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std::unique_ptr<T,Deleter>::reset

From cppreference.com
< cpp‎ | memory‎ | unique ptr
 
 
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members of the primary template, unique_ptr<T>
void reset( pointer ptr = pointer() ) noexcept;
(1) (constexpr since C++23)
members of the specialization unique_ptr<T[]>
template< class U >
void reset( U ptr ) noexcept;
(2) (constexpr since C++23)
void reset( std::nullptr_t = nullptr ) noexcept;
(3) (constexpr since C++23)

Replaces the managed object.

1,2) Equivalent to auto old_ptr = get();
/* assigns “ptr” to the stored pointer */
if (old_ptr)
    get_deleter()(old_ptr);
.
If get_deleter()(old_ptr) throws an exception, the behavior is undefined.
2) This overload participates in overload resolution only if U is the same type as pointer, or all following conditions are satisfied:
  • pointer is the same type as element_type*.
  • U is a pointer type V* such that V(*)[] is convertible to element_type(*)[].
3) Equivalent to reset(pointer()).

Contents

[edit] Parameters

ptr - pointer to a new object to manage

[edit] 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.

[edit] Example

#include <iostream>
#include <memory>
 
struct Foo // object to manage
{
    Foo() { std::cout << "Foo...\n"; }
    ~Foo() { std::cout << "~Foo...\n"; }
};
 
struct D // deleter
{
    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...

[edit] 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 2118 C++11 unique_ptr<T[]>::reset rejected qualification conversions accepts
LWG 2169 C++11 the overload unique_ptr<T[]>::reset(pointer) existed removed the overload

[edit] See also

returns a pointer to the managed object and releases the ownership
(public member function) [edit]