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Posted 15 Mar 2019
Licenced MIT

Refactoring std::auto_ptr

, 15 Mar 2019
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How to refactor std::auto_ptr

A colleague at work was recently tasked with refactoring some legacy code and came across the good old std::auto_ptr. In C++0x, it has been deprecated (and later removed outright; I can’t even compile std::auto_ptr code in Visual Studio 2017 nor Xcode 10.1) so it was his job to rewrite it in the modern C++ way. The code that my colleague came across had another problem. Can you spot it?

std::auto_ptr<T> p1(new T[3]);

std::auto_ptr was never meant to hold pointers to arrays. So the code above, assuming it didn’t crash, was leaking memory (regardless of what it holds, std::auto_ptr always calls delete in its destructor; delete[] was needed in the code above).

So how do we refactor legacy std::auto_ptr code into modern C++? The answer is std::unique_ptr ( A std::auto_ptr holding a pointer to a single object of type T, in modern C++, becomes:

auto p2 = std::make_unique<T>();

std::make_unique can forward constructor parameters to T::T, like this:

auto p3 = std::make_unique<T>("string parameter");

And an array of Ts of size N becomes:

auto p4 = std::make_unique<T[]>(N);

Note that for std::make_unique to be able to create an array of Ts, T must have a T::T() (default constructor; or a constructor with all parameters having default values: T::T(int x = 0)).


This article, along with any associated source code and files, is licensed under The MIT License


About the Author

Martin Vorbrodt
Software Developer (Senior)
United States United States
No Biography provided

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Comments and Discussions

Suggestionshared_ptr Pin
Stefan_Lang20-Mar-19 22:27
memberStefan_Lang20-Mar-19 22:27 
Questionmake_unique Pin
Stefan_Lang20-Mar-19 22:26
memberStefan_Lang20-Mar-19 22:26 

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