Defined in header <functional> | ||
---|---|---|
template< class T > struct less; | (until C++14) | |
template< class T = void > struct less; | (since C++14) |
Function object for performing comparisons. Unless specialized, invokes operator<
on type T
.
A specialization of std::less
for any pointer type yields a strict total order, even if the built-in operator<
does not. The strict total order is consistent among specializations of std::less
, std::greater
, std::less_equal
, and std::greater_equal
for that pointer type, and is also consistent with the partial order imposed by the corresponding built-in operators (<
, >
, <=
and >=
).
If the function call operator of the specialization | (since C++14) |
The standard library provides a specialization of
| (since C++14) |
Member types
| (until C++20) |
operator() | checks whether the first argument is less than the second (public member function) |
bool operator()( const T& lhs, const T& rhs ) const; | (until C++14) | |
constexpr bool operator()( const T& lhs, const T& rhs ) const; | (since C++14) |
Checks whether lhs
is less than rhs
.
lhs, rhs | - | values to compare |
true
if lhs < rhs
, false
otherwise.
(none).
constexpr bool operator()(const T &lhs, const T &rhs) const { return lhs < rhs; } |
#include <functional> #include <iostream> template <typename A, typename B, typename U = std::less<>> bool f(A a, B b, U u = U()) { return u(a, b); } int main() { std::cout << std::boolalpha; std::cout << f(5, 20) << '\n'; std::cout << f(100, 10) << '\n'; }
Output:
true false
function object implementing x > y (class template) |
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