CODEWITHSUNDEEP
c++unique-ptr
user3828398
user3828398

Reputation: 565

c++ how to convert already created object to unique_ptr

I have a get function which returns an object of type MyClass called myObject:

MyClass myObject = something.get(id);

I want to convert myObject to unique_ptr, how to do it?

std::unique_ptr<MyClass>(&myObject); // Is this correct?

Upvotes: 18

Views: 32040

Answers (2)

Zafi
Zafi

Reputation: 629

If you would initialize it with the reference, it would give problems when you get out of scope. One possibility:

// Example program
#include <iostream>
#include <string>
#include <memory>

struct MyClass
{
};

int main()
{
   MyClass myObject;
   std::unique_ptr<MyClass>( new MyClass(myObject) ); 
}

Upvotes: 0

george_ptr
george_ptr

Reputation: 598

MyClass myObject = something.get(id);

Implies either copy or move construction.

If your copy constructor is defined and declared public try the following

std::unique_ptr<MyClass> my_p_obj( new MyClass(myObject) );

Where you create a new object and initialize it by copying.

Otherwise the object in your example is initialized through move construction

std::unique_ptr<MyClass> my_p_obj( new MyClass( std::move(myObject) ) );

what's wrong with std::unique_ptr(&myObject);

myObject is an object in the local scope which will be destroyed when the function it lies in reaches the end (}). If you call the destructor twice (one from the compiler, the second from unique_ptr) you get undefined behaviour

Edit : As cleared up in the comments, you could make use of auto my_p_obj = std::make_unique<MyClass>(myObject) which does the same thing. – Thanks, Andreas H.

Upvotes: 20

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