operator==, !=, <, <=, >, >=, <=> (std::shared_ptr)
Defined in header <memory> |
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Compare two shared_ptr objects |
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template < class T, class U > bool operator==( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(1) | (since C++11) |
template< class T, class U > bool operator!=( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(2) | (since C++11) (until C++20) |
template< class T, class U > bool operator<( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(3) | (since C++11) (until C++20) |
template< class T, class U > bool operator>( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(4) | (since C++11) (until C++20) |
template< class T, class U > bool operator<=( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(5) | (since C++11) (until C++20) |
template< class T, class U > bool operator>=( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(6) | (since C++11) (until C++20) |
template< class T, class U > std::strong_ordering operator<=>( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; |
(7) | (since C++20) |
Compare a shared_ptr with a null pointer |
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template< class T > bool operator==( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(8) | (since C++11) |
template< class T > bool operator==( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept; |
(9) | (since C++11) (until C++20) |
template< class T > bool operator!=( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(10) | (since C++11) (until C++20) |
template< class T > bool operator!=( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept; |
(11) | (since C++11) (until C++20) |
template< class T > bool operator<( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(12) | (since C++11) (until C++20) |
template< class T > bool operator<( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept; |
(13) | (since C++11) (until C++20) |
template< class T > bool operator>( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(14) | (since C++11) (until C++20) |
template< class T > bool operator>( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept; |
(15) | (since C++11) (until C++20) |
template< class T > bool operator<=( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(16) | (since C++11) (until C++20) |
template< class T > bool operator<=( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept; |
(17) | (since C++11) (until C++20) |
template< class T > bool operator>=( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(18) | (since C++11) (until C++20) |
template< class T > bool operator>=( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept; |
(19) | (since C++11) (until C++20) |
template< class T > std::strong_ordering operator<=>( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; |
(20) | (since C++20) |
Compares two shared_ptr<T>
objects or compares shared_ptr<T>
with a null pointer.
Note that the comparison operators for shared_ptr
simply compare pointer values; the actual objects pointed to are not compared. Having operator<
defined for shared_ptr
allows shared_ptr
s to be used as keys in associative containers, like std::map
and std::set
.
The |
(since C++20) |
Parameters
lhs | - | the left-hand shared_ptr to compare |
rhs | - | the right-hand shared_ptr to compare |
Return value
lhs.get() == rhs.get()
!(lhs == rhs)
std::less<V>()(lhs.get(), rhs.get())
, where V is the
composite pointer type of
std::shared_ptr<T>::element_type*
and
std::shared_ptr<U>::element_type*
rhs < lhs
!(rhs < lhs)
!(lhs < rhs)
std::compare_three_way{}(x.get(), y.get())
!lhs
!rhs
(bool)lhs
(bool)rhs
std::less<std::shared_ptr<T>::element_type*>()(lhs.get(), nullptr)
std::less<std::shared_ptr<T>::element_type*>()(nullptr, rhs.get())
nullptr < lhs
rhs < nullptr
!(nullptr < lhs)
!(rhs < nullptr)
!(lhs < nullptr)
!(nullptr < rhs)
std::compare_three_way{}(x.get(), static_cast<std::shared_ptr<T>::element_type*>(nullptr))
Notes
In all cases, it is the stored pointer (the one returned by get()
) that is compared, rather than the managed pointer (the one passed to the deleter when use_count
goes to zero). The two pointers may differ in a shared_ptr
created using the aliasing constructor.
Example
#include <iostream> #include <memory> int main() { std::shared_ptr<int> p1(new int(42)); std::shared_ptr<int> p2(new int(42)); std::cout << std::boolalpha << "(p1 == p1) : " << (p1 == p1) << '\n' << "(p1 <=> p1) == 0 : " << ((p1 <=> p1) == 0) << '\n' // Since C++20 // p1 and p2 point to different memory locations, so p1 != p2 << "(p1 == p2) : " << (p1 == p2) << '\n' << "(p1 < p2) : " << (p1 < p2) << '\n' << "(p1 <=> p2) < 0 : " << ((p1 <=> p2) < 0) << '\n' // Since C++20 << "(p1 <=> p2) == 0 : " << ((p1 <=> p2) == 0) << '\n'; // Since C++20 }
Possible output:
(p1 == p1) : true (p1 <=> p1) == 0 : true (p1 == p2) : false (p1 < p2) : true (p1 <=> p2) < 0 : true (p1 <=> p2) == 0 : false
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 3427 | C++20 | operator<=>(shared_ptr, nullptr_t) was ill-formed |
definition fixed |
See also
returns the stored pointer (public member function) |
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