std::span<T,Extent>:: span

From cppreference.com
C++
Containers library
std::span
constexpr span ( ) noexcept ;
(1) (since C++20)
template < class It >

explicit ( extent ! = std:: dynamic_extent )

constexpr span ( It first, size_type count ) ;
(2) (since C++20)
template < class It, class End >

explicit ( extent ! = std:: dynamic_extent )

constexpr span ( It first, End last ) ;
(3) (since C++20)
template < std:: size_t N >
constexpr span ( std:: type_identity_t < element_type > ( & arr ) [ N ] ) noexcept ;
(4) (since C++20)
template < class U, std:: size_t N >
constexpr span ( std:: array < U, N > & arr ) noexcept ;
(5) (since C++20)
template < class U, std:: size_t N >
constexpr span ( const std:: array < U, N > & arr ) noexcept ;
(6) (since C++20)
template < class R >

explicit ( extent ! = std:: dynamic_extent )

constexpr span ( R && range ) ;
(7) (since C++20)
explicit ( extent ! = std:: dynamic_extent )
constexpr span ( std:: initializer_list < value_type > il ) noexcept ;
(8) (since C++26)
template < class U, std:: size_t N >

explicit ( extent ! = std:: dynamic_extent && N == std:: dynamic_extent )

constexpr span ( const std:: span < U, N > & source ) noexcept ;
(9) (since C++20)
constexpr span ( const span & other ) noexcept = default ;
(10) (since C++20)

Constructs a span .

1) Constructs an empty span whose data ( ) == nullptr and size ( ) == 0 .
2) Constructs a span that is a view over the range [ first , first + count ) ; the resulting span has data ( ) == std:: to_address ( first ) and size ( ) == count .
  • The behavior is undefined if [ first , first + count ) is not a valid range, if It does not actually model contiguous_iterator , or if extent ! = std:: dynamic_extent && count ! = extent .
  • This overload participates in overload resolution only if
3) Constructs a span that is a view over the range [ first , last ) ; the resulting span has data ( ) == std:: to_address ( first ) and size ( ) == last - first .
4-6) Constructs a span that is a view over the array arr ; the resulting span has size ( ) == N and data ( ) == std:: data ( arr ) .
  • These overloads participate in overload resolution only if extent == std:: dynamic_extent || N == extent is true and the conversion from std:: remove_pointer_t < decltype ( data ( arr ) ) > to element_type is at most a qualification conversion.
7) Constructs a span that is a view over the range range ; the resulting span has size ( ) == std :: ranges:: size ( range ) and data ( ) == std :: ranges:: data ( range ) .
8) Constructs a span that is a view over the initializer list il ; the resulting span has size ( ) == il. size ( ) and data ( ) == il. begin ( ) .
  • The behavior is undefined if both extent ! = dynamic_extent and il. size ( ) ! = extent are true .
  • This overload participates in overload resolution only if std:: is_const_v < element_type > is true .
9) Converting constructor from another span source ; the resulting span has size ( ) == source. size ( ) and data ( ) == source. data ( ) .
  • The behavior is undefined if both extent ! = dynamic_extent and source. size ( ) ! = extent are true .
  • This overload participates in overload resolution only if at least one of extent == std:: dynamic_extent , N == std:: dynamic_extent and N == extent is true and the conversion from U to element_type is at most a qualification conversion.
10) Defaulted copy constructor copies the size and data pointer; the resulting span has size ( ) == other. size ( ) and data ( ) == other. data ( ) .

Parameters

first - iterator to the first element of the sequence
count - number of elements in the sequence
last - iterator past the last element of the sequence or another sentinel
arr - array to construct a view for
range - range to construct a view for
source - another span to convert from
other - another span to copy from

Exceptions

2) Throws nothing.
3) Throws what and when last - first throws.
7) Throws what and when std :: ranges:: size ( r ) and std :: ranges:: data ( r ) throw.

Notes

Feature-test macro Value Std Feature
__cpp_lib_span_initializer_list 202311L (C++26) Constructing std::span from a std::initializer_list , ( 8 )

Example

Run this code 
#include <array>
#include <iostream>
#include <span>
#include <vector>
 
void print_span(std::span<const int> s)
{
    for (int n : s)
        std::cout << n << ' ';
    std::cout << '\n';
}
 
int main()
{
    int c[]{1, 2, 3};
    print_span(c); // constructs from array
 
    std::array a{4, 5, 6};
    print_span(a); // constructs from std::array
 
    std::vector v{7, 8, 9};
    print_span(v); // constructs from std::vector
 
#if __cpp_lib_span_initializer_list
    print_span({0, 1, 2}); // constructs from initializer_list
#else
    print_span({{0, 1, 2}}); // ditto, a workaround
#endif
}

Output: 

1 2 3 
4 5 6
7 8 9
0 1 2

See also

direct access to the underlying contiguous storage
(public member function)
returns the number of elements
(public member function)
assigns a span
(public member function)
(C++17) (C++20)
returns the size of a container or array
(function template)
(C++17)
obtains the pointer to the underlying array
(function template)
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