std::cmp_equal, cmp_not_equal, cmp_less, cmp_greater, cmp_less_equal, cmp_greater_equal

 

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)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20)   bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17) to_chars_result (C++17) from_chars_result (C++17)

 

Defined in header <utility>
template< class T, class U > constexpr bool cmp_equal( T t, U u ) noexcept;	(1)	(since C++20)
template< class T, class U > constexpr bool cmp_not_equal( T t, U u ) noexcept;	(2)	(since C++20)
template< class T, class U > constexpr bool cmp_less( T t, U u ) noexcept;	(3)	(since C++20)
template< class T, class U > constexpr bool cmp_greater( T t, U u ) noexcept;	(4)	(since C++20)
template< class T, class U > constexpr bool cmp_less_equal( T t, U u ) noexcept;	(5)	(since C++20)
template< class T, class U > constexpr bool cmp_greater_equal( T t, U u ) noexcept;	(6)	(since C++20)

Compare the values of two integers t and u. Unlike builtin comparison operators, negative signed integers always compare less than (and not equal to) unsigned integers: the comparison is safe against non-value-preserving integer conversion.

-1 > 0u; // true
std::cmp_greater(-1, 0u); // false

It is a compile-time error if either T or U is a non-integer type, a character type, or bool.

Parameters

t	-	left-hand argument
u	-	right-hand argument

Return value

1) true if t is equal to u.

2) true if t is not equal to u.

3) true if t is less than u.

4) true if t is greater than u.

5) true if t is less or equal to u.

6) true if t is greater or equal to u.

Possible implementation

template<class T, class U> constexpr bool cmp_equal(T t, U u) noexcept { if constexpr (std::is_signed_v<T> == std::is_signed_v<U>) return t == u; else if constexpr (std::is_signed_v<T>) return t >= 0 && std::make_unsigned_t<T>(t) == u; else return u >= 0 && std::make_unsigned_t<U>(u) == t; }   template<class T, class U> constexpr bool cmp_not_equal(T t, U u) noexcept { return !cmp_equal(t, u); }   template<class T, class U> constexpr bool cmp_less(T t, U u) noexcept { if constexpr (std::is_signed_v<T> == std::is_signed_v<U>) return t < u; else if constexpr (std::is_signed_v<T>) return t < 0 || std::make_unsigned_t<T>(t) < u; else return u >= 0 && t < std::make_unsigned_t<U>(u); }   template<class T, class U> constexpr bool cmp_greater(T t, U u) noexcept { return cmp_less(u, t); }   template<class T, class U> constexpr bool cmp_less_equal(T t, U u) noexcept { return !cmp_less(u, t); }   template<class T, class U> constexpr bool cmp_greater_equal(T t, U u) noexcept { return !cmp_less(t, u); }

Notes

These functions cannot be used to compare enums (including std::byte), char, char8_t, char16_t, char32_t, wchar_t and bool.

Feature-test macro	Value	Std	Feature
__cpp_lib_integer_comparison_functions	202002L	(C++20)	Integer comparison functions

Example

The example below might produce different signedness comparison warning if compiled without an appropriate warning suppression flag, e.g., -Wno-sign-compare (gcc/clang with -Wall -Wextra, see also SO: disabling a specific warning).

Run this code

#include <utility>
 
// Uncommenting the next line will disable "signed/unsigned comparison" warnings:
// #pragma GCC diagnostic ignored "-Wsign-compare"
 
int main()
{
    static_assert(sizeof(int) == 4); // precondition
 
    // Quite surprisingly
    static_assert(-1 > 1U); //< warning: sign-unsign comparison
    // because after implicit conversion of -1 to the RHS type (`unsigned int`)
    // the expression is equivalent to:
    static_assert(0xFFFFFFFFU > 1U);
    static_assert(0xFFFFFFFFU == static_cast<unsigned>(-1));
 
    // In contrast, the cmp_* family compares integers as most expected -
    // negative signed integers always compare less than unsigned integers:
    static_assert(std::cmp_less(-1, 1U));
    static_assert(std::cmp_less_equal(-1, 1U));
    static_assert(!std::cmp_greater(-1, 1U));
    static_assert(!std::cmp_greater_equal(-1, 1U));
 
    static_assert(-1 == 0xFFFFFFFFU); //< warning: sign-unsign comparison
    static_assert(std::cmp_not_equal(-1, 0xFFFFFFFFU));
}

See also

equal_to	function object implementing x == y (class template)
not_equal_to	function object implementing x != y (class template)
less	function object implementing x < y (class template)
greater	function object implementing x > y (class template)
less_equal	function object implementing x <= y (class template)
greater_equal	function object implementing x >= y (class template)
ranges::equal_to (C++20)	constrained function object implementing x == y (class)
ranges::not_equal_to (C++20)	constrained function object implementing x != y (class)
ranges::less (C++20)	constrained function object implementing x < y (class)
ranges::greater (C++20)	constrained function object implementing x > y (class)
ranges::less_equal (C++20)	constrained function object implementing x <= y (class)
ranges::greater_equal (C++20)	constrained function object implementing x >= y (class)
compare_three_way (C++20)	constrained function object implementing x <=> y (class)
in_range (C++20)	checks if an integer value is in the range of a given integer type (function template)
numeric_limits	provides an interface to query properties of all fundamental numeric types (class template)