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Difference between revisions of "cpp/container/queue"

From cppreference.com
< cpp‎ | container
m (Minor fix.)
m (→‎Defect reports: a bit better, maybe.)
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     class Container {{=}} std::deque<T>
 
     class Container {{=}} std::deque<T>
 
> class queue;
 
> class queue;
−
}}  
+
}}
  
−
The {{tt|std::queue}} class is a container adaptor that gives the programmer the functionality of a queue - specifically, a FIFO (first-in, first-out) data structure.  
+
The {{tt|std::queue}} class is a container adaptor that gives the programmer the functionality of a queue - specifically, a FIFO (first-in, first-out) data structure.
  
 
The class template acts as a wrapper to the underlying container - only a specific set of functions is provided. The queue pushes the elements on the back of the underlying container and pops them from the front.
 
The class template acts as a wrapper to the underlying container - only a specific set of functions is provided. The queue pushes the elements on the back of the underlying container and pops them from the front.
Line 16: Line 16:
 
{{par|T|The type of the stored elements. {{rev inl|since=c++17|The behavior is undefined if {{tt|T}} is not the same type as {{tt|Container::value_type}}.}}}}
 
{{par|T|The type of the stored elements. {{rev inl|since=c++17|The behavior is undefined if {{tt|T}} is not the same type as {{tt|Container::value_type}}.}}}}
 
{{par|Container|The type of the underlying container to use to store the elements. The container must satisfy the requirements of {{named req|SequenceContainer}}. Additionally, it must provide the following functions with the usual semantics:
 
{{par|Container|The type of the underlying container to use to store the elements. The container must satisfy the requirements of {{named req|SequenceContainer}}. Additionally, it must provide the following functions with the usual semantics:
−
* {{tt|back()}}
+
* {{lc|back()}}
−
* {{tt|front()}}
+
* {{lc|front()}}
−
* {{tt|push_back()}}
+
* {{lc|push_back()}}
−
* {{tt|pop_front()}}
+
* {{lc|pop_front()}}
  
−
The standard containers {{lc|std::deque}} and {{lc|std::list}} satisfy these requirements.  
+
The standard containers {{lc|std::deque}} and {{lc|std::list}} satisfy these requirements.
 
}}{{par end}}
 
}}{{par end}}
  
 
===Member types===
 
===Member types===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc hitem | Member type | Definition}}
+
{{dsc hitem|Member type|Definition}}
−
{{dsc inc | cpp/container/dsc container_type | queue}}
+
{{dsc inc|cpp/container/dsc container_type|queue}}
−
{{dsc inc | cpp/container/dsc value_type | queue}}
+
{{dsc inc|cpp/container/dsc value_type|queue}}
−
{{dsc inc | cpp/container/dsc size_type | queue}}
+
{{dsc inc|cpp/container/dsc size_type|queue}}
−
{{dsc inc | cpp/container/dsc reference | queue}}
+
{{dsc inc|cpp/container/dsc reference|queue}}
−
{{dsc inc | cpp/container/dsc const_reference | queue}}
+
{{dsc inc|cpp/container/dsc const_reference|queue}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Member functions===
 
===Member functions===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc constructor | queue}}
+
{{dsc inc|cpp/container/dsc constructor|queue}}
−
{{dsc inc | cpp/container/dsc destructor | queue}}
+
{{dsc inc|cpp/container/dsc destructor|queue}}
−
{{dsc inc | cpp/container/dsc operator{{=}} | queue}}
+
{{dsc inc|cpp/container/dsc operator{{=}}|queue}}
  
−
{{dsc h2 | Element access}}
+
{{dsc h2|Element access}}
−
{{dsc inc | cpp/container/dsc front | queue}}
+
{{dsc inc|cpp/container/dsc front|queue}}
−
{{dsc inc | cpp/container/dsc back | queue}}
+
{{dsc inc|cpp/container/dsc back|queue}}
  
−
{{dsc h2 | Capacity}}
+
{{dsc h2|Capacity}}
−
{{dsc inc | cpp/container/dsc empty | queue}}
+
{{dsc inc|cpp/container/dsc empty|queue}}
−
{{dsc inc | cpp/container/dsc size | queue}}
+
{{dsc inc|cpp/container/dsc size|queue}}
  
−
{{dsc h2 | Modifiers}}
+
{{dsc h2|Modifiers}}
−
{{dsc inc | cpp/container/dsc push | queue}}
+
{{dsc inc|cpp/container/dsc push|queue}}
−
{{dsc inc | cpp/container/dsc emplace | queue}}
+
{{dsc inc|cpp/container/dsc emplace|queue}}
−
{{dsc inc | cpp/container/dsc pop | queue}}
+
{{dsc inc|cpp/container/dsc pop|queue}}
−
{{dsc inc | cpp/container/dsc swap | queue}}
+
{{dsc inc|cpp/container/dsc swap|queue}}
  
−
{{dsc h1 | Member objects}}
+
{{dsc h1|Member objects}}
−
{{dsc inc | cpp/container/dsc c | queue}}
+
{{dsc inc|cpp/container/dsc c|queue}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Non-member functions===
 
===Non-member functions===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc operator_cmp | queue}}
+
{{dsc inc|cpp/container/dsc operator_cmp|queue}}
−
{{dsc inc | cpp/container/dsc swap2 | queue}}
+
{{dsc inc|cpp/container/dsc swap2|queue}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Helper classes===
 
===Helper classes===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc uses_allocator | queue}}
+
{{dsc inc|cpp/container/dsc uses_allocator|queue}}
 
{{dsc end}}
 
{{dsc end}}
  
−
===[[cpp/container/queue/deduction guides|Deduction guides]]{{mark since c++17}}===
+
==={{rl|deduction guides|Deduction guides}}{{mark since c++17}}===
  
 
===Defect reports===
 
===Defect reports===
 
{{dr list begin}}
 
{{dr list begin}}
−
{{dr list item|wg=lwg|dr=307|std=C++98|before={{tt|std::queue}} did not support containers using proxy<br>reference types<ref>Such as containers similar to {{ltt|cpp/container/vector bool|std::vector<bool>}} with additional support of {{tt|pop_front()}}. The resolution of this DR added support of {{ltt|cpp/container/vector bool|std::vector<bool>}} for {{lc|std::stack}} and {{lc|std::priority_queue}}. The changes involving {{tt|std::queue}} is for maintaing consistency.</ref> in place of ({{tt|const}}) {{tt|value_type&}}|after=supported}}
+
{{dr list item|wg=lwg|dr=307|std=C++98|before={{tt|std::queue}} did not support containers using proxy<br>reference types<ref>Such as containers similar to {{ltt|cpp/container/vector bool|std::vector<bool>}} with additional support of {{tt|pop_front()}}. The resolution of this DR added support of {{ltt|cpp/container/vector bool|std::vector<bool>}} for {{lc|std::stack}} and {{lc|std::priority_queue}}. The changes involving {{tt|std::queue}} are for maintaining consistency.</ref> in place of ({{tt|const}}) {{tt|value_type&}}|after=supported}}
 
{{dr list end}}
 
{{dr list end}}
 
<references/>
 
<references/>

Revision as of 07:52, 10 January 2023

 
C++
 
Containers library
 
std::queue
 
Defined in header <queue>
template<

    class T,
    class Container = std::deque<T>

> class queue;

The std::queue class is a container adaptor that gives the programmer the functionality of a queue - specifically, a FIFO (first-in, first-out) data structure.

The class template acts as a wrapper to the underlying container - only a specific set of functions is provided. The queue pushes the elements on the back of the underlying container and pops them from the front.

Contents

Template parameters

T - The type of the stored elements. The behavior is undefined if T is not the same type as Container::value_type.(since C++17)
Container - The type of the underlying container to use to store the elements. The container must satisfy the requirements of SequenceContainer. Additionally, it must provide the following functions with the usual semantics:

The standard containers std::deque and std::list satisfy these requirements.

Member types

Member type Definition
container_type Container[edit]
value_type Container::value_type[edit]
size_type Container::size_type[edit]
reference Container::reference[edit]
const_reference Container::const_reference[edit]

Member functions

 constructs the queue
(public member function) [edit]
destructs the queue
(public member function) [edit]
assigns values to the container adaptor
(public member function) [edit]
Element access
access the first element
(public member function) [edit]
access the last element
(public member function) [edit]
Capacity
checks whether the container adaptor is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
Modifiers
inserts element at the end
(public member function) [edit]
(C++11)
 constructs element in-place at the end
(public member function) [edit]
removes the first element
(public member function) [edit]
(C++11)
 swaps the contents
(public member function) [edit]

Member objects

Container c
 the underlying container
(protected member object) [edit]

Non-member functions

(C++20)
 lexicographically compares the values of two queues
(function template) [edit]
(C++11)
 specializes the std::swap algorithm
(function template) [edit]

Helper classes

(C++11)
 specializes the std::uses_allocator type trait
(class template specialization) [edit]

Deduction guides(since C++17)

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 307 C++98 std::queue did not support containers using proxy
reference types[1] in place of (const) value_type& 		supported
  1. ↑ Such as containers similar to std::vector<bool> with additional support of pop_front(). The resolution of this DR added support of std::vector<bool> for std::stack and std::priority_queue. The changes involving std::queue are for maintaining consistency.

See also

 double-ended queue
(class template) [edit]
doubly-linked list
(class template) [edit]
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