operator==, !=, <, <=, >, >=, <=> (std::shared_ptr)
Defined in header <memory> |
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Compare two shared_ptr objects. |
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(1) | (since C++11) |
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(2) | (since C++11) (until C++20) |
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(3) | (since C++11) (until C++20) |
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(4) | (since C++11) (until C++20) |
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(5) | (since C++11) (until C++20) |
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(6) | (since C++11) (until C++20) |
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(7) | (since C++20) |
Compare a shared_ptr with a null pointer. |
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(8) | (since C++11) |
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(9) | (since C++11) (until C++20) |
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(10) | (since C++11) (until C++20) |
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(11) | (since C++11) (until C++20) |
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(12) | (since C++11) (until C++20) |
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(13) | (since C++11) (until C++20) |
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(14) | (since C++11) (until C++20) |
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(15) | (since C++11) (until C++20) |
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(16) | (since C++11) (until C++20) |
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(17) | (since C++11) (until C++20) |
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(18) | (since C++11) (until C++20) |
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(19) | (since C++11) (until C++20) |
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(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_ptrs 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
1)
lhs.get() == rhs.get()
2)
!(lhs == rhs)
3)
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*.
4)
rhs < lhs
5)
!(rhs < lhs)
6)
!(lhs < rhs)
7)
std::compare_three_way{}(x.get(), y.get())
8)
!lhs
9)
!rhs
10)
(bool)lhs
11)
(bool)rhs
12)
std::less<std::shared_ptr<T>::element_type*>()(lhs.get(), nullptr)
13)
std::less<std::shared_ptr<T>::element_type*>()(nullptr, rhs.get())
14)
nullptr < lhs
15)
rhs < nullptr
16)
!(nullptr < lhs)
17)
!(rhs < nullptr)
18)
!(lhs < nullptr)
19)
!(nullptr < rhs)
20)
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 : falseDefect 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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