Difference between revisions of "cpp/container/mdspan"
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Revision as of 14:15, 27 March 2023
| Defined in header <mdspan>
|
||
| 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
|
LayoutPolicy::mapping<Extents>
|
element_type
|
T
|
value_type
|
std::remove_cv_t<T>
|
index_type
|
Extents::index_type
|
size_type
|
Extents::size_type
|
rank_type
|
Extents::rank_type
|
data_handle_type
|
AccessorPolicy::data_handle_type
|
reference
|
AccessorPolicy::reference
|
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) |
