Difference between revisions of "cpp/container/vector"
m (mention that member function pages are better for info about invalidation) |
m (std::vector contiguous since c++03) |
||
| Line 10: | Line 10: | ||
{{tt|std::vector}} is a sequence container that encapsulates dynamic size arrays. | {{tt|std::vector}} is a sequence container that encapsulates dynamic size arrays. | ||
| − | The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets on regular pointers to elements. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array. | + | {{rev begin}} |
| + | {{rev | since=c++03 | The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets on regular pointers to elements. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array.}} | ||
| + | {{rev end}} | ||
The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using {{lc|capacity()}} function. {{rev inl | since=c++11 | Extra memory can be returned to the system via a call to {{lc|shrink_to_fit()}}.}} | The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using {{lc|capacity()}} function. {{rev inl | since=c++11 | Extra memory can be returned to the system via a call to {{lc|shrink_to_fit()}}.}} | ||
Revision as of 12:22, 23 December 2014
| Defined in header <vector>
|
||
| template< class T, |
||
std::vector is a sequence container that encapsulates dynamic size arrays.
| The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets on regular pointers to elements. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array. | (since C++03) |
The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using capacity() function. Extra memory can be returned to the system via a call to shrink_to_fit().(since C++11)
Reallocations are usually costly operations in terms of performance. reserve() function can be used to eliminate reallocations if the number of elements is known beforehand.
The complexity (efficiency) of common operations on vectors is as follows:
- Random access - constant O(1)
- Insertion or removal of elements at the end - amortized constant O(1)
- Insertion or removal of elements - linear in distance to the end of the vector O(n)
std::vector meets the requirements of Template:concept, Template:concept, Template:concept and Template:concept.
Contents |
Template parameters
| T | - | The type of the elements.
| ||||||||||||||
| Allocator | - | An allocator that is used to acquire/release memory and to construct/destroy the elements in that memory. The type must meet the requirements of Allocator. The behavior is undefined(until C++20)The program is ill-formed(since C++20) if Allocator::value_type is not the same as T.
|
Specializations
The standard library provides a specialization of std::vector for the type bool, which is optimized for space efficiency.
| space-efficient dynamic bitset (class template specialization) |
Iterator invalidation
| This section is incomplete |
There are still a few inaccuracies in this section. Refer to individual member function pages for more detail.
| Operations | Invalidated |
|---|---|
| All read only operations, swap, std::swap | Never |
| reserve, shrink_to_fit, clear, operator= | Always |
| erase | Erased elements + all elements after them (including end()) |
| push_back, emplace_back | If the vector changed capacity, all of them. If not, only end(). |
| insert, emplace, resize | If the vector changed capacity, all of them. If not, only those after the insertion point. |
| pop_back | The element erased and end(). |
Member types
| Member type | Definition | ||||
value_type
|
T
| ||||
allocator_type
|
Allocator
| ||||
size_type
|
Unsigned integer type (usually std::size_t) | ||||
difference_type
|
Signed integer type (usually std::ptrdiff_t) | ||||
reference
|
value_type& | ||||
const_reference
|
const value_type& | ||||
pointer
|
| ||||
const_pointer
|
| ||||
iterator
|
| ||||
const_iterator
|
| ||||
reverse_iterator
|
std::reverse_iterator<iterator> | ||||
const_reverse_iterator
|
std::reverse_iterator<const_iterator> |
Member functions
constructs the vector (public member function) | |
destructs the vector (public member function) | |
| assigns values to the container (public member function) | |
| assigns values to the container (public member function) | |
| returns the associated allocator (public member function) | |
Element access | |
| access specified element with bounds checking (public member function) | |
| access specified element (public member function) | |
| access the first element (public member function) | |
| access the last element (public member function) | |
| direct access to the underlying contiguous storage (public member function) | |
Iterators | |
| (C++11) |
returns an iterator to the beginning (public member function) |
| (C++11) |
returns an iterator to the end (public member function) |
| (C++11) |
returns a reverse iterator to the beginning (public member function) |
| (C++11) |
returns a reverse iterator to the end (public member function) |
Capacity | |
| checks whether the container is empty (public member function) | |
| returns the number of elements (public member function) | |
| returns the maximum possible number of elements (public member function) | |
| reserves storage (public member function) | |
| returns the number of elements that can be held in currently allocated storage (public member function) | |
| (DR*) |
reduces memory usage by freeing unused memory (public member function) |
Modifiers | |
| clears the contents (public member function) | |
| inserts elements (public member function) | |
| (C++11) |
constructs element in-place (public member function) |
| erases elements (public member function) | |
| adds an element to the end (public member function) | |
| (C++11) |
constructs an element in-place at the end (public member function) |
| removes the last element (public member function) | |
| changes the number of elements stored (public member function) | |
| swaps the contents (public member function) | |
Non-member functions
| (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20) |
lexicographically compares the values of two vectors (function template) |
| specializes the std::swap algorithm (function template) |
