vector

Container

• Summary
• Data Type and Member Function Indexes
• Synopsis
• Description
• Special Case
• Interface
• Constructors
• Destructor
• Iterators
• Assignment Operator
• Allocator
• Reference Operators
• Member Functions
• Non-member Operators
• Specialized Algorithms
• Example
• Warnings
• See Also

A sequence that supports random access iterators.

Member Functions
assign() at() back() begin() capacity() clear() empty() end() erase() flip()	front() get_allocator() insert() max_size() operator!=() operator>() operator>=() operator<() operator<=() operator=()	operator==() operator[]() pop_back() push_back() rbegin() rend() reserve() resize() size() swap()

#include <vector>
template <class T, class Allocator = allocator<T> >
class vector ;

vector<T, Allocator> is a type of sequence that supports random access iterators. In addition, it supports amortized constant time insert and erase operations at the end. Insert and erase in the middle take linear time. Storage management is handled automatically. In vector, iterator is a random access iterator referring to T. const_iterator is a constant random access iterator that returns a const T& when dereferenced. A constructor for iterator and const_iterator is guaranteed. size_type is an unsigned integral type. difference_type is a signed integral type.

Any type used for the template parameter T must provide the following (where T is the type, t is a value of T and u is a const value of T):

  Copy constructors     T(t) and T(u)
  Destructor            t.~T()
  Address of            &t and &u yielding T* and const T*
                        respectively
  Assignment            t = a where a is a
                        (possibly const) value of T

Vectors of bit values, that is boolean 1/0 values, are handled as a special case by the standard library, so that they can be efficiently packed several elements to a word. The operations for a boolean vector, vector<bool>, are a superset of those for an ordinary vector, only the implementation is more efficient.

Two member functions are available to the boolean vector data type. One is flip(), which inverts all the bits of the vector. Boolean vectors also return as reference an internal value that also supports the flip() member function. The other vector<bool>-specific member function is a second form of the swap() function

template <class T, class Allocator = allocator<T> >
class vector {
public:
// Types
typedef T value_type;
typedef Allocator allocator_type;
typedef typename Allocator::reference reference;
typedef typename Allocator::const_reference const_reference; 
class iterator;
class const_iterator;
typedef typename Allocator::size_type size_type;
typedef typename Allocator::difference_type difference_type;
typedef typename std::reverse_iterator<iterator>
                 reverse_iterator;
typedef typename std::reverse_iterator<const iterator>
                 const_reverse_iterator;

// Construct/Copy/Destroy
explicit vector (const Allocator& = Allocator());
explicit vector (size_type, const Allocator& = Allocator ());
vector (size_type, const T&, const Allocator& = Allocator());
vector (const vector<T, Allocator>&);
template <class InputIterator>
vector (InputIterator, InputIterator, 
const Allocator& = Allocator ());
~vector ();
vector<T,Allocator>& operator= (const vector<T, Allocator>&);
template <class InputIterator>
void assign (InputIterator first, InputIterator last);
void assign (size_type, const);
allocator_type get_allocator () const;
// Iterators
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;

// Capacity
size_type size () const;
size_type max_size () const;
void resize (size_type);
void resize (size_type, T);
size_type capacity () const;
bool empty () const;
void reserve (size_type);

// Element Access
reference operator[] (size_type);
const_reference operator[] (size_type) const;
reference at (size_type);
const_reference at (size_type) const;
reference front ();
const_reference front () const;
reference back ();
const_reference back () const;

// Modifiers
void push_back (const T&);
void pop_back ();
iterator insert (iterator, const T&);
void insert (iterator, size_type, const T&);
template <class InputIterator>
void insert (iterator, InputIterator, InputIterator);
iterator erase (iterator);
iterator erase (iterator, iterator);
void swap (vector<T, Allocator>&);
void clear()
};

// Non-member Operators
template <class T>
bool operator== (const vector<T,Allocator>&, 
const vector <T,Allocator>&);
template <class T>
bool operator!= (const vector<T,Allocator>&, 
const vector <T,Allocator>&);
template <class T>
bool operator< (const vector<T,Allocator>&, 
const vector<T,Allocator>&);
template <class T>
bool operator> (const vector<T,Allocator>&, 
const vector<T,Allocator>&);
template <class T>
bool operator<= (const vector<T,Allocator>&, 
const vector<T,Allocator>&);
template <class T>
bool operator>= (const vector<T,Allocator>&, 
const vector<T,Allocator>&);

// Specialized Algorithms
template <class T, class Allocator>
void swap (const vector<T,Allocator>&, const vector<T,Allocator>&);

explicit vector(const Allocator& alloc = Allocator());

The default constructor. Creates a vector of length zero. The vector will use the allocator alloc for all storage management.

explicit vector(size_type n);

Creates a vector of length n, containing n copies of the default value for type T. Requires that T have a default constructor. The vector will use the allocator Allocator() for all storage management.

vector(size_type n, const T& value,
const Allocator& alloc = Allocator());

Creates a vector of length n, containing n copies of value. The vector will use the allocator alloc for all storage management.

vector(const vector<T, Allocator>& x);

Creates a copy of x.

template <class InputIterator>
vector(InputIterator first, InputIterator last,
const Allocator& alloc = Allocator());

Creates a vector of length last - first, filled with all values obtained by dereferencing the InputIterators on the range [first, last). The vector will use the allocator alloc for all storage management.

~vector();

The destructor. Releases any allocated memory for this vector.

iterator 
begin();

Returns a random access iterator that points to the first element.

const_iterator 
begin() const;

Returns a random access const_iterator that points to the first element.

iterator 
end();

Returns a random access iterator that points to the past-the-end value.

const_iterator 
end() const;

Returns a random access const_iterator that points to the past-the-end value.

reverse_iterator 
rbegin();

Returns a random access reverse_iterator that points to the past-the-end value.

const_reverse_iterator 
rbegin() const;

Returns a random access const_reverse_iterator that points to the past-the-end value.

reverse_iterator 
rend();

Returns a random access reverse_iterator that points to the first element.

const_reverse_iterator 
rend() const;

Returns a random access const_reverse_iterator that points to the first element.

vector<T, Allocator>& 
operator=(const vector<T, Allocator>& x);

Erases all elements in self then inserts into self a copy of each element in x. Returns a reference to self.

allocator_type 
get_allocator() const;

Returns a copy of the allocator used by self for storage management.

reference 
operator[](size_type n);

Returns a reference to element n of self. The result can be used as an lvalue. The index n must be between 0 and the size less one.

const_reference 
operator[](size_type n) const;

Returns a constant reference to element n of self. The index n must be between 0 and the size less one.

template <class InputIterator>
void 
assign(InputIterator first, InputIterator last);

Erases all elements contained in self, then inserts new elements from the range [first, last).

void 
assign(size_type, const T& t); 

Erases all elements contained in self, then inserts n instances of the value of t.

reference 
at(size_type n);

Returns a reference to element n of self. The result can be used as an lvalue. The index n must be between 0 and the size less one.

const_reference 
at(size_type) const;

Returns a constant reference to element n of self. The index n must be between 0 and the size less one.

reference 
back();

Returns a reference to the last element.

const_reference 
back() const;

Returns a constant reference to the last element.

size_type 
capacity() const;

Returns the size of the allocated storage, as the number of elements that can be stored.

void 
clear() ; 

Deletes all elements from the vector.

bool 
empty() const;

Returns true if the size is zero.

iterator
erase(iterator position);

Deletes the vector element pointed to by the iterator position. Returns an iterator pointing to the element following the deleted element, or end() if the deleted element was the last one in this vector.

iterator
erase(iterator first, iterator last);

Deletes the vector elements in the range (first, last). Returns an iterator pointing to the element following the last deleted element, or end() if there were no elements in the deleted range.

void
flip();

Flips all the bits in the vector. This member function is only defined for vector<bool>.

reference 
front();

Returns a reference to the first element.

const_reference 
front() const;

Returns a constant reference to the first element.

iterator 
insert(iterator position, const T& x);

Inserts x before position. The return value points to the inserted x.

void 
insert(iterator position, size_type n, const  T& x);

Inserts n copies of x before position.

template <class InputIterator>
void 
insert(iterator position, InputIterator first, 
InputIterator last);

Inserts copies of the elements in the range [first, last] before position.

size_type 
max_size() const;

Returns size() of the largest possible vector.

void 
pop_back();

Removes the last element of self.

void 
push_back(const T& x);

Inserts a copy of x to the end of self.

void 
reserve(size_type n);

Increases the capacity of self in anticipation of adding new elements. reserve itself does not add any new elements. After a call to reserve, capacity() is greater than or equal to n and subsequent insertions will not cause a reallocation until the size of the vector exceeds n. Reallocation does not occur if n is less than capacity(). If reallocation does occur, then all iterators and references pointing to elements in the vector are invalidated. reserve takes at most linear time in the size of self. reserve throws a length_error exception if n is greater than max_size().

void 
resize(size_type sz);

Alters the size of self. If the new size (sz) is greater than the current size, then sz-size() instances of the default value of type T are inserted at the end of the vector. If the new size is smaller than the current capacity, then the vector is truncated by erasing size()-sz elements off the end. If sz is equal to capacity then no action is taken.

void 
resize(size_type sz, T c);

Alters the size of self. If the new size (sz) is greater than the current size, then sz-size() c's are inserted at the end of the vector. If the new size is smaller than the current capacity, then the vector is truncated by erasing size()-sz elements off the end. If sz is equal to capacity then no action is taken.

size_type 
size() const;

Returns the number of elements.

void 
swap(vector<T, Allocator>& x);

Exchanges self with x, by swapping all elements.

void
swap(reference x, reference y);

Swaps the values of x and y. This is a member function of vector<bool> only.

template <class T, class Allocator>
bool operator==(const vector<T, Allocator>& x,
const vector<T, Allocator>& y);

Returns true if x is the same as y.

template <class T, class Allocator>
bool operator!=(const vector<T, Allocator>& x,
const vector<T, Allocator>& y);

Returns !(x==y).

template <class T>
bool operator<(const vector<T, Allocator>& x,
const vector<T, Allocator>& y);

Returns true if the elements contained in x are lexicographically less than the elements contained in y.

template <class T>
bool operator>(const vector<T, Allocator>& x,
const vector<T, Allocator>& y);

Returns y < x.

template <class T>
bool operator<=(const vector<T, Allocator>& x,
const vector<T, Allocator>& y);

Returns !(y < x).

template <class T>
bool operator>=(const vector<T, Allocator>& x,
const vector<T, Allocator>& y);

Returns !(x < y).

template <class T, class Allocator>void 
swap(vector <T, Allocator>& a, vector <T, Allocator>& b);

Efficiently swaps the contents of a and b.

//
// vector.cpp
//
#include <vector>
#include <iostream>

ostream& operator<< (ostream& out, 
const vector<int, allocator>& v)
 {
  copy(v.begin(),v.end(),ostream_iterator<int,char>(out," "));
  return out;
 }
int main(void)
 {
// create a vector of doubles
   vector<int>         vi;
   int                 i;

for(i = 0; i < 10; ++i) {
   // insert values before the beginning
   vi.insert(vi.begin(), i);
   }

// print out the vector
cout << vi << endl;

// now let's erase half of the elements
int half = vi.size() >> 1;
for(i = 0; i < half; ++i) {
   vi.erase(vi.begin());
   }

// print ir out again
cout << vi << endl;

return 0;
 }

Output : 
9 8 7 6 5 4 3 2 1 0
4 3 2 1 0

Member function templates are used in all containers provided by the Standard Template Library. An example of this feature is the constructor for vector<T, Allocator> that takes two templated iterators:

template <class InputIterator>
vector (InputIterator, InputIterator,
const Allocator = Allocator());

vector also has an insert function of this type. These functions, when not restricted by compiler limitations, allow you to use any type of input iterator as arguments. For compilers that do not support this feature we provide substitute functions that allow you to use an iterator obtained from the same type of container as the one you are constructing (or calling a member function on), or you can use a pointer to the type of element you have in the container.

For example, if your compiler does not support member function templates you can construct a vector in the following two ways:

int intarray[10];
vector<int> first_vector(intarray, intarray + 10);
vector<int> second_vector(first_vector.begin(), 
first_vector.end());

but not this way:

vector<long>
long_vector(first_vector.begin(),first_vector.end());

since the long_vector and first_vector are not the same type.

Additionally, if your compiler does not support default template parameters, you will need to supply the Allocator template argument. For instance, you will need to write :

vector<int, allocator<int> >

instead of :

vector<int>

allocator, Containers, Iterators, lexicographical_compare