std::ranges::less

 

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Operator wrappers plus minus negate multiplies divides modulus bit_and bit_or bit_not (C++14)   bit_xor equal_to not_equal_to greater less greater_equal less_equal logical_and logical_or logical_not	Transparent operator wrappers plus<> (C++14) minus<> (C++14) negate<> (C++14) multiplies<> (C++14)   divides<> (C++14) modulus<> (C++14) bit_and<> (C++14) bit_or<> (C++14) bit_not<> (C++14) bit_xor<> (C++14) equal_to<> (C++14) not_equal_to<> (C++14) greater<> (C++14) less<> (C++14) greater_equal<> (C++14) less_equal<> (C++14) logical_and<> (C++14) logical_or<> (C++14) logical_not<> (C++14)
Negators not_fn (C++17) Searchers default_searcher (C++17) boyer_moore_searcher (C++17) boyer_moore_horspool_searcher (C++17)	Constrained comparators ranges::equal_to (C++20) ranges::not_equal_to (C++20) ranges::greater (C++20) ranges::less (C++20) ranges::greater_equal (C++20) ranges::less_equal (C++20) compare_three_way (C++20)
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unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

Defined in header <functional>
struct less;		(since C++20)

Function object for performing comparisons. Deduces the parameter types of the function call operator from the arguments (but not the return type).

Nested types

Nested type	Definition
is_transparent	unspecified

Member functions

operator()

checks if the first argument is less than the second (public member function)

std::ranges::less::operator()

template< class T, class U > constexpr bool operator()( T&& t, U&& u ) const;

Given the expression std::forward<T>(t) < std::forward<U>(u) as expr:

• If expr results in a call to built-in operator< comparing pointers, given the composite pointer type of t and u as P:

• If the converted t precedes the converted u (both are of type P) in the implementation-defined strict total order over pointers, returns true, otherwise returns false.
• If the conversion sequence from T to P or the conversion sequence from U to P is not equality-preserving, the behavior is undefined.

• Otherwise:

• Returns the result of expr.
• If std::totally_ordered_with<T, U> is not modeled, the behavior is undefined.

This overload participates in overload resolution only if std::totally_ordered_with<T, U> is satisfied.

If there exists an expression expr1 of type T and an expression expr2 of U, such that the comparison results of expr1 and expr2 violate strict total ordering (rules are defined below), the behavior is undefined.

The comparison results of expr1 and expr2 follow strict total ordering only if exactly one of the following expressions is true:

• std::ranges::less{}(expr1, expr2)
• std::ranges::less{}(expr2, expr1)
• std::ranges::equal_to{}(expr1, expr2)

Notes

Unlike std::less, std::ranges::less requires all six comparison operators <, <=, >, >=, == and != to be valid (via the totally_ordered_with constraint).

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3530	C++20	syntactic checks were relaxed while comparing pointers	only semantic requirements are relaxed

See also

less	function object implementing x < y (class template)