ｎ个值为０的元素 vector＜vector ＜int＞ ＞ vivec； //定义向量对象vivec，这是一个容器的容器。注意两个“＞”之间要有空格
版权声明：本文为博主原创文章，未经博主允许不得转载。
原文：http://blog.csdn.net/liuruiqun/article/details/46818367