std::shared_ptr Exception Safety

c++, c++11, memory-leaks, shared-ptr

Solution

template<class Y> explicit shared_ptr(Y* p);

[util.smartptr.shared.const]/6 Throws: `bad_alloc`, or an implementation-defined exception when a resource other than memory could not be obtained. [util.smartptr.shared.const]/7 Exception safety: If an exception is thrown, `delete p` is called.

So no, no memory leak.

Problem

I just realised reading this page that the constructor of `std::shared_ptr` with a single pointer argument is not noexcept. Hence the following code contains a possible memory leak: ``` std::shared_ptr<int> p3 (new int); ``` The reasonning is that two allocations could occure: - The first one before the call to the constructor - The second one in the constructor of shared_ptr (This is what happens in VS 2012 for example) Two questions here: Is it true that if the second allocation throws an exception, the memory of the first one leaks ? If the answer is yes: what is the correct idiom to use std::shared_ptr? - using make_shared - giving the ownership of the first allocation to a std::unique_ptr then transfering the ownership - Other thoughts ?

Original source