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

 

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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 lossy integer conversion.

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

It is a compile-time error if either T or U is not a signed or unsigned integer type (including standard integer type and extended integer type).

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 { using UT = std::make_unsigned_t<T>; using UU = std::make_unsigned_t<U>; 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 ? false : UT(t) == u; else return u < 0 ? false : t == UU(u); }   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 { using UT = std::make_unsigned_t<T>; using UU = std::make_unsigned_t<U>; 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 ? true : UT(t) < u; else return u < 0 ? false : t < UU(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_greater(t, u); }   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.

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)