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Thread: Smart pointers

  1. #1
    Join Date
    Aug 2002
    Posts
    681

    Smart pointers

    Hi,
    I was told that my code will be greatly simplified if I start using smart pointers available in C++11. However, it is kind of hard for me to get the syntax.

    In the old way I simply write:

    Code:
    std::vector<Foo *> m_myVector;
    m_myVector.push_back( new Foo( <constructor_parameter_list> ) );
    How it will convert using the new syntax?

    Thank you.

  2. #2
    2kaud's Avatar
    2kaud is offline Super Moderator Power Poster
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    Re: Smart pointers

    Code:
    std::vector<unique_ptr<Foo>> m_myVector;
    m_myVector.push_back(make_unique<Foo>(<constructor_parameter_list>));
    For a compilable example consider

    Code:
    	using Foo = int;
    
    	std::vector<std::unique_ptr<Foo>> m_myVector;
    	m_myVector.push_back(make_unique<Foo>(20));
    
    	std::cout << *m_myVector.back() << std::endl;
    you'll also need to include <memory>

    For more info see https://en.cppreference.com/w/cpp/memory

    when m_myvector goes out of scope, all the memory used by the unique_ptr's will be freed automatically.


    Note that a unique_ptr can't be copied - only moved. If you need a smart pointer that can be copied use shared_ptr and make_shared().
    Last edited by 2kaud; June 27th, 2018 at 11:34 AM.
    All advice is offered in good faith only. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!

    C++17 Compiler: Microsoft VS2017 (15.8.7)

  3. #3
    Join Date
    Feb 2017
    Posts
    351

    Re: Smart pointers

    Quote Originally Posted by OneEyeMan View Post
    How it will convert using the new syntax?
    Something like this,

    Code:
    	#include <memory>
    //
    	class Foo {};
    //
    	std::vector<std::shared_ptr<Foo>> m_myVector;
    //
    	m_myVector.push_back(std::make_shared<Foo>(/* <constructor_parameter_list> */));
    The C++ type usually referred to as "smart pointer" is called std::shared_ptr.

    std::make_shared is a convenience function that's often used to create std::shared_ptr<> objects.
    Last edited by wolle; June 27th, 2018 at 11:41 AM.

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