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Difference between revisions of "cpp/container/deque"

From cppreference.com
< cpp‎ | container
(those were not invalidation notes (so they were in the wrong section); also nearly all of that was already said on this page, in fewer words. Large min cost was missing though, adding that and extra runtime cost on indexed access up top)
m (→‎Deduction guides: ~)
 
(32 intermediate revisions by 15 users not shown)
Line 3: Line 3:
 
{{dcl begin}}
 
{{dcl begin}}
 
{{dcl header|deque}}
 
{{dcl header|deque}}
−
{{dcl | num=1 |
+
{{dcl|num=1|1=
 
template<
 
template<
 
     class T,
 
     class T,
−
     class Allocator {{=}} std::allocator<T>
+
     class Allocator = std::allocator<T>
 
> class deque;
 
> class deque;
−
}}  
+
}}
−
{{dcl | num=2 |since=c++17|1=
+
{{dcl|num=2|since=c++17|1=
 
namespace pmr {
 
namespace pmr {
−
     template <class T>
+
     template< class T >
 
     using deque = std::deque<T, std::pmr::polymorphic_allocator<T>>;
 
     using deque = std::deque<T, std::pmr::polymorphic_allocator<T>>;
 
}
 
}
Line 19: Line 19:
 
{{tt|std::deque}} (double-ended queue) is an indexed sequence container that allows fast insertion and deletion at both its beginning and its end. In addition, insertion and deletion at either end of a deque never invalidates pointers or references to the rest of the elements.
 
{{tt|std::deque}} (double-ended queue) is an indexed sequence container that allows fast insertion and deletion at both its beginning and its end. In addition, insertion and deletion at either end of a deque never invalidates pointers or references to the rest of the elements.
  
−
As opposed to {{lc|std::vector}}, the elements of a deque are not stored contiguously: typical implementations use a sequence of individually allocated fixed-size arrays, with additional bookkeeping, which means indexed access to std:deque must perform two pointer dereferences, compared to vector's indexed access which performs only one.
+
As opposed to {{lc|std::vector}}, the elements of a deque are not stored contiguously: typical implementations use a sequence of individually allocated fixed-size arrays, with additional bookkeeping, which means indexed access to deque must perform two pointer dereferences, compared to vector's indexed access which performs only one.
  
−
The storage of a deque is automatically expanded and contracted as needed. Expansion of a deque is cheaper than the expansion of a {{lc|std::vector}} because it does not involve copying of the existing elements to a new memory location. On the other hand, deques typically have large minimal memory cost; a deque holding just one element has to allocate its full internal array (e.g. 656 bytes on 64-bit libstdc++).
+
The storage of a deque is automatically expanded and contracted as needed. Expansion of a deque is cheaper than the expansion of a {{lc|std::vector}} because it does not involve copying of the existing elements to a new memory location. On the other hand, deques typically have large minimal memory cost; a deque holding just one element has to allocate its full internal array (e.g. 8 times the object size on 64-bit libstdc++; 16 times the object size or 4096 bytes, whichever is larger, on 64-bit libc++).
  
 
The complexity (efficiency) of common operations on deques is as follows:
 
The complexity (efficiency) of common operations on deques is as follows:
  
−
* Random access - constant {{math|O(1)}}
+
* Random access - constant {{math|O(1)}}.
−
* Insertion or removal of elements at the end or beginning - constant {{math|O(1)}}
+
* Insertion or removal of elements at the end or beginning - constant {{math|O(1)}}.
−
* Insertion or removal of elements - linear {{math|O(n)}}
+
* Insertion or removal of elements - linear {{math|O(n)}}.
  
−
{{tt|std::deque}} meets the requirements of {{concept|Container}}, {{concept|AllocatorAwareContainer}}, {{concept|SequenceContainer}} and {{concept|ReversibleContainer}}.
+
{{tt|std::deque}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|SequenceContainer}} and {{named req|ReversibleContainer}}.
  
 
===Template parameters===
 
===Template parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par inc | cpp/container/param list T | deque}}
+
{{par inc|cpp/container/param list T|deque}}
−
{{par inc | cpp/container/param list Allocator | deque}}
+
{{par inc|cpp/container/param list Allocator|deque}}
 
{{par end}}
 
{{par end}}
  
 
===Iterator invalidation===
 
===Iterator invalidation===
−
{{todo}}
+
{{todo|There are still a few inaccuracies in this section, refer to individual member function pages for more detail}}
−
There are still a few inaccuracies in this section, refer to individual member function pages for more detail
+
  
−
{| class="dsctable" style="font-size:0.8em"
+
{|class="dsctable" style="font-size:0.9em"
−
! Operations
+
!Operations
−
! Invalidated
+
!Invalidated
 
|-
 
|-
−
| All read only operations
+
|All read only operations.
−
| Never
+
|Never.
 
|-
 
|-
−
| {{lc|swap}}, {{lc|std::swap}}
+
|{{lc|swap}}, {{lc|std::swap}}
−
| The past-the-end iterator may be invalidated (implementation defined)
+
|The past-the-end iterator may be invalidated (implementation defined).
 
|-
 
|-
−
| {{lc|shrink_to_fit}}, {{lc|clear}}, {{lc|insert}}, {{lc|emplace}}, {{lc|push_front}}, {{lc|push_back}}, {{lc|emplace_front}}, {{lc|emplace_back}}
+
|{{lc|shrink_to_fit}}, {{lc|clear}}, {{lc|insert}}, {{lc|emplace}}, {{lc|push_front}},<br>{{lc|push_back}}, {{lc|emplace_front}}, {{lc|emplace_back}}
−
| Always
+
|Always.
 
|-
 
|-
−
| {{lc|erase}}
+
|{{lc|erase}}
−
| If erasing at begin - only erased elements<br>
+
|If erasing at begin - only erased elements.<br>
−
If erasing at end - only erased elements and the past-the-end iterator<br>
+
If erasing at end - only erased elements and the past-the-end iterator.<br>
−
Otherwise - all iterators are invalidated (including the past-the-end iterator).
+
Otherwise - all iterators are invalidated.<br><br>
 +
{{rev inl|until=c++11|It is unspecified when the past-the-end iterator is invalidated.}}<br><br>
 +
{{rev inl|since=c++11|The past-the-end iterator is also invalidated unless the erased<br>
 +
elements are at the beginning of the container and the last element is not erased.}}
 
|-
 
|-
−
| {{lc|resize}}
+
|{{lc|resize}}
−
| If the new size is smaller than the old one : only erased elements and the past-the-end iterator<br>
+
|If the new size is smaller than the old one - only erased elements and the<br> past-the-end iterator.<br>
−
If the new size is bigger than the old one : all iterators are invalidated<br>
+
If the new size is bigger than the old one - all iterators are invalidated.<br>
 
Otherwise - none iterators are invalidated.
 
Otherwise - none iterators are invalidated.
 
|-
 
|-
−
| {{lc|pop_front}}
+
|{{lc|pop_front}}, {{lc|pop_back}}
−
| Only to the element erased
+
|To the element erased.<br>
−
|-
+
The past-the-end iterator<br>
−
| {{lc|pop_back}}
+
{{rev inl|until=c++11|may be invalidated (implementation defined)}}<br>
−
| Only to the element erased and the past-the-end iterator
+
{{rev inl|since=c++11|is also invalidated.}}
 
|}
 
|}
  
Line 80: Line 82:
 
===Member types===
 
===Member types===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc hitem | Member type | Definition}}
+
{{dsc hitem|Member type|Definition}}
−
{{dsc inc | cpp/container/dsc value_type | deque}}
+
{{dsc inc|cpp/container/dsc value_type|deque}}
−
{{dsc inc | cpp/container/dsc allocator_type | deque}}
+
{{dsc inc|cpp/container/dsc allocator_type|deque}}
−
{{dsc inc | cpp/container/dsc size_type | deque}}
+
{{dsc inc|cpp/container/dsc size_type|deque}}
−
{{dsc inc | cpp/container/dsc difference_type | deque}}
+
{{dsc inc|cpp/container/dsc difference_type|deque}}
−
{{dsc inc | cpp/container/dsc reference | deque}}
+
{{dsc inc|cpp/container/dsc reference|deque}}
−
{{dsc inc | cpp/container/dsc const_reference | deque}}
+
{{dsc inc|cpp/container/dsc const_reference|deque}}
−
{{dsc inc | cpp/container/dsc pointer | deque}}
+
{{dsc inc|cpp/container/dsc pointer|deque}}
−
{{dsc inc | cpp/container/dsc const_pointer | deque}}
+
{{dsc inc|cpp/container/dsc const_pointer|deque}}
−
{{dsc inc | cpp/container/dsc iterator | deque}}
+
{{dsc inc|cpp/container/dsc iterator|deque}}
−
{{dsc inc | cpp/container/dsc const_iterator | deque}}
+
{{dsc inc|cpp/container/dsc const_iterator|deque}}
−
{{dsc inc | cpp/container/dsc reverse_iterator | deque}}
+
{{dsc inc|cpp/container/dsc reverse_iterator|deque}}
−
{{dsc inc | cpp/container/dsc const_reverse_iterator | deque}}
+
{{dsc inc|cpp/container/dsc const_reverse_iterator|deque}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Member functions===
 
===Member functions===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc constructor | deque}}
+
{{dsc inc|cpp/container/dsc constructor|deque}}
−
{{dsc inc | cpp/container/dsc destructor | deque}}
+
{{dsc inc|cpp/container/dsc destructor|deque}}
−
{{dsc inc | cpp/container/dsc operator{{=}} | deque}}
+
{{dsc inc|cpp/container/dsc operator{{=}}|deque}}
−
{{dsc inc | cpp/container/dsc assign | deque}}
+
{{dsc inc|cpp/container/dsc assign|deque}}
−
{{dsc inc | cpp/container/dsc get_allocator | deque}}
+
{{dsc inc|cpp/container/dsc assign_range|deque}}
 +
{{dsc inc|cpp/container/dsc get_allocator|deque}}
  
−
{{dsc h2 | Element access}}
+
{{dsc h2|Element access}}
−
{{dsc inc | cpp/container/dsc at | deque}}
+
{{dsc inc|cpp/container/dsc at|deque}}
−
{{dsc inc | cpp/container/dsc operator_at | deque}}
+
{{dsc inc|cpp/container/dsc operator_at|deque}}
−
{{dsc inc | cpp/container/dsc front | deque}}
+
{{dsc inc|cpp/container/dsc front|deque}}
−
{{dsc inc | cpp/container/dsc back | deque}}
+
{{dsc inc|cpp/container/dsc back|deque}}
  
−
{{dsc h2 | Iterators}}
+
{{dsc h2|Iterators}}
−
{{dsc inc | cpp/container/dsc begin | deque}}
+
{{dsc inc|cpp/container/dsc begin|deque}}
−
{{dsc inc | cpp/container/dsc end | deque}}
+
{{dsc inc|cpp/container/dsc end|deque}}
−
{{dsc inc | cpp/container/dsc rbegin | deque}}
+
{{dsc inc|cpp/container/dsc rbegin|deque}}
−
{{dsc inc | cpp/container/dsc rend | deque}}
+
{{dsc inc|cpp/container/dsc rend|deque}}
  
−
{{dsc h2 | Capacity}}
+
{{dsc h2|Capacity}}
−
{{dsc inc | cpp/container/dsc empty | deque}}
+
{{dsc inc|cpp/container/dsc empty|deque}}
−
{{dsc inc | cpp/container/dsc size | deque}}
+
{{dsc inc|cpp/container/dsc size|deque}}
−
{{dsc inc | cpp/container/dsc max_size | deque}}
+
{{dsc inc|cpp/container/dsc max_size|deque}}
−
{{dsc inc | cpp/container/dsc shrink_to_fit | deque}}
+
{{dsc inc|cpp/container/dsc shrink_to_fit|deque}}
  
−
{{dsc h2 | Modifiers}}
+
{{dsc h2|Modifiers}}
−
{{dsc inc | cpp/container/dsc clear | deque}}
+
{{dsc inc|cpp/container/dsc clear|deque}}
−
{{dsc inc | cpp/container/dsc insert | deque}}
+
{{dsc inc|cpp/container/dsc insert|deque}}
−
{{dsc inc | cpp/container/dsc emplace | deque}}
+
{{dsc inc|cpp/container/dsc insert_range|deque}}
−
{{dsc inc | cpp/container/dsc erase | deque}}
+
{{dsc inc|cpp/container/dsc emplace|deque}}
−
{{dsc inc | cpp/container/dsc push_back | deque}}
+
{{dsc inc|cpp/container/dsc erase|deque}}
−
{{dsc inc | cpp/container/dsc emplace_back | deque}}
+
{{dsc inc|cpp/container/dsc push_back|deque}}
−
{{dsc inc | cpp/container/dsc pop_back | deque}}
+
{{dsc inc|cpp/container/dsc emplace_back|deque}}
−
{{dsc inc | cpp/container/dsc push_front | deque}}
+
{{dsc inc|cpp/container/dsc append_range|deque}}
−
{{dsc inc | cpp/container/dsc emplace_front | deque}}
+
{{dsc inc|cpp/container/dsc pop_back|deque}}
−
{{dsc inc | cpp/container/dsc pop_front | deque}}
+
{{dsc inc|cpp/container/dsc push_front|deque}}
−
{{dsc inc | cpp/container/dsc resize | deque}}
+
{{dsc inc|cpp/container/dsc emplace_front|deque}}
−
{{dsc inc | cpp/container/dsc swap | deque}}
+
{{dsc inc|cpp/container/dsc prepend_range|deque}}
 +
{{dsc inc|cpp/container/dsc pop_front|deque}}
 +
{{dsc inc|cpp/container/dsc resize|deque}}
 +
{{dsc inc|cpp/container/dsc swap|deque}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Non-member functions===
 
===Non-member functions===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc operator_cmp | deque}}
+
{{dsc inc|cpp/container/dsc operator_cmp|deque}}
−
{{dsc inc | cpp/container/dsc swap2 | deque}}
+
{{dsc inc|cpp/container/dsc swap2|deque}}
 +
{{dsc inc|cpp/container/dsc erase seq|deque}}
 
{{dsc end}}
 
{{dsc end}}
  
−
===Example===
+
{{rrev|since=c++17|
 +
==={{rl|deduction guides|Deduction guides}}===
 +
}}
  
 +
===Notes===
 +
{{ftm begin|std=1|comment=1}}
 +
{{ftm|__cpp_lib_containers_ranges|value=202202L|std=C++23|Ranges construction and insertion for containers}}
 +
{{ftm end}}
 +
 +
===Example===
 
{{example
 
{{example
−
|
+
|code=
−
| code=
+
−
#include <iostream>
+
 
#include <deque>
 
#include <deque>
 +
#include <iostream>
  
 
int main()
 
int main()
Line 154: Line 168:
 
     // Create a deque containing integers
 
     // Create a deque containing integers
 
     std::deque<int> d = {7, 5, 16, 8};
 
     std::deque<int> d = {7, 5, 16, 8};
−
 
+
   
 
     // Add an integer to the beginning and end of the deque
 
     // Add an integer to the beginning and end of the deque
 
     d.push_front(13);
 
     d.push_front(13);
 
     d.push_back(25);
 
     d.push_back(25);
−
 
+
   
 
     // Iterate and print values of deque
 
     // Iterate and print values of deque
−
     for(int n : d) {
+
     for (int n : d)
−
         std::cout << n << '\n';
+
         std::cout << n << ' ';
−
     }
+
     std::cout << '\n';
 
}
 
}
−
| output=
+
|output=
−
13
+
13 7 5 16 8 25
−
7
+
−
5
+
−
16
+
−
8
+
−
25
+
 
}}
 
}}
  
−
[[de:cpp/container/deque]]
+
===Defect reports===
−
[[es:cpp/container/deque]]
+
{{dr list begin}}
−
[[fr:cpp/container/deque]]
+
{{dr list item|wg=lwg|dr=230|std=C++98|before={{tt|T}} was not required to be {{named req|CopyConstructible}}<br>(an element of type {{tt|T}} might not be able to be constructed)|after={{tt|T}} is also required to<br>be {{named req|CopyConstructible}}}}
−
[[it:cpp/container/deque]]
+
{{dr list end}}
−
[[ja:cpp/container/deque]]
+
 
−
[[pt:cpp/container/deque]]
+
===See also===
−
[[ru:cpp/container/deque]]
+
{{dsc begin}}
−
[[zh:cpp/container/deque]]
+
{{dsc inc|cpp/container/dsc queue}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pl|pt|ru|zh}}

Latest revision as of 22:51, 13 November 2023

 
C++
 
Containers library
 
std::deque
Member types
Member functions
Non-member functions
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides(C++17)
 
Defined in header <deque>
template<

    class T,
    class Allocator = std::allocator<T>

> class deque;
 (1)
namespace pmr {

    template< class T >
    using deque = std::deque<T, std::pmr::polymorphic_allocator<T>>;

}
 (2) (since C++17)

std::deque (double-ended queue) is an indexed sequence container that allows fast insertion and deletion at both its beginning and its end. In addition, insertion and deletion at either end of a deque never invalidates pointers or references to the rest of the elements.

As opposed to std::vector, the elements of a deque are not stored contiguously: typical implementations use a sequence of individually allocated fixed-size arrays, with additional bookkeeping, which means indexed access to deque must perform two pointer dereferences, compared to vector's indexed access which performs only one.

The storage of a deque is automatically expanded and contracted as needed. Expansion of a deque is cheaper than the expansion of a std::vector because it does not involve copying of the existing elements to a new memory location. On the other hand, deques typically have large minimal memory cost; a deque holding just one element has to allocate its full internal array (e.g. 8 times the object size on 64-bit libstdc++; 16 times the object size or 4096 bytes, whichever is larger, on 64-bit libc++).

The complexity (efficiency) of common operations on deques is as follows:

  • Random access - constant O(1).
  • Insertion or removal of elements at the end or beginning - constant O(1).
  • Insertion or removal of elements - linear O(n).

std::deque meets the requirements of Container, AllocatorAwareContainer, SequenceContainer and ReversibleContainer.

Contents

[edit] Template parameters

T - The type of the elements.
T must meet the requirements of CopyAssignable and CopyConstructible. (until C++11)
The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type is a complete type and meets the requirements of Erasable, but many member functions impose stricter requirements. (since C++11)

[edit]

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.[edit]

[edit] Iterator invalidation

This section is incomplete
Reason: There are still a few inaccuracies in this section, refer to individual member function pages for more detail
Operations Invalidated
All read only operations. Never.
swap, std::swap The past-the-end iterator may be invalidated (implementation defined).
shrink_to_fit, clear, insert, emplace, push_front,
push_back, emplace_front, emplace_back 		Always.
erase If erasing at begin - only erased elements.

If erasing at end - only erased elements and the past-the-end iterator.
Otherwise - all iterators are invalidated.

It is unspecified when the past-the-end iterator is invalidated.(until C++11)

The past-the-end iterator is also invalidated unless the erased
elements are at the beginning of the container and the last element is not erased.(since C++11)

resize If the new size is smaller than the old one - only erased elements and the
past-the-end iterator.

If the new size is bigger than the old one - all iterators are invalidated.
Otherwise - none iterators are invalidated.

pop_front, pop_back To the element erased.

The past-the-end iterator
may be invalidated (implementation defined)(until C++11)
is also invalidated.(since C++11)

[edit] Invalidation notes

  • When inserting at either end of the deque, references are not invalidated by insert and emplace.
  • push_front, push_back, emplace_front and emplace_back do not invalidate any references to elements of the deque.
  • When erasing at either end of the deque, references to non-erased elements are not invalidated by erase, pop_front and pop_back.
  • A call to resize with a smaller size does not invalidate any references to non-erased elements.
  • A call to resize with a bigger size does not invalidate any references to elements of the deque.

[edit] Member types

Member type Definition
value_type T[edit]
allocator_type Allocator[edit]
size_type Unsigned integer type (usually std::size_t)[edit]
difference_type Signed integer type (usually std::ptrdiff_t)[edit]
reference value_type&[edit]
const_reference const value_type&[edit]
pointer

Allocator::pointer

(until C++11)

std::allocator_traits<Allocator>::pointer

(since C++11)
[edit]
const_pointer

Allocator::const_pointer

(until C++11)

std::allocator_traits<Allocator>::const_pointer

(since C++11)
[edit]
iterator LegacyRandomAccessIterator to value_type[edit]
const_iterator LegacyRandomAccessIterator to const value_type[edit]
reverse_iterator std::reverse_iterator<iterator>[edit]
const_reverse_iterator std::reverse_iterator<const_iterator>[edit]

[edit] Member functions

 constructs the deque
(public member function) [edit]
destructs the deque
(public member function) [edit]
assigns values to the container
(public member function) [edit]
assigns values to the container
(public member function) [edit]
(C++23)
 assigns a range of values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Element access
access specified element with bounds checking
(public member function) [edit]
access specified element
(public member function) [edit]
access the first element
(public member function) [edit]
access the last element
(public member function) [edit]
Iterators
(C++11)
 returns an iterator to the beginning
(public member function) [edit]
(C++11)
 returns an iterator to the end
(public member function) [edit]
(C++11)
 returns a reverse iterator to the beginning
(public member function) [edit]
(C++11)
 returns a reverse iterator to the end
(public member function) [edit]
Capacity
checks whether the container is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
returns the maximum possible number of elements
(public member function) [edit]
(DR*)
 reduces memory usage by freeing unused memory
(public member function) [edit]
Modifiers
clears the contents
(public member function) [edit]
inserts elements
(public member function) [edit]
(C++23)
 inserts a range of elements
(public member function) [edit]
(C++11)
 constructs element in-place
(public member function) [edit]
erases elements
(public member function) [edit]
adds an element to the end
(public member function) [edit]
(C++11)
 constructs an element in-place at the end
(public member function) [edit]
(C++23)
 adds a range of elements to the end
(public member function) [edit]
removes the last element
(public member function) [edit]
inserts an element to the beginning
(public member function) [edit]
(C++11)
 constructs an element in-place at the beginning
(public member function) [edit]
(C++23)
 adds a range of elements to the beginning
(public member function) [edit]
removes the first element
(public member function) [edit]
changes the number of elements stored
(public member function) [edit]
swaps the contents
(public member function) [edit]

[edit] 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 deques
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]
(C++20)
 erases all elements satisfying specific criteria
(function template) [edit]

Deduction guides

 (since C++17)

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_containers_ranges 202202L (C++23) Ranges construction and insertion for containers

[edit] Example

Run this code
#include <deque>
#include <iostream>
 
int main()
{
    // Create a deque containing integers
    std::deque<int> d = {7, 5, 16, 8};
 
    // Add an integer to the beginning and end of the deque
    d.push_front(13);
    d.push_back(25);
 
    // Iterate and print values of deque
    for (int n : d)
        std::cout << n << ' ';
    std::cout << '\n';
}

Output: 

13 7 5 16 8 25

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 230 C++98 T was not required to be CopyConstructible
(an element of type T might not be able to be constructed) 		T is also required to
be CopyConstructible

[edit] See also

 adapts a container to provide queue (FIFO data structure)
(class template) [edit]
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