std::less - cppreference.com (original) (raw)

| Defined in header | | | | ---------------------------------------------------------------------------------- | | ------------- | | template< class T > struct less; | | (until C++14) | | template< class T = void > struct less; | | (since C++14) |

Function object for performing comparisons. The main template invokes operator< on type T.

Contents

• 1 Specializations
• 2 Member types
• 3 Member functions
• 4 std::less::operator()
  • 4.1 Parameters
  • 4.2 Return value
  • 4.3 Exceptions
  • 4.4 Possible implementation
  • 4.5 Example
  • 4.6 Defect reports
  • 4.7 See also

[edit] Specializations

| | function object implementing x < y deducing parameter and return types (class template specialization) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |

[edit] Member types

[edit] Member functions

| | 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; | | (constexpr since C++14) | | ---------------------------------------------------- | | ----------------------- |

Checks whether lhs is less than rhs.

Parameters

Return value

lhs < rhs.

If T is a pointer type, the result is consistent with the implementation-defined strict total order over pointers.

[edit] Exceptions

May throw implementation-defined exceptions.

Possible implementation

constexpr bool operator()(const T& lhs, const T& rhs) const { return lhs < rhs; // assumes that the implementation handles pointer total order }

[edit] Example

#include   template<typename A, typename B, typename C = std::less<>> constexpr bool fun(A a, B b, C cmp = C{}) { return cmp(a, b); }   static_assert(fun(1, 2) == true); static_assert(fun(1.0, 1) == false); static_assert(fun(1, 2.0) == true); static_assert(std::less{}(5, 5.6) == false); // 5 < 5 (warn: implicit conversion) static_assert(std::less{}(5, 5.6) == true); // 5.0 < 5.6 static_assert(std::less{}(5.6, 5.7) == false); // 5 < 5 (warn: implicit conversion) static_assert(std::less{}(5, 5.6) == true); // less: 5.0 < 5.6   int main() {}

[edit] Defect reports

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

[edit] See also