std::rank

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Metaprogramming library

Type traits
Type categories is_void (C++11) is_null_pointer (C++11)(DR*) is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11) is_reference (C++11)  is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11)   is_fundamental (C++11) is_arithmetic (C++11) is_lvalue_reference (C++11) is_rvalue_reference (C++11) is_member_pointer (C++11) is_member_object_pointer (C++11) is_member_function_pointer (C++11) Type properties is_const (C++11) is_volatile (C++11) is_empty (C++11) is_polymorphic (C++11) is_final (C++14) is_abstract (C++11) is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (C++11)(deprecated in C++26) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11)(until C++20*) is_pod (C++11)(deprecated in C++20) is_signed (C++11) is_unsigned (C++11) is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17) Type trait constants integral_constantbool_constanttrue_typefalse_type (C++11)(C++17)(C++11)(C++11) Metafunctions conjunction (C++17) disjunction (C++17) negation (C++17)	Supported operations is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11) is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11) is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11) is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11) is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11) is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11) has_virtual_destructor (C++11) is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) Relationships and property queries is_same (C++11) is_convertibleis_nothrow_convertible (C++11)(C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)   is_corresponding_member (C++20) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) is_base_of (C++11) is_virtual_base_of (C++26) alignment_of (C++11) rank (C++11) extent (C++11) is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) Type modifications remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11) remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11) Type transformations aligned_storage (C++11)(deprecated in C++23) aligned_union (C++11)(deprecated in C++23) decay (C++11) remove_cvref (C++20) result_ofinvoke_result (C++11)(until C++20*)(C++17) conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) type_identity (C++20) enable_if (C++11) void_t (C++17)
Compile-time rational arithmetic
Compile-time integer sequences
integer_sequence (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.

Helper variable template

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

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);}

See also

is_array (C++11)	checks if a type is an array type (class template)
extent (C++11)	obtains the size of an array type along a specified dimension (class template)
remove_extent (C++11)	removes one extent from the given array type (class template)
remove_all_extents (C++11)	removes all extents from the given array type (class template)