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Difference between revisions of "cpp/types/rank"

From cppreference.com
< cpp‎ | types
m (simplified the example)
m (distinguish initialization between function call; should we use _v instead (C++17) or restore ::value (C++11)?)
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int main()
 
int main()
 
{
 
{
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     std::cout << std::rank<int>() << "\n\n";
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     std::cout << std::rank<int>{} << "\n\n";
 
   
 
   
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     std::cout << std::rank<int[5]>() << '\n';
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     std::cout << std::rank<int[5]>{} << '\n';
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     std::cout << std::rank<int[5][5]>() << '\n';
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     std::cout << std::rank<int[5][5]>{} << '\n';
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     std::cout << std::rank<int[][5][5]>() << '\n';
+
     std::cout << std::rank<int[][5][5]>{} << '\n';
 
}
 
}
 
  | output=
 
  | output=
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{{dsc inc | cpp/types/dsc remove_extent}}
 
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{{dsc inc | cpp/types/dsc remove_all_extents}}
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Revision as of 04:51, 10 January 2019

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Type support
 
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.

Contents

Helper variable template

template< class T >
inline 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>

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> {};

Example

Run this code
#include <iostream>
#include <type_traits>
 
int main()
{
    std::cout << std::rank<int>{} << "\n\n";
 
    std::cout << std::rank<int[5]>{} << '\n';
    std::cout << std::rank<int[5][5]>{} << '\n';
    std::cout << std::rank<int[][5][5]>{} << '\n';
}

Output: 

0
 
1
2
3

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]
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