Difference between revisions of "cpp/utility/functional/less"
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Revision as of 17:51, 13 October 2020
| Defined in header <functional>
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| 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.
Contents |
Specializations
Implementation-defined strict total order over pointers
A specialization of std::less for any pointer type yields the implementation-defined strict total order, even if the built-in operator< operator does not.
The implementation-defined strict total order is consistent with the partial order imposed by built-in comparison operators (<=>,(since C++20)<, >, <=, and >=), and consistent among following standard function objects:
- std::less, std::greater, std::less_equal, and std::greater_equal, when the template argument is a pointer type or void(since C++14)
| (since C++20) |
|
The standard library provides a specialization of
|
(since C++14) |
Member types
| Type | Definition |
result_type (deprecated in C++17)(removed in C++20)
|
bool |
first_argument_type (deprecated in C++17)(removed in C++20)
|
T
|
second_argument_type (deprecated in C++17)(removed in C++20)
|
T
|
|
These member types are obtained via publicly inheriting std::binary_function<T, T, bool>. |
(until C++11) |
Member functions
| operator() |
checks whether the first argument is less than the second (public member function) |
std::less::operator()
| 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.
Parameters
| lhs, rhs | - | values to compare |
Return value
true if lhs < rhs, false otherwise.
Exceptions
May throw implementation-defined exceptions.
Possible implementation
constexpr bool operator()(const T &lhs, const T &rhs) const { return lhs < rhs; } |
Example
#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
See also
| function object implementing x > y (class template) |
