Copy constructor (C++)

In the <a href="/facts/C%252B%252B/Et0F2qn9">C++</a> <a href="/facts/Programming_language/cWTYbgWa">programming language</a>, a copy constructor is a special <a href="/facts/Constructor_(computer_science)/8JNHsH5H">constructor</a> for creating a new <a href="/facts/Object_(computer_science)/eX99dtAw">object</a> <a href="/facts/Object_copy/QbBS3suW">as a copy</a> of an existing object. Copy constructors are the standard way of copying objects in C++, as opposed to <a href="/facts/Cloning_(programming)/3ShnR7RM">cloning</a>, and have C++-specific nuances.
The first argument of such a constructor is a reference to an object of the same type as is being constructed (const or non-const), which might be followed by parameters of any type (all having default values).
Normally the <a href="/facts/Compiler/WNfCDFJe">compiler</a> automatically creates a copy constructor for each <a href="/facts/Class_(computer_science)/zvzkSAtE">class</a> (known as an implicit copy constructor) but for special cases the <a href="/facts/Programmer/WGTS1Jv9">programmer</a> creates the copy constructor, known as a user-defined copy constructor. In such cases, the compiler does not create one. Hence, there is always one copy constructor that is either defined by the user or by the system.
A user-defined copy constructor is generally needed when an object owns <a href="/facts/Data_pointer/fPoNzy9b">pointers</a> or non-shareable <a href="/facts/Reference_(computer_science)/1vm2Bph1">references</a>, such as to a <a href="/facts/Computer_file/FjFH3Ufm">file</a>, in which case a <a href="/facts/Destructor_(computer_science)/gr4051ve">destructor</a> and an <a href="/facts/Assignment_operator_in_C%252B%252B/1TsvByvM">assignment operator</a> should also be written (see <a href="/facts/Rule_of_three_(C%252B%252B_programming)/VVAvmfao">Rule of three</a>).

Copy constructor (C++) open-in-new

Copy constructor (C++)