Questions tagged [rule-of-three]

The rule of three (also known as the Law of The Big Three or The Big Three) is a rule of thumb in C++ that claims that if a class defines one of the following it should probably explicitly define all three: destructor, copy constructor, assignment operator

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What is The Rule of Three?

What does copying an object mean? What are the copy constructor and the copy assignment operator? When do I need to declare them myself? How can I prevent my objects from being copied?
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Rule-of-Three becomes Rule-of-Five with C++11?

So, after watching this wonderful lecture on rvalue references, I thought that every class would benefit of such a "move constructor", template MyClass(T&& other) edit and of course a "move assignment operator", template MyClass&…
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Must a c++ interface obey the rule of five?

What is the correct way to declare instantiation methods when defining an interface class? Abstract base classes are required to have a virtual destructor for obvious reasons. However, the following compilation warning is then given:…
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Understanding -Weffc++

Consider the following program: #include struct S { S (){} private: void *ptr = nullptr; std::string str = ""; }; int main(){} This, when compiled with -Weffc++ on GCC 4.7.1, will spit out: warning: 'struct S' has pointer…
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Exception to the Rule of Three?

I've read a lot about the C++ Rule of Three. Many people swear by it. But when the rule is stated, it almost always includes a word like "usually," "likely," or "probably," indicating that there are exceptions. I haven't seen much discussion of what…
Sam Kauffman
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Is CppCoreGuidelines C.21 correct?

While reading the Bjarne Stroustrup's CoreCppGuidelines, I have found a guideline which contradicts my experience. The C.21 requires the following: If you define or =delete any default operation, define or =delete them all With the following…
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C++ Copy Constructor + Pointer Object

I'm trying to learn "big three" in C++.. I managed to do very simple program for "big three".. but I'm not sure how to use the object pointer.. The following is my first attempt. I have a doubt when I was writing this... Questions Is this the…
Michael Sync
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Safe assignment and copy-and-swap idiom

I'm learning c++ and I recently learned (here in stack overflow) about the copy-and-swap idiom and I have a few questions about it. So, suppose I have the following class using a copy-and-swap idiom, just for example: class Foo { private: int *…
Rafael S. Calsaverini
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rule of five and implicitly deleted functions

For my understanding, the rule of five is a guidelince rule. Altough, I've seen that the compiler in some scenarios may delete functions, implicitly. For example, when defining a move-ctor', the copy assignment/ copy ctor' will be deleted. I'd like…
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What's with the copy-constructor if the class contains a user-declared destructor?

The Standard in section 12.8/7 says: If the class definition does not explicitly declare a copy constructor, one is declared implicitly. If the class definition declares a move constructor or move assignment operator, the implicitly declared…
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Storing objects in STL vector - minimal set of methods

What is "minimal framework" (necessary methods) of complex object (with explicitly malloced internal data), which I want to store in STL container, e.g. ? For my assumptions (example of complex object Doit): #include #include…
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Rule of 3 Default Member Deprecation in C++11

According to the below widely-known table, automatic compiler generation of default copy constructor and copy assignment is deprecated in C++11 when one or more of the copy assignment, copy constructor, and destructor is/are supplied by the user…
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Do C++ abstract classes need to obey the rule of five?

When implementing an abstract class like this: class Base { public: virtual ~Base() = default; virtual void foo() = 0; }; Does this interface have to obey the rule of five i.e. do I have to add a copy constructor, copy assignment operator,…
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When assigning in C++, does the object we assigned over get destructed?

Does the following code fragment leak? If not, where do the two objects which are constructed in foobar() get destructed? class B { int* mpI; public: B() { mpI = new int; } ~B() { delete mpI; } }; void foobar() { B b; b = B(); //…
Tony Park
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Am I violating Rule of three?

I recently read, Rule of three and am wondering if I am violating it? In my GUI application, classes like MainFrame, Interface, Circuit, Breadboard etc. (class name are indicative) have a single instance of each of them. In their constructors, I…
Vinayak Garg
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