std::unique_ptr::unique_ptr

From cppreference.com


constexpr unique_ptr();	(1)	(since C++11)

constexpr unique_ptr( nullptr_t );	(1)	(since C++11)

explicit unique_ptr( pointer p );	(2)	(since C++11)

unique_ptr( pointer p, /* see below */ d1 );	(3)	(since C++11)

unique_ptr( pointer p, /* see below */ d2 );	(4)	(since C++11)

unique_ptr( unique_ptr&& u );	(5)	(since C++11)

template< class U, class E > unique_ptr( unique_ptr<U, E>&& u );	(6)	(since C++11)

template< class U > unique_ptr( auto_ptr<U>&& u );	(7)	(since C++11)

1) Constructs an empty std::unique_ptr.

2) Constructs a std::unique_ptr which owns p, initializing the stored pointer with p and value-initializing the stored deleter.

3-4) Constructs a std::unique_ptr object which owns p, initializing the stored pointer with p and initializing a deleter D as below (depends upon whether D is a reference type)

a) If D is non-reference type A, then the signatures are:

unique_ptr(pointer p, const A& d);

unique_ptr(pointer p, A&& d);

b) If D is an lvalue-reference type A&, then the signatures are:

unique_ptr(pointer p, A& d);

unique_ptr(pointer p, A&& d);

c) If D is an lvalue-reference type const A&, then the signatures are:

unique_ptr(pointer p, const A& d);

unique_ptr(pointer p, const A&& d);

5) Constructs a unique_ptr by transferring ownership from u to *this.

6) Constructs a unique_ptr by transferring ownership from u to *this, where u is constructed with a specified deleter (E). It depends upon whether E is a reference type, as following:

a) if E is a reference type, this deleter is copy constructed from u's deleter.

b) if E is a non-reference type, this deleter is move constructed from u's deleter.

7) Constructs a unique_ptr where the stored pointer is initialized with u.release() and the stored deleter is value-initialized.

[edit] Parameters

p	-	a pointer to an object to manage
d1,d2	-	a deleter to use to destroy the object
u	-	another smart pointer to acquire the ownership from

[edit] Exceptions

noexcept specification:


noexcept

(since C++11)

[edit] Example

run this code

#include <iostream>
#include <memory>
 
struct Foo {
    Foo() { std::cout << "Foo...\n"; }
    ~Foo() { std::cout << "~Foo...\n\n"; }
};
 
struct D{
 
    D(){};
 
    D(const D& other){
        std::cout << "call D const copy constructor... \n";
    }
 
    D(D& other){
        std::cout << "call D copy constructor... \n";
    }
 
    D(D&& other){
        std::cout << "call D move constructor... \n";
    }
 
    void operator () (Foo* p) const {
        std::cout << "Call delete for Foo object...\n";
        delete p;
    };
};
 
int main()
{
    //constructor (1)
    std::cout << "Example constructor(1)...\n\n";
    std::unique_ptr<Foo> up;
 
    //constructor (2)
    std::cout << "Example constructor(2)...\n";
    Foo* f = new Foo();
    std::unique_ptr<Foo> up2(f); //up2 now owns f
    up2.reset();
 
    //constructor (3&4)
    std::cout << "Example constructor(3&4)...\n";
 
    //D is not an lvalue-reference - d is a non-const rvalue
    std::unique_ptr<Foo, D> up3(new Foo(), D()); //D must be MoveConstructible
    up3.reset();
 
    //D is not an lvalue-refernce - d is a left value
    D d2;
    std::unique_ptr<Foo, D> up4(new Foo(), d2); //D must be Copyconstructible
    up4.reset();
 
    //D is a left value reference type
    D d3;
    std::unique_ptr<Foo, D&> up5(new Foo(), d3); //up3 holds a reference to d3
    up5.reset();
 
    //D is a const left value reference type
    const D d4;
    std::unique_ptr<Foo, const D&> up6(new Foo(), d4);
    up6.reset();
 
    //constructor (5)
    std::cout << "Example constructor(5)...\n";
    std::unique_ptr<Foo> up7(new Foo());
    std::unique_ptr<Foo> up8(move(up7)); //ownership is transfered to up8
    up8.reset();
 
    //constructor 6
    std::cout << "Example constructor(6)...\n\n";
    std::unique_ptr<Foo> up9(nullptr);
 
    //constructor 7 - D is move constructed
    D d;
    std::cout << "Example constructor(7)...\n";
    std::unique_ptr<Foo, D> up10(new Foo(), d);     //D is not a reference
    std::unique_ptr<Foo, D> up11(move(up10));       //D is move constructed
    up11.reset();
 
    //constructor 7 - D is copy constructed
    std::unique_ptr<Foo, D&> up12(new Foo(), d);    //D is a reference
    std::unique_ptr<Foo, D> up13(move(up12));       //D is copy constructed
    up13.reset();
 
    //constructor 8
    std::cout << "Example constructor(8)...\n";
    std::auto_ptr<Foo> up14(new Foo());
    std::unique_ptr<Foo> up15(move(up14));
    up15.reset();
 
}

Output:

Example constructor(1)...
 
Example constructor(2)...
Foo...
~Foo...
 
Example constructor(3&4)...
Foo...
call D move constructor... 
Call delete for Foo object...
~Foo...
 
Foo...
call D const copy constructor... 
Call delete for Foo object...
~Foo...
 
Foo...
Call delete for Foo object...
~Foo...
 
Foo...
Call delete for Foo object...
~Foo...
 
Example constructor(5)...
Foo...
~Foo...
 
Example constructor(6)...
 
Example constructor(7)...
Foo...
call D const copy constructor... 
call D move constructor... 
Call delete for Foo object...
~Foo...
 
Foo...
call D copy constructor... 
Call delete for Foo object...
~Foo...
 
Example constructor(8)...
Foo...
~Foo...

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