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Difference between revisions of "cpp/iterator/data"

From cppreference.com
< cpp‎ | iterator
(→‎Synopsis: emphasizes the revision's target header. (?))
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{{cpp/title|data}}
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{{cpp/title| data}}
 
{{cpp/iterator/navbar}}
 
{{cpp/iterator/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{dcl header|array}}
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{{dcl header | iterator}}
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{{dcl header|deque}}
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{{dcl header | array}}
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{{dcl header|forward_list}}
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{{dcl header | deque}}
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{{dcl header|iterator}}
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{{dcl header | forward_list}}
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{{dcl header|list}}
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{{dcl header | list}}
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{{dcl header|map}}
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{{dcl header | map}}
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{{dcl header|regex}}
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{{dcl header | regex}}
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{{dcl header|set}}
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{{dcl header | set}}
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{{dcl sep}}
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{{dcl header | string}}
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{{dcl header|span|notes={{mark since c++20}}}}
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{{dcl header | unordered_map}}
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{{dcl sep}}
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{{dcl header | unordered_set}}
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{{dcl header|string}}
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{{dcl header | vector}}
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{{dcl header|string_view}}
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{{dcl | num=1 | since=c++17 |
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{{dcl header|unordered_map}}
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template <class C>  
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{{dcl header|unordered_set}}
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constexpr auto data(C& c) -> decltype(c.data());
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{{dcl header|vector}}
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−
{{dcla|num=1|since=c++17|
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−
template< class C >
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constexpr auto data( C& c ) -> decltype(c.data());
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}}
 
}}
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{{dcla|num=2|since=c++17|
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{{dcl | num=2 | since=c++17 |
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template< class C >
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template <class C>  
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constexpr auto data( const C& c ) -> decltype(c.data());
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constexpr auto data(const C& c) -> decltype(c.data());
 
}}
 
}}
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{{dcla|num=3|since=c++17|
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{{dcl | num=3 | since=c++17 |
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template< class T, std::size_t N >
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template <class T, std::size_t N>  
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constexpr T* data( T (&array)[N] ) noexcept;
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constexpr T* data(T (&array)[N]) noexcept;
 
}}
 
}}
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{{dcla|num=4|since=c++17|
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{{dcl | num=4 | since=c++17 |
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template< class E >
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template <class E>
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constexpr const E* data( std::initializer_list<E> il ) noexcept;
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constexpr const E* data(std::initializer_list<E> il) noexcept;
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
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Returns a pointer to the block of memory containing the elements of the range.
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Returns a pointer to the block of memory containing the elements of the container.
  
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@1,2@ returns {{c|c.data()}}
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@1,2@ returns {{c|c.empty()}}
 
@3@ returns {{c|array}}
 
@3@ returns {{c|array}}
 
@4@ returns {{c|il.begin()}}
 
@4@ returns {{c|il.begin()}}
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===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
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{{par|c|a container or view with a {{c|data()}} member function}}
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{{par | c | a container with a {{c|data()}} method}}
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{{par|array|an array of arbitrary type}}
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{{par | array | an array of arbitrary type}}
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{{par|il|an initializer list}}
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{{par | il | an initializer list}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
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A pointer to the block of memory containing the elements of the range.
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A pointer to the block of memory containing the elements of the container.
  
 
===Exceptions===
 
===Exceptions===
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@1@ {{cpp/impldef exception item}}
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@3,4@ {{noexcept}}
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+
−
===Notes===
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The overload for {{lc|std::initializer_list}} is necessary because it does not have a member function {{tt|data}}.
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−
 
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{{feature test macro|__cpp_lib_nonmember_container_access|{{lc|std::size()}}, {{tt|std::data()}}, and {{lc|std::empty()}}|value=201411L|std=C++17}}
+
  
 
===Possible implementation===
 
===Possible implementation===
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{{eq impl
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{{eq fun
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|ver1=1|1=
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| 1=
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template <class C>
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template <class C>  
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constexpr auto data(C& c) -> decltype(c.data())
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constexpr auto data(C& c) -> decltype(c.data());
 
{
 
{
 
     return c.data();
 
     return c.data();
 
}
 
}
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|ver2=2|2=
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| 2=
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template <class C>
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template <class C>  
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constexpr auto data(const C& c) -> decltype(c.data())
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constexpr auto data(const C& c) -> decltype(c.data());
 
{
 
{
 
     return c.data();
 
     return c.data();
 
}
 
}
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|ver3=3|3=
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| 3=
 
template <class T, std::size_t N>
 
template <class T, std::size_t N>
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constexpr T* data(T (&array)[N]) noexcept
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constexpr T* data(T (&array)[N]) noexcept;
 
{
 
{
 
     return array;
 
     return array;
 
}
 
}
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|ver4=4|4=
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|4=
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template <class E>
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template <class E>  
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constexpr const E* data(std::initializer_list<E> il) noexcept
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constexpr const E* data(std::initializer_list<E> il) noexcept;
 
{
 
{
 
     return il.begin();
 
     return il.begin();
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===Example===
 
===Example===
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{{example
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{{example}}
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|code=
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#include <cstring>
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#include <iostream>
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#include <string>
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int main()
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{
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    std::string s{"Hello world!\n"};
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−
 
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    char a[20]; // storage for a C-style string
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    std::strcpy(a, std::data(s));
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    // [s.data(), s.data() + s.size()] is guaranteed to be an NTBS since C++11
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    std::cout << a;
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}
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|output=
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Hello world!
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}}
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===See also===
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{{dsc begin}}
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{{dsc inc|cpp/ranges/dsc data}}
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{{dsc inc|cpp/ranges/dsc cdata}}
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{{dsc end}}
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−
 
+
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{{langlinks|es|ja|ru|zh}}
+

Revision as of 14:48, 12 September 2023

 
C++
 
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
Iterator adaptors
Range access
(C++11)(C++14)
(C++14)(C++14)  
(C++11)(C++14)
(C++14)(C++14)  
(C++17)(C++20)
(C++17)
data
(C++17)
 
Defined in header <iterator>
Defined in header <array>
Defined in header <deque>
Defined in header <forward_list>
Defined in header <list>
Defined in header <map>
Defined in header <regex>
Defined in header <set>
Defined in header <string>
Defined in header <unordered_map>
Defined in header <unordered_set>
Defined in header <vector>
template <class C>
constexpr auto data(C& c) -> decltype(c.data());
 (1) (since C++17)
template <class C>
constexpr auto data(const C& c) -> decltype(c.data());
 (2) (since C++17)
template <class T, std::size_t N>
constexpr T* data(T (&array)[N]) noexcept;
 (3) (since C++17)
template <class E>
constexpr const E* data(std::initializer_list<E> il) noexcept;
 (4) (since C++17)

Returns a pointer to the block of memory containing the elements of the container.

1,2) returns c.empty()
3) returns array
4) returns il.begin()

Contents

Parameters

c - a container with a data() method
array - an array of arbitrary type
il - an initializer list

Return value

A pointer to the block of memory containing the elements of the container.

Exceptions

3,4)
noexcept specification:  
noexcept
  

Possible implementation

First version 
template <class C> 
constexpr auto data(C& c) -> decltype(c.data());
{
    return c.data();
}
Second version 
template <class C> 
constexpr auto data(const C& c) -> decltype(c.data());
{
    return c.data();
}
Third version 
template <class T, std::size_t N>
constexpr T* data(T (&array)[N]) noexcept;
{
    return array;
}
Fourth version 
template <class E> 
constexpr const E* data(std::initializer_list<E> il) noexcept;
{
    return il.begin();
}

Example

This section is incomplete
Reason: no example
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