From cppreference.com
Defined in header
template<classT>structnegate;(until C++14)template<classT=void>structnegate;(since C++14)Function object for performing negation. Effectively calls operator- on an instance of type T.
Specializations
The standard library provides a specialization of std::negate when T is not specified, which leaves the parameter types and return type to be deduced.
(C++14)
function object implementing -x deducing parameter and return types
(class template specialization)
(since C++14)Member types
Type Definition result_type(deprecated in C++17)(removed in C++20)Targument_type(deprecated in C++17)(removed in C++20)TThese member types are obtained via publicly inheriting std::unary_function<T,T>.
(until C++11)Member functions
operator()
returns the negation of the argument
(public member function)std::negate::operator()
Toperator()(constT&arg)const;(constexpr since C++14)Returns the negation of arg.
Parameters
arg - value to compute negation of Return value
The result of -arg.
Exceptions
May throw implementation-defined exceptions.
Possible implementation
constexprToperator()(constT&arg)const{return-arg;}