std::less
| 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.
Specializations
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 >=).
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If the function call operator of the specialization |
(since C++14) |
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The standard library provides a specialization of
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(since C++14) |
Member types
| type | definition |
result_type(deprecated in C++17)
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bool
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first_argument_type(deprecated in C++17)
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T
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second_argument_type(deprecated in C++17)
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T
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Member functions
| operator() |
checks if 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
(none)
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<int>> 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
| (C++11) |
provides mixed-type owner-based ordering of shared and weak pointers (class template) |
| function object implementing x > y (class template) |