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std::swap(std::unique_ptr)

Defined in header <memory>.

Declarations

C++11
template< class T, class D >
void swap( std::unique_ptr<T, D>& lhs, std::unique_ptr<T, D>& rhs ) noexcept;
C++23
template< class T, class D >
constexpr void swap( std::unique_ptr<T, D>& lhs, std::unique_ptr<T, D>& rhs ) noexcept;

Specializes the std::swap algorithm for std::unique_ptr. Swaps the contents of lhs and rhs. Calls lhs.swap(rhs).

This function does not participate in overload resolution unless std::is_swappable_v<D> is true(since C++17).

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::unique_ptr<Foo> p1 = std::make_unique<Foo>(100);
std::unique_ptr<Foo> p2 = std::make_unique<Foo>(200);
auto print = [&]() {
std::cout
<< " p1="
<< (p1 ? p1->print() : "nullptr");
std::cout
<< " p2="
<< (p2 ? p2->print() : "nullptr")
<< '\n';
};
print();

std::swap(p1, p2);
print();

p1.reset();
print();

std::swap(p1, p2);
print();
}
Result
Foo...
Foo...
p1=100 p2=200
p1=200 p2=100
~Foo...
p1=nullptr p2=100
p1=100 p2=nullptr
~Foo...

std::swap(std::unique_ptr)

Defined in header <memory>.

Declarations

C++11
template< class T, class D >
void swap( std::unique_ptr<T, D>& lhs, std::unique_ptr<T, D>& rhs ) noexcept;
C++23
template< class T, class D >
constexpr void swap( std::unique_ptr<T, D>& lhs, std::unique_ptr<T, D>& rhs ) noexcept;

Specializes the std::swap algorithm for std::unique_ptr. Swaps the contents of lhs and rhs. Calls lhs.swap(rhs).

This function does not participate in overload resolution unless std::is_swappable_v<D> is true(since C++17).

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::unique_ptr<Foo> p1 = std::make_unique<Foo>(100);
std::unique_ptr<Foo> p2 = std::make_unique<Foo>(200);
auto print = [&]() {
std::cout
<< " p1="
<< (p1 ? p1->print() : "nullptr");
std::cout
<< " p2="
<< (p2 ? p2->print() : "nullptr")
<< '\n';
};
print();

std::swap(p1, p2);
print();

p1.reset();
print();

std::swap(p1, p2);
print();
}
Result
Foo...
Foo...
p1=100 p2=200
p1=200 p2=100
~Foo...
p1=nullptr p2=100
p1=100 p2=nullptr
~Foo...