Defined in header <functional>  

template< class T > struct less_equal;  (until C++14)  
template< class T = void > struct less_equal;  (since C++14) 
Function object for performing comparisons. Unless specialized, invokes operator<=
on type T
.
A specialization of std::less_equal
for any pointer type yields the implementationdefined strict total order, even if the builtin <=
operator does not.
The implementationdefined strict total order is consistent with the partial order imposed by builtin 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) 
(C++14)  function object implementing x <= y deducing argument and return types (class template specialization) 
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  (until C++11) 
operator()  checks if the first argument is less than or equal to 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 if lhs
is less than or equal to rhs
.
lhs, rhs    values to compare 
For T
which is not a pointer type, true
if lhs <= rhs
, false
otherwise.
For T
which is a pointer type, true
if lhs
does not succeed rhs
in the implementationdefined strict total order, false
otherwise.
May throw implementationdefined exceptions.
constexpr bool operator()(const T &lhs, const T &rhs) const { return lhs <= rhs; // assumes that the implementation uses a flat address space } 
function object implementing x < y (class template) 

(C++20)  function object implementing x <= y (class) 
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