C++: Difference between revisions

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Smart pointers were added in C++11.

There are 3 types of smart pointers:

* ~~<code>unique_ptr<~~/~~code>~~

* [https://en.cppreference.com/w/cpp/memory/unique_ptr <code>unique_ptr</code>] - one piece of code ''owns'' the memory at any given time.

* <code>shared_ptr</~~code>~~

* <code>shared_ptr</code> - the memory has multiple owners.

* <code>weak_ptr</~~code>~~

* <code>weak_ptr</code> - a non-owning reference to a shared_ptr.

~~Use~~ <code>unique_ptr</code> ~~when~~ one piece of code ''owns'' the memory at any given time.

~~Use~~ <code>shared_ptr</code> ~~when~~ multiple ~~objects need to reference the same thing~~.~~ ~~

In general, there should be one object owning an object using a <code>unique_ptr</code>. Whenever you pass the value around, other functions should receive the object as a reference making it clear that they do not have ownership of the object. Smart pointers are nullable and assignable similar to regular pointers.

~~Use~~ <code>weak_ptr</code> to ~~avoid cyclic dependencies which cause issues with reference counting~~.

If you ~~are using C++14 or newer~~, ~~you~~ should use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.

Prefer to use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.

~~Alternatively if you already have a smart pointer, you~~ can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.

You can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.

Example:

@@ Line 265: / Line 265: @@
 Smart pointers were added in C++11.<br>
 There are 3 types of smart pointers:
-* <code>unique_ptr</code>
+* [https://en.cppreference.com/w/cpp/memory/unique_ptr <code>unique_ptr</code>] - one piece of code ''owns'' the memory at any given time.<br>
-* <code>shared_ptr</code>
+* <code>shared_ptr</code> - the memory has multiple owners.
-* <code>weak_ptr</code>
+* <code>weak_ptr</code> - a non-owning reference to a shared_ptr.
-Use <code>unique_ptr</code> when one piece of code ''owns'' the memory at any given time.<br>
-Use <code>shared_ptr</code> when multiple objects need to reference the same thing.<br>
+In general, there should be one object owning an object using a <code>unique_ptr</code>. Whenever you pass the value around, other functions should receive the object as a reference making it clear that they do not have ownership of the object. Smart pointers are nullable and assignable similar to regular pointers.
-Use <code>weak_ptr</code> to avoid cyclic dependencies which cause issues with reference counting.<br>
-If you are using C++14 or newer, you should use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.<br>
+Prefer to use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.<br>
-Alternatively if you already have a smart pointer, you can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.
+You can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.
 Example:
 <syntaxhighlight lang="cpp">