std::unique_ptr::reset
From cppreference.com
< cpp | memory | unique ptr
| members of the primary template, unique_ptr<T> |
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| void reset( pointer ptr = pointer() ) noexcept; |
(1) | |
| members of the specialization unique_ptr<T[]> |
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| void reset( pointer ptr = pointer() ) noexcept; |
(2) | (until C++17) |
| (3) | ||
| template< class U > void reset( U ) = delete; |
(until C++17) | |
| template< class U > void reset( U ) noexcept; |
(since C++17) | |
| (4) | ||
| void reset( std::nullptr_t p ) noexcept; |
(until C++17) | |
| void reset( std::nullptr_t p = nullptr ) noexcept; |
(since C++17) | |
Replaces the managed object.
1) Given
current_ptr, the pointer that was managed by *this, performs the following actions, in this order:
- Saves a copy of the current pointer old_ptr = current_ptr
- Overwrites the current pointer with the argument current_ptr = ptr
- If the old pointer was non-empty, deletes the previously managed object if(old_ptr) get_deleter()(old_ptr).
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2) Behaves the same as the reset member of the primary template.
3) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this template member is provided to prevent using reset() with a pointer to derived (which would result in undefined behavior with arrays).
4) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this overload is necessary to allow reset to nullptr (which would otherwise be prohibited by the template overload). Equivalent to reset(pointer())
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(until C++17) |
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3) Behaves the same as the reset member of the primary template, except that it will only participate in overload resolution if either
4) Equivalent to reset(pointer())
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(since C++17) |
Parameters
| ptr | - | pointer to a new object to manage |
Return value
(none)
Notes
To replace the managed object while supplying a new deleter as well, move assignment operator may be used.
A test for self-reset, i.e. whether ptr points to an object already managed by *this, is not performed, except where provided as a compiler extension or as a debugging assert. Note that code such as p.reset(p.release()) does not involve self-reset, only code like p.reset(p.get()) does.
Example
Run this code
#include <iostream> #include <memory> struct Foo { Foo() { std::cout << "Foo...\n"; } ~Foo() { std::cout << "~Foo...\n"; } }; struct D { void operator() (Foo* p) { std::cout << "Calling delete for Foo object... \n"; delete p; } }; int main() { std::cout << "Creating new Foo...\n"; std::unique_ptr<Foo, D> up(new Foo(), D()); // up owns the Foo pointer (deleter D) std::cout << "Replace owned Foo with a new Foo...\n"; up.reset(new Foo()); // calls deleter for the old one std::cout << "Release and delete the owned Foo...\n"; up.reset(nullptr); }
Output:
Creating new Foo... Foo... Replace owned Foo with a new Foo... Foo... Calling delete for Foo object... ~Foo... Release and delete the owned Foo... Calling delete for Foo object... ~Foo...
See also
| returns a pointer to the managed object and releases the ownership (public member function) |