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internal data structures and copies all data from the other object to self */ deep_copy(const deep_copy& dc) { if (dynamic_data == NULL) dynamic_data = new int; if (this != &dc) *dynamic_data =* (dc.dynamic_data); } /* Overloaded assigment operator which copies all data from the other object to self */ deep_copy& operator=(const deep_copy& dc) { if (this != &dc) *dynamic_data = *(dc.dynamic_data); return *this; } /* Destructor which delete all dynamic allocated data */ ~deep_copy() { delete(dynamic_data); } /* Prints data inside object - only for demonstration of functionality */ void vypis() { cout << *dynamic_data; } }; int main(int argc, char *argv) { deep_copy *x = new deep_copy(3); // I create new dynamic number deep_copy *y = new deep_copy(0); // I create new dynamic number *y = *x; // I make a deep copy, so y = 3 *x = 4; // Using a copy constructor i set x to 4 x-: -->
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subobject is of class type, the copy constructor for the class is used; — if the subobject is an array, each element is copied, in the manner appropriate to the element type; — if the subobject is of scalar type, the built-in assignment operator is used. Virtual base class subobjects shall be copied only once by the implicitly-defined copy constructor (see 12.6.2).
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it's unsafe to call setDesignation with a string longer than the string used to construct the
Employee instance. The default constructor does nothing to initialize the designation string either. Finally, the whole example is very unsafe and promotes incorrect C++ programming. I suggest it be replaced with a more effective example.
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The implicitly-defined copy constructor for class X performs a memberwise copy of its subobjects. The order of copying is the same as the order of initialization of bases and members in a user-defined constructor (see 12.6.2). Each subobject is copied in the manner appropriate to its type: — if the
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Note that it is a purely aesthetic change, however there was mixed usage throughout the article, so this change might reduce any confusion for those new to the language. In addition, although it violates the easy-to-read nature of right-to-left declarations, it is the far more common form, though I
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Deep copy is a way how the data inside the objects are copied during invocation of copy constructor or assignment operator. The essence of deep copy is that it copies all data inside the object (not only pointers on the data). Other ways doesn't copy dynamic alocated data, they create a bit copy of
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I added a definition for the copy constructor as it is defined in the C++ standard. There is a bug in the example program that was provided for the explicit copy constructor. First, it is not allocating the correct length of characters: it should be strlen(dsgn) + 1. It's missing the "+ 1". Also,
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using namespace std; class deep_copy { int *dynamic_data; public: /* Constructor initializes internal data structures */ deep_copy(int data) { dynamic_data = new int; *dynamic_data = data; } /* Copy constructor initializes
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An object is returned by a function. C++ calls a copy constructor to make a copy of an object in each of the above cases. If there is no copy constructor defined for the class, C++ uses the default copy constructor which copies each field, ie, makes a shallow copy.
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I think, it will be great if someone with good c++ skills will modify Copy constructors and templates section, and write more about "An explicit, non-template, copy constructor must also be provided for construction of Array from Array." with
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it is mentioned that the compiler will create a temporary object, then invoke the copy constructor X::X(const X&) Not sure what the standard says, but with Visual Studio, the copy constructor is not invoked in the following example:
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I read in this article : "Hence, there is always one copy constructor that is either defined by the user or by the system." However, it seems to me that one can remove such a copy constructor in C++11 such as in the following example :
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am too lazy to prove that. It is, however, the order that the standard uses so it is probably best to talk about qualifier order else-where, and focus on the copy constructors themselves here. To clarify the change I made is here:
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Yes, I agree. A better example should be written for this article. Why does the above example allocate a deep_copy in the free store? It is an unnecessary (and misleading) complication that contributes nothing to this article.
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This article has an error regarding the implicit copy constructor. It does not perform a "byte-by-byte" copy of its members, since its members could have user-defined copy constructors as well. The standard (2003, 12</math:
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first object, so the copied pointers inside the new object still refers to the memory of the first one. In same cases it might be a problem, which you can solve using deep copy. What do you need to create a deep copy?
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I will correct this now. If someone has a reference that says that "trivial copy constructors" are defined as being just bitwise copies, please add that explanation (or give me the reference and I will add it).
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A copy constructor is called whenever a new variable is created from an object. This happens in the following cases (but not in assignment).
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Hello, Isn't this page a candidate for "Articles with example C++ code" category? Can some one please edit this to reflect the same. Thanks,
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class X { public: X() { printf("X::X()\n"); } X(const X& copy_from_me) { printf("X::X(const X&)\n"); } } ... X a = X();
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I found this article with Google with hope to find hints about it, but it's not enough for me to understand it(may be i'm stupid? :) )
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Copy constructor - It creates internal dynamic data structures and makes a copy of internal data of the objects
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topics on
Knowledge (XXG). If you would like to participate, please visit the project page, where you can join
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instead the default constructor is called (and if only the copy constructor is defined, it doesn't compile).
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and is probably unnecessarily detailed for this article as well as repeating the preceeding example
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vypis(); // Prints 3 - that's because i have made a deep copy return 0; }
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Why do we need to use & in the definition of a copy constructor? --Anonymous
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Overload assigment operator - It makes a copy of internal data of the objects
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A variable is declared which is initialized from another object, eg,
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A value parameter is initialized from its corresponding argument.
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The sentence in the introduction might need some modifications ?
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611:// Assignment operator, no constructor or copy constructor.
605:// copy constructor is used to initialize in declaration.
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Destructor - It destroys internal dynamic data structures
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I have moved this from the article because it needs work:
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Constructor - It creates internal dynamic data structures
620:// copy constructor initializes formal value parameter.
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SymbolIndexer(const SymbolIndexer& that) = delete;
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