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

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(Added LWG issue #355 DR.)
m (end iterator -> past-the-end iterator.)
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{{dr list item|wg=lwg|dr=322|std=C++98|before=the value types of {{tt|iterator}} and {{tt|const_iterator}} were not specified|after=specified as {{tt|T}}}}
 
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{{dr list item|wg=lwg|dr=355|std=C++98|before=calling {{tt|back()}} or {{tt|pop_back()}}<!-- they are optionally required in old standards --> would<br>decrement the end iterator directly|after=decrement a copy of<br>the end iterator instead}}
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{{dr list item|wg=lwg|dr=355|std=C++98|before=calling {{tt|back()}} or {{tt|pop_back()}}<!-- they are optionally required in old standards --> would<br>decrement the past-the-end iterator directly|after=decrement a copy of the<br>past-the-end iterator instead}}
 
{{dr list item|wg=lwg|dr=2263|std=C++11|before=the resolution of {{lwg|179}} was accidentally dropped in C++11|after=restored}}
 
{{dr list item|wg=lwg|dr=2263|std=C++11|before=the resolution of {{lwg|179}} was accidentally dropped in C++11|after=restored}}
 
{{dr list item|wg=lwg|dr=2839|std=C++11|before=self move assignment of standard containers was not allowed|after=allowed but the result is unspecifed}}
 
{{dr list item|wg=lwg|dr=2839|std=C++11|before=self move assignment of standard containers was not allowed|after=allowed but the result is unspecifed}}

Revision as of 22:37, 16 January 2023

 
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

  • T, an element type;
  • C, a Container type containing elements of type T;
  • a and b, objects of type C;
  • rv, a prvalue expression of type C.

Types

Name Type Requirements
value_type T CopyConstructible(until C++11)Erasable(since C++11)
reference T&
const_reference const T&
iterator iterator whose value type is T LegacyForwardIterator
convertible to const_iterator
const_iterator constant iterator whose value type is 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 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
(since C++11)		 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 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 276 C++98 T was required to be CopyAssignable T is required to be CopyConstructible
LWG 322 C++98 the value types of iterator and const_iterator were not specified specified as T
LWG 355 C++98 calling back() or pop_back() would
decrement the past-the-end iterator directly 		decrement a copy of the
past-the-end iterator instead
LWG 2263 C++11 the resolution of LWG issue 179 was accidentally dropped in C++11 restored
LWG 2839 C++11 self move assignment of standard containers was not allowed allowed but the result is unspecifed

See also

C++ documentation for Containers library
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