Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/types/rank"

From cppreference.com
< cpp‎ | types
(formatting)
m (-`inline`: CWG2387; fmt.)
 
(25 intermediate revisions by 10 users not shown)
Line 1: Line 1:
 
{{cpp/title|rank}}
 
{{cpp/title|rank}}
−
{{cpp/types/sidebar}}
+
{{cpp/meta/navbar}}
−
{{ddcl list begin}}
+
{{ddcl|header=type_traits|since=c++11|
−
{{ddcl list header | type_traits}}
+
−
{{ddcl list item | notes={{mark c++11 feature}} | 1=
+
 
template< class T >
 
template< class T >
 
struct rank;
 
struct rank;
 
}}
 
}}
−
{{ddcl list end}}
 
  
−
If {{tt|T}} is an array type, provides the member constant {{tt|value}} equal to the number of dimensions of the array. For any other type, {{tt|value}} is 0.
+
If {{tt|T}} is an array type, provides the member constant {{c|value}} equal to the number of dimensions of the array. For any other type, {{c|value}} is {{c|0}}.
  
−
===Member objects===
+
{{cpp/types/nospec|v}}
−
{{tdcl list begin}}
+
−
{{tdcl list hitem | Name | Definition}}
+
−
{{tdcl list item | {{tt|value}} | the number of dimensions of {{tt|T}} or zero}}
+
−
{{tdcl list end}}
+
  
−
===Equivalent definition===
+
===Helper variable template===
−
{{eq fun cpp
+
{{ddcl|since=c++17|1=
−
| 1=
+
template< class T >
 +
constexpr std::size_t rank_v = rank<T>::value;
 +
}}
 +
 
 +
{{cpp/types/integral_constant/inherit2|the number of dimensions of {{tt|T}} or zero|std::size_t}}
 +
 
 +
===Possible implementation===
 +
{{eq fun
 +
|1=
 
template<class T>
 
template<class T>
−
struct rank : std::integral_constant<std::size_t, 0> {};
+
struct rank : public std::integral_constant<std::size_t, 0> {};
  
 
template<class T>
 
template<class T>
 
struct rank<T[]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};
 
struct rank<T[]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};
  
−
template<class T, size_t N >
+
template<class T, std::size_t N>
 
struct rank<T[N]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};
 
struct rank<T[N]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};
 
}}
 
}}
  
 
===Example===
 
===Example===
−
{{example cpp
+
{{example
−
|
+
|code=
−
| code=
+
−
#include <iostream>
+
 
#include <type_traits>
 
#include <type_traits>
  
−
template<typename A>
+
static_assert(std::rank<int>{} == 0);
−
void print_dim(const A&)
+
static_assert(std::rank<int[5]>{} == 1);
−
{
+
static_assert(std::rank<int[5][5]>{} == 2);
−
    std::cout << "The array has " << std::rank<A>::value << " dimensions\n";
+
static_assert(std::rank<int[][5][5]>{} == 3);
−
}
+
  
 
int main()
 
int main()
 
{
 
{
−
     int a[1][2][3];
+
     [[maybe_unused]] int ary[][3] = {<!---->{1, 2, 3}<!---->};
−
     print_dim(a);
+
 
−
     print_dim(a[0]);
+
    // The rank of reference type, e.g., ary[0], that is int(&)[3], is 0:
 +
    static_assert(std::rank_v<decltype(ary[0])> == 0);
 +
     static_assert(std::is_same_v<decltype(ary[0]), int(&)[3]>);
 +
 
 +
     // The solution is to remove the reference type.
 +
    static_assert(std::rank_v<std::remove_cvref_t<decltype(ary[0])>> == 1);
 
}
 
}
−
| output=
 
−
The array has 3 dimensions
 
−
The array has 2 dimensions
 
 
}}
 
}}
  
 
===See also===
 
===See also===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/types/dcl list is_array}}
+
{{dsc inc|cpp/types/dsc is_array}}
−
{{dcl list template | cpp/types/dcl list extent}}
+
{{dsc inc|cpp/types/dsc extent}}
−
{{dcl list template | cpp/types/dcl list remove_extent}}
+
{{dsc inc|cpp/types/dsc remove_extent}}
−
{{dcl list template | cpp/types/dcl list remove_all_extents}}
+
{{dsc inc|cpp/types/dsc remove_all_extents}}
−
{{dcl list end}}
+
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 09:19, 24 September 2024

 
C++
 
Metaprogramming library
Type traits
Type categories
(C++11)
(C++14)  
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)  
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Type properties
(C++11)
(C++11)
(C++11)
(C++11)
(C++14)
(C++11)
(C++17)
(C++23)
(C++11)
(C++11)
(C++11)
(C++11)(until C++20*)
(C++11)(deprecated in C++20)
(C++11)
(C++11)
(C++20)
(C++20)
(C++23)
(C++17)
Type trait constants
(C++11)(C++17)(C++11)(C++11)
Metafunctions
(C++17)
(C++17)
(C++17)
Supported operations
Relationships and property queries
Type modifications
(C++11)(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Type transformations
(C++11)(deprecated in C++23)
(C++11)(deprecated in C++23)
(C++11)
(C++20)
(C++11)
(C++17)

(C++11)
(C++11)
(C++20)
(C++11)
(C++11)(until C++20*)(C++17)
(C++20)
Compile-time rational arithmetic
Compile-time integer sequences
(C++14)
 
Defined in header <type_traits>
template< class T >
struct rank;
 (since C++11)

If T is an array type, provides the member constant value equal to the number of dimensions of the array. For any other type, value is ​0​.

If the program adds specializations for std::rank or std::rank_v(since C++17), the behavior is undefined.

Contents

[edit] Helper variable template

template< class T >
constexpr std::size_t rank_v = rank<T>::value;
 (since C++17)

Inherited from std::integral_constant

Member constants

value
[static]
 the number of dimensions of T or zero
(public static member constant)

Member functions

operator std::size_t
 converts the object to std::size_t, returns value
(public member function)
operator()
(C++14)
 returns value
(public member function)

Member types

Type Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

[edit] Possible implementation

template<class T>
struct rank : public std::integral_constant<std::size_t, 0> {};
 
template<class T>
struct rank<T[]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};
 
template<class T, std::size_t N>
struct rank<T[N]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};

[edit] Example

Run this code
#include <type_traits>
 
static_assert(std::rank<int>{} == 0);
static_assert(std::rank<int[5]>{} == 1);
static_assert(std::rank<int[5][5]>{} == 2);
static_assert(std::rank<int[][5][5]>{} == 3);
 
int main()
{
    [[maybe_unused]] int ary[][3] = {{1, 2, 3}};
 
    // The rank of reference type, e.g., ary[0], that is int(&)[3], is 0:
    static_assert(std::rank_v<decltype(ary[0])> == 0);
    static_assert(std::is_same_v<decltype(ary[0]), int(&)[3]>);
 
    // The solution is to remove the reference type.
    static_assert(std::rank_v<std::remove_cvref_t<decltype(ary[0])>> == 1);
}

[edit] See also

(C++11)
 checks if a type is an array type
(class template) [edit]
(C++11)
 obtains the size of an array type along a specified dimension
(class template) [edit]
(C++11)
 removes one extent from the given array type
(class template) [edit]
(C++11)
 removes all extents from the given array type
(class template) [edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/types/rank&oldid=176457"