CODEWITHSUNDEEP
c++vectorinitializationshared-ptr
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Reputation: 720

Vector construction when wrapped in a Shared Pointer

So I am working on a transformation from an OO-language with garbage collection capabilities to C++. To start out I want to wrap all objects in shared pointers to solve the memory de-allocation issue. Right now I am trying to wrap a vector in a shared pointer and initializing the vector directly. See the issue below. Why is it not working and, if possible, how do I make it work?

vector<int> vec({ 6, 4, 9 }); // Working

shared_ptr<vector<int>> vec = make_shared<vector<int>>({ 6, 4, 9 }); // Not working

Sorry for not including the error, the error I am getting is marked at (make_shared) and printed as:

no instance of function template "std::make_shared" matches the argument list
argument types are: ({...})

Thanks for any answers!

Upvotes: 12

Views: 9177

Answers (4)

Drax
Drax

Reputation: 13288

Brace initializer list cannnot be used in most type deduction contexts.

If you explicitly specify the type it works:

std::shared_ptr<std::vector<int>> vec = std::make_shared<std::vector<int>>(std::vector<int>{ 6, 4, 9 });

Upvotes: 13

Chris Drew
Chris Drew

Reputation: 15334

make_shared does not support non-explicit initializer lists. You could make use of the fact that auto can deduce an initializer list:

auto init = { 6, 4, 9 };
auto vec = std::make_shared<std::vector<int>>(init);

But as others have pointed out, you need to consider if you need a shared_ptr at all, vector manages its own memory. shared_ptr is not free.

Upvotes: 0

nh_
nh_

Reputation: 2241

auto vec = make_shared<vector<int>>(std::initializer_list<int>{ 6, 4, 9 });

Upvotes: 3

John Zwinck
John Zwinck

Reputation: 249153

Initializer lists don't play well with make_shared. For more detail, see here: std::make_shared with std::initializer_list

But probably the real solution is to not hold your vector in a smart pointer at all--not everything deserves a smart pointer anyway. But if you want to stick with it, this should work:

shared_ptr<vector<int>> vec(new vector<int>({ 6, 4, 9 }));

Upvotes: 0

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