std::swap(std::weak_ptr)
Since C++11
template< class T >
void swap( std::weak_ptr<T>& lhs, std::weak_ptr<T>& rhs ) noexcept;
Specializes the std::swap
algorithm for std::weak_ptr
. Swaps the contents of lhs
and rhs
. Calls lhs.swap(rhs)
.
Parameters
lhs
, rhs
- smart pointers whose contents to swap
Return value
(none)
Complexity
Constant
Example
#include <iostream>
#include <memory>
#include <string>
struct Foo {
Foo(int _val) : val(_val) { std::cout << "Foo...\n"; }
~Foo() { std::cout << "~Foo...\n"; }
std::string print() { return std::to_string(val); }
int val;
};
int main()
{
std::shared_ptr<Foo> sp1 = std::make_shared<Foo>(100);
std::shared_ptr<Foo> sp2 = std::make_shared<Foo>(200);
std::weak_ptr<Foo> wp1 = sp1;
std::weak_ptr<Foo> wp2 = sp2;
auto print = [&]() {
auto p1 = wp1.lock();
auto p2 = wp2.lock();
std::cout
<< " p1=" << (p1 ? p1->print() : "nullptr");
std::cout
<< " p2=" << (p2 ? p2->print() : "nullptr")
<< '\n';
};
print();
std::swap(wp1, wp2);
print();
wp1.reset();
print();
std::swap(wp1, wp2);
print();
}
Result
Foo...
Foo...
p1=100 p2=200
p1=200 p2=100
p1=nullptr p2=100
p1=100 p2=nullptr
~Foo...
~Foo...