std::unique_ptr::unique_ptr

default constructor (1), and (2)

The object is empty (owns nothing), with value-initialized stored pointer and stored deleter.

construct from pointer (3)

The object takes ownership of p, initializing its stored pointer to p and value-initializing its stored deleter.

construct from pointer + lvalue deleter (4)

The object takes ownership of p, initializing its stored pointer to p, and using a copy of d as deleter (unless D is a reference type, in which case, d is used directly).

construct from pointer + rvalue deleter (5)

The object takes ownership of p, initializing its stored pointer to p and moving d into the object to be used as deleter.

move constructors (6) and (7)

The object acquires the content managed by x, moving into the object both its stored pointer (of which it takes ownership) and its stored deleter (unless x's deleter type is a reference, in which case the deleter is copied instead of moved).

construct by moving auto_ptr (8)

The object acquires the content managed by x, initializing its stored pointer as if by calling x.release() (taking ownership of the pointer), and value-initializing its stored deleter.

copy construction (9)

Copy construction is disabled for objects of type unique_ptr (see move constructors, 6 and 7).

Parameters

p

Pointer whose ownership is taken over by the object.
This pointer value shall not be already managed by any other managed pointer (i.e., this value shall not come from calling member get on a managed pointer).
pointer is a member type, defined as the pointer type that points to the type of object managed.

del

Deleter object to be used to release the owned object.
D refers to unique_ptr's second template parameter, which describes its deleter type.

x

A unique_ptr or auto_ptr object.
U* shall be implicitly convertible to T* (where T is unique_ptr's first template parameter).

Example

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// unique_ptr constructor example
#include <iostream>
#include <memory>
int main () {
  std::default_delete<int> d;
  std::unique_ptr<int> u1;
  std::unique_ptr<int> u2 (nullptr);
  std::unique_ptr<int> u3 (new int);
  std::unique_ptr<int> u4 (new int, d);
  std::unique_ptr<int> u5 (new int, std::default_delete<int>());
  std::unique_ptr<int> u6 (std::move(u5));
  std::unique_ptr<int> u7 (std::move(u6));
  std::unique_ptr<int> u8 (std::auto_ptr<int>(new int));
  std::cout << "u1: " << (u1?"not null":"null") << '\n';
  std::cout << "u2: " << (u2?"not null":"null") << '\n';
  std::cout << "u3: " << (u3?"not null":"null") << '\n';
  std::cout << "u4: " << (u4?"not null":"null") << '\n';
  std::cout << "u5: " << (u5?"not null":"null") << '\n';
  std::cout << "u6: " << (u6?"not null":"null") << '\n';
  std::cout << "u7: " << (u7?"not null":"null") << '\n';
  std::cout << "u8: " << (u8?"not null":"null") << '\n';
  return 0;
}

u1: null
u2: null
u3: not null
u4: not null
u5: null
u6: null
u7: not null
u8: not null

See also

unique_ptr::operator=

unique_ptr assignment (public member function)

unique_ptr::reset

Reset pointer (public member function)

unique_ptr::~unique_ptr

Destroy unique_ptr (public member function)