Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/named req/Container"

From cppreference.com
< cpp‎ | named req
(LWG 2839)
Line 42: Line 42:
 
|{{c|a {{=}} b}}||C&||destroys or copy-assigns all elements of {{ttb|a}} from elements of {{ttb|b}}||Post: a == b||Linear
 
|{{c|a {{=}} b}}||C&||destroys or copy-assigns all elements of {{ttb|a}} from elements of {{ttb|b}}||Post: a == b||Linear
 
|-
 
|-
−
|{{c|a {{=}} rv}}||C&||destroys or move-assigns all elements of {{ttb|a}} from elements of {{ttb|rv}}||Post: a is equal to to the value rv had before this assignment||Linear
+
|{{c|a {{=}} rv}}||C&||destroys or move-assigns all elements of {{ttb|a}} from elements of {{ttb|rv}}||Post: if a and rv do not refer the same object, a is equal to to the value rv had before this assignment ||Linear
 
|-
 
|-
 
|{{c|a.~C()}}||void||destroys all elements of {{ttb|a}} and frees all memory||  ||Linear
 
|{{c|a.~C()}}||void||destroys all elements of {{ttb|a}} and frees all memory||  ||Linear
Line 54: Line 54:
 
|{{c|a.cend()}}{{mark since c++11}}||const_iterator||{{c|const_cast<const C&>(a).end()}}|| ||Constant
 
|{{c|a.cend()}}{{mark since c++11}}||const_iterator||{{c|const_cast<const C&>(a).end()}}|| ||Constant
 
|-
 
|-
−
|{{c|a {{==}} b}} || convertible to bool || {{c|std::equal(a.begin(), a.end(), b.begin(), b.end())}}{{mark since c++14}} ||Pre: T must be {{named req|EqualityComparable}} || Constant<ref>always linear for {{lc|std::forward_list}}</ref> if {{tt|a.size() !{{=}} b.size()}}, linear otherwise
+
|{{c|a {{==}} b}} || convertible to bool || {{rev inl|until=c++14|noborder=true|{{c|1=a.size() == b.size() &&
 +
std::equal(a.begin(), a.end(), b.begin()}}<br>}}{{rev inl|since=c++14|noborder=true|{{c|std::equal(a.begin(), a.end(), b.begin(), b.end())}}<br>}} ||Pre: T must be {{named req|EqualityComparable}} || Constant<ref>always linear for {{lc|std::forward_list}}</ref> if {{tt|a.size() !{{=}} b.size()}}, linear otherwise<!-- LWG2257 -->
 
|-
 
|-
 
|{{c|a !{{=}} b}} || convertible to bool || {{c|!(a {{==}} b)}} || || Linear
 
|{{c|a !{{=}} b}} || convertible to bool || {{c|!(a {{==}} b)}} || || Linear
Line 63: Line 64:
 
|{{c|swap(a, b)}} || void || {{c|a.swap(b)}} || || Constant<ref name="array"/>
 
|{{c|swap(a, b)}} || void || {{c|a.swap(b)}} || || Constant<ref name="array"/>
 
|-
 
|-
−
|{{c|a.size()}} || size_type || {{c|distance(a.begin(), a.end())}} || || Constant<ref name="should" />
+
|{{c|a.size()}} || size_type || {{c|std::distance(a.begin(), a.end())}} || || Constant<ref name="should" />
 
|-
 
|-
 
|{{c|a.max_size()}} || size_type || {{c|b.size()}} where {{ttb|b}} is the largest possible container || || Constant<ref name="should" />
 
|{{c|a.max_size()}} || size_type || {{c|b.size()}} where {{ttb|b}} is the largest possible container || || Constant<ref name="should" />
Line 74: Line 75:
 
|}
 
|}
  
−
{{rev begin}}
 
−
{{rev |since=c++14|
 
 
Given
 
Given
 
* {{tt|i}} and {{tt|j}}, objects of a container's {{tt|iterator}} type,
 
* {{tt|i}} and {{tt|j}}, objects of a container's {{tt|iterator}} type,
 
in the expressions {{c|i {{==}} j}}, {{c|i !{{=}} j}}, {{c|i < j}}, {{c|i <{{=}} j}}, {{c|i >{{=}} j}}, {{c|i > j}}, {{c|i - j}}, either or both may be replaced by an object of the container's {{tt|const_iterator}} type referring to the same element with no change in semantics.
 
in the expressions {{c|i {{==}} j}}, {{c|i !{{=}} j}}, {{c|i < j}}, {{c|i <{{=}} j}}, {{c|i >{{=}} j}}, {{c|i > j}}, {{c|i - j}}, either or both may be replaced by an object of the container's {{tt|const_iterator}} type referring to the same element with no change in semantics.
−
}}
 
−
{{rev end}}
 
  
 
===Container data races===
 
===Container data races===
Line 95: Line 92:
 
* {{named req|EqualityComparable}}
 
* {{named req|EqualityComparable}}
 
* {{named req|Destructible}}
 
* {{named req|Destructible}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=179|std=C++98|before={{tt|iterator}} and {{tt|const_iterator}} types might be incomparable|after=required to be comparable}}
 +
{{dr list item|wg=lwg|dr=2263|std=C++11|before=resolution of LWG179 was accidently dropped in C++11|after=restored}}
 +
{{dr list item|wg=lwg|dr=2839|std=C++11|before=self move assignment of containers was not allowed|after=allowed but the result is unspecifed}}
 +
{{dr list end}}
  
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Revision as of 05:50, 5 December 2020

 
C++
 
C++ named requirements
 

A Container is an object used to store other objects and taking care of the management of the memory used by the objects it contains.

Contents

Requirements

  • C container type;
  • T element type;
  • a, b objects of type C.
  • rv a prvalue expression of type C.

Types

name type notes
value_type T Eraseable
reference T&
const_reference const T&
iterator iterator pointing to T LegacyForwardIterator
convertible to const_iterator
const_iterator constant iterator pointing to T LegacyForwardIterator
difference_type signed integer must be the same as iterator_traits::difference_type for iterator and const_iterator
size_type unsigned integer large enough to represent all positive values of difference_type

Methods and operators

expression return type semantics conditions complexity
C() C creates an empty container Post: C().empty() == true Constant
C(a) C creates a copy of a Pre: T must be CopyInsertable
Post: a == C(a)		 Linear
C(rv)(since C++11) C moves rv Post: equal to to the value rv had before this construction Constant[1]
a = b C& destroys or copy-assigns all elements of a from elements of b Post: a == b Linear
a = rv C& destroys or move-assigns all elements of a from elements of rv Post: if a and rv do not refer the same object, a is equal to to the value rv had before this assignment Linear
a.~C() void destroys all elements of a and frees all memory Linear
a.begin() (const_)iterator Iterator to the first element of a Constant
a.end() (const_)iterator Iterator to one past the last element of a Constant
a.cbegin()(since C++11) const_iterator const_cast<const C&>(a).begin() Constant
a.cend()(since C++11) const_iterator const_cast<const C&>(a).end() Constant
a == b convertible to bool a.size() == b.size() &&
std::equal(a.begin(), a.end(), b.begin()
(until C++14)std::equal(a.begin(), a.end(), b.begin(), b.end())
(since C++14) 		Pre: T must be EqualityComparable Constant[2] if a.size() != b.size(), linear otherwise
a != b convertible to bool !(a == b) Linear
a.swap(b) void exchanges the values of a and b Constant[1][3]
swap(a, b) void a.swap(b) Constant[1]
a.size() size_type std::distance(a.begin(), a.end()) Constant[3]
a.max_size() size_type b.size() where b is the largest possible container Constant[3]
a.empty() convertible to bool a.begin() == a.end() Constant
notes
  1. ↑ 1.0 1.1 1.2 Linear for std::array
  2. ↑ always linear for std::forward_list
  3. ↑ 3.0 3.1 3.2 (until C++11) Not strictly constant

Given

  • i and j, objects of a container's iterator type,

in the expressions i == j, i != j, i < j, i <= j, i >= j, i > j, i - j, either or both may be replaced by an object of the container's const_iterator type referring to the same element with no change in semantics.

Container data races

see container thread safety

Other requirements

C
T

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 179 C++98 iterator and const_iterator types might be incomparable required to be comparable
LWG 2263 C++11 resolution of LWG179 was accidently dropped in C++11 restored
LWG 2839 C++11 self move assignment of containers was not allowed allowed but the result is unspecifed
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/named_req/Container&oldid=124758"