Difference between revisions of "cpp/container/mdspan"
From cppreference.com
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===Non-member functions=== | ===Non-member functions=== | ||
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===Notes=== | ===Notes=== | ||
− | {{feature test macro|__cpp_lib_mdspan}} | + | {{feature test macro|__cpp_lib_mdspan|std=C++23|value=202207L|{{tt|std::mdspan}}}} |
===Example=== | ===Example=== |
Revision as of 10:57, 11 November 2022
Defined in header <mdspan>
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template< class T, |
(since C++23) | |
std::mdspan
is a non-owning view into a contiguous sequence of objects that reinterprets it as a multidimensional array.
Contents |
Template parameters
T | - | element type; a complete object type that is neither an abstract class type nor an array type, |
Extents | - | specifies number of dimensions, their sizes, and which are known at compile time. Must be a specialization of std::extents |
LayoutPolicy | - | specifies how to convert multidimensional index to underlying 1D index (column-major 3D array, symmetric triangular 2D matrix, etc) |
AccessorPolicy | - | specifies how to convert underlying 1D index to a reference to T |
Member types
Member type | Definition |
extents_type
|
Extents
|
layout_type
|
LayoutPolicy
|
accessor_type
|
AccessorPolicy
|
mapping_type
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LayoutPolicy::mapping<Extents>
|
element_type
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T
|
value_type
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std::remove_cv_t<T>
|
index_type
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Extents::index_type
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size_type
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Extents::size_type
|
rank_type
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Extents::rank_type
|
data_handle_type
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AccessorPolicy::data_handle_type
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reference
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AccessorPolicy::reference
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Member functions
constructs an mdspan (public member function) | |
assigns an mdspan (public member function) | |
Element access | |
accesses an element at the specified multidimensional index (public member function) | |
Observers | |
returns the size of the multidimensional index space (public member function) | |
checks if the size of the index space is zero (public member function) | |
obtains the stride along the specified dimension (public member function) | |
obtains the extents object (public member function) | |
obtains the pointer to the underlying 1D sequence (public member function) | |
obtains the mapping object (public member function) | |
obtains the accessor policy object (public member function) | |
determines if this mdspan's mapping is unique (every combination of indices maps to a different underlying element) (public member function) | |
determines if this mdspan's mapping is exhaustive (every underlying element can be accessed with some combination of indices) (public member function) | |
determines if this mdspan's mapping is strided (in each dimension, incrementing an index jumps over the same number of underlying elements every time) (public member function) | |
[static] |
determines if this mdspan's layout mapping is always unique (public static member function) |
[static] |
determines if this mdspan's layout mapping is always exhaustive (public static member function) |
[static] |
determines if this mdspan's layout mapping is always strided (public static member function) |
Non-member functions
(C++23) |
specializes the std::swap algorithm for mdspan (function template) |
Helper types and templates
(C++23) |
a descriptor of a multidimensional index space of some rank (class template) |
(C++23)(C++26) |
convenience alias template for an all-dynamic std::extents (alias template) |
(C++23) |
row-major multidimensional array layout mapping policy; rightmost extent has stride 1 (class) |
(C++23) |
column-major multidimensional array layout mapping policy; leftmost extent has stride 1 (class) |
(C++23) |
a layout mapping policy with user-defined strides (class) |
Deduction guides
Notes
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_mdspan |
202207L | (C++23) | std::mdspan
|
Example
can be previewed at https://godbolt.org/z/PK7bccGr3
Run this code
#include <vector> #include <mdspan> #include <print> int main() { std::vector v = {1,2,3,4,5,6,7,8,9,10,11,12}; // View data as contiguous memory representing 2 rows of 6 ints each auto ms2 = std::mdspan(v.data(), 2, 6); // View the same data as a 3D array 2 x 3 x 2 auto ms3 = std::mdspan(v.data(), 2, 3, 2); // write data using 2D view for(size_t i=0; i != ms2.extent(0); i++) for(size_t j=0; j != ms2.extent(1); j++) ms2[i, j] = i*1000 + j; // read back using 3D view for(size_t i=0; i != ms3.extent(0); i++) { std::println("slice @ i = {}", i); for(size_t j=0; j != ms3.extent(1); j++) { for(size_t k=0; k != ms3.extent(2); k++) std::print("{} ", ms3[i, j, k]); std::println(""); } } }
Output:
slice @ i = 0 0 1 2 3 4 5 slice @ i = 1 1000 1001 1002 1003 1004 1005
See also
(C++20) |
a non-owning view over a contiguous sequence of objects (class template) |
numeric arrays, array masks and array slices (class template) |