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Difference between revisions of "cpp/iterator/data"

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< cpp‎ | iterator
(Undo revision 158911 by SmartDev (talk))
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{{cpp/title| data}}
+
{{cpp/title|data}}
 
{{cpp/iterator/navbar}}
 
{{cpp/iterator/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{dcl header | iterator}}
+
{{dcl header|array}}
−
{{dcl header | array}}
+
{{dcl header|deque}}
−
{{dcl header | deque}}
+
{{dcl header|forward_list}}
−
{{dcl header | forward_list}}
+
{{dcl header|iterator}}
−
{{dcl header | list}}
+
{{dcl header|list}}
−
{{dcl header | map}}
+
{{dcl header|map}}
−
{{dcl header | regex}}
+
{{dcl header|regex}}
−
{{dcl header | set}}
+
{{dcl header|set}}
−
{{dcl header | string}}
+
{{dcl sep}}
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{{dcl header | unordered_map}}
+
{{dcl header|span|notes={{mark since c++20}}}}
−
{{dcl header | unordered_set}}
+
{{dcl sep}}
−
{{dcl header | vector}}
+
{{dcl header|string}}
−
{{dcl | num=1 | since=c++17 |
+
{{dcl header|string_view}}
−
template <class C>  
+
{{dcl header|unordered_map}}
−
constexpr auto data(C& c) -> decltype(c.data());
+
{{dcl header|unordered_set}}
 +
{{dcl header|vector}}
 +
{{dcla|num=1|since=c++17|
 +
template< class C >
 +
constexpr auto data( C& c ) -> decltype(c.data());
 
}}
 
}}
−
{{dcl | num=2 | since=c++17 |
+
{{dcla|num=2|since=c++17|
−
template <class C>  
+
template< class C >
−
constexpr auto data(const C& c) -> decltype(c.data());
+
constexpr auto data( const C& c ) -> decltype(c.data());
 
}}
 
}}
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{{dcl | num=3 | since=c++17 |
+
{{dcla|num=3|since=c++17|
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template <class T, std::size_t N>  
+
template< class T, std::size_t N >
−
constexpr T* data(T (&array)[N]) noexcept;
+
constexpr T* data( T (&array)[N] ) noexcept;
 
}}
 
}}
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{{dcl | num=4 | since=c++17 |
+
{{dcla|num=4|since=c++17|
−
template <class E>
+
template< class E >
−
constexpr const E* data(std::initializer_list<E> il) noexcept;
+
constexpr const E* data( std::initializer_list<E> il ) noexcept;
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Returns a pointer to the block of memory containing the elements of the container.
+
Returns a pointer to the block of memory containing the elements of the range.
  
−
@1,2@ returns {{c|c.empty()}}
+
@1,2@ returns {{c|c.data()}}
 
@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}}
−
{{par | c | a container with a {{c|data()}} method}}
+
{{par|c|a container or view with a {{c|data()}} member function}}
−
{{par | array | an array of arbitrary type}}
+
{{par|array|an array of arbitrary type}}
−
{{par | il | an initializer list}}
+
{{par|il|an initializer list}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
A pointer to the block of memory containing the elements of the container.
+
A pointer to the block of memory containing the elements of the range.
  
 
===Exceptions===
 
===Exceptions===
−
@3,4@ {{noexcept}}
+
@1@ {{cpp/impldef exception item}}
 +
 
 +
===Notes===
 +
The overload for {{lc|std::initializer_list}} is necessary because it does not have a member function {{tt|data}}.
 +
 
 +
{{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===
−
{{eq fun
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{{eq impl
−
| 1=
+
|ver1=1|1=
−
template <class C>  
+
template <class C>
−
constexpr auto data(C& c) -> decltype(c.data());
+
constexpr auto data(C& c) -> decltype(c.data())
 
{
 
{
 
     return c.data();
 
     return c.data();
 
}
 
}
−
| 2=
+
|ver2=2|2=
−
template <class C>  
+
template <class C>
−
constexpr auto data(const C& c) -> decltype(c.data());
+
constexpr auto data(const C& c) -> decltype(c.data())
 
{
 
{
 
     return c.data();
 
     return c.data();
 
}
 
}
−
| 3=
+
|ver3=3|3=
 
template <class T, std::size_t N>
 
template <class T, std::size_t N>
−
constexpr T* data(T (&array)[N]) noexcept;
+
constexpr T* data(T (&array)[N]) noexcept
 
{
 
{
 
     return array;
 
     return array;
 
}
 
}
−
|4=
+
|ver4=4|4=
−
template <class E>  
+
template <class E>
−
constexpr const E* data(std::initializer_list<E> il) noexcept;
+
constexpr const E* data(std::initializer_list<E> il) noexcept
 
{
 
{
 
     return il.begin();
 
     return il.begin();
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===Example===
 
===Example===
−
{{example}}
+
{{example
 +
|code=
 +
#include <cstring>
 +
#include <iostream>
 +
#include <string>
 +
 
 +
int main()
 +
{
 +
    std::string s{"Hello world!\n"};
 +
 
 +
    char a[20]; // storage for a C-style string
 +
    std::strcpy(a, std::data(s));
 +
    // [s.data(), s.data() + s.size()] is guaranteed to be an NTBS since C++11
 +
 
 +
    std::cout << a;
 +
}
 +
|output=
 +
Hello world!
 +
}}
 +
 
 +
===See also===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/ranges/dsc data}}
 +
{{dsc inc|cpp/ranges/dsc cdata}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|es|ja|ru|zh}}

Revision as of 15:25, 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 <array>
Defined in header <deque>
Defined in header <forward_list>
Defined in header <iterator>
Defined in header <list>
Defined in header <map>
Defined in header <regex>
Defined in header <set>
Defined in header <span>
(since C++20)
Defined in header <string>
Defined in header <string_view>
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 range.

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

Contents

Parameters

c - a container or view with a data() member function
array - an array of arbitrary type
il - an initializer list

Return value

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

Exceptions

1) May throw implementation-defined exceptions.

Notes

The overload for std::initializer_list is necessary because it does not have a member function data.

Feature-test macro Value Std Feature
__cpp_lib_nonmember_container_access 201411L (C++17) std::size(), std::data(), and std::empty()

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

Run this code
#include <cstring>
#include <iostream>
#include <string>
 
int main()
{
    std::string s{"Hello world!\n"};
 
    char a[20]; // storage for a C-style string
    std::strcpy(a, std::data(s));
    // [s.data(), s.data() + s.size()] is guaranteed to be an NTBS since C++11
 
    std::cout << a;
}

Output: 

Hello world!

See also

(C++20)
 obtains a pointer to the beginning of a contiguous range
(customization point object)[edit]
(C++20)
 obtains a pointer to the beginning of a read-only contiguous range
(customization point object)[edit]
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