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Ein Copy-Konstruktor ist ein überladen Konstruktor, der zum Deklarieren und Initialisieren eines Objekts von einem anderen Objekt aus verwendet wird.

Es gibt zwei Arten von Kopierkonstruktoren:

Standard-Kopierkonstruktor:Der Compiler definiert den Standardkopierkonstruktor. Wenn der Benutzer keinen Kopierkonstruktor definiert, stellt der Compiler seinen Konstruktor bereit.Benutzerdefinierter Konstruktor:Der Programmierer definiert den benutzerdefinierten Konstruktor.

Syntax des benutzerdefinierten Kopierkonstruktors:

 Class_name(const class_name &old_object); 

Betrachten Sie die folgende Situation:

stlc

 class A { A(A &x) // copy constructor. { // copyconstructor. } } 

Im obigen Fall gilt: Der Kopierkonstruktor kann auf folgende Weise aufgerufen werden:

Sehen wir uns ein einfaches Beispiel des Kopierkonstruktors an.

// Programm des Kopierkonstruktors.

 #include using namespace std; class A { public: int x; A(int a) // parameterized constructor. { x=a; } A(A &amp;i) // copy constructor { x = i.x; } }; int main() { A a1(20); // Calling the parameterized constructor. A a2(a1); // Calling the copy constructor. cout&lt; <a2.x; return 0; } < pre> <p> <strong>Output:</strong> </p> <pre> 20 </pre> <h2>When Copy Constructor is called</h2> <p>Copy Constructor is called in the following scenarios:</p> <ul> <li>When we initialize the object with another existing object of the same class type. For example, Student s1 = s2, where Student is the class.</li> <li>When the object of the same class type is passed by value as an argument.</li> <li>When the function returns the object of the same class type by value.</li> </ul> <h2>Two types of copies are produced by the constructor:</h2> <ul> <li>Shallow copy</li> <li>Deep copy</li> </ul> <h2>Shallow Copy</h2> <ul> <li>The default copy constructor can only produce the shallow copy.</li> <li>A Shallow copy is defined as the process of creating the copy of an object by copying data of all the member variables as it is.</li> </ul> <p>Let&apos;s understand this through a simple example:</p> <pre> #include using namespace std; class Demo { int a; int b; int *p; public: Demo() { p=new int; } void setdata(int x,int y,int z) { a=x; b=y; *p=z; } void showdata() { std::cout &lt;&lt; &apos;value of a is : &apos; &lt; <a<< std::endl; std::cout << 'value of b is : ' < <b<< *p <<*p<< } }; int main() { demo d1; d1.setdata(4,5,7); d2="d1;" d2.showdata(); return 0; pre> <p> <strong>Output:</strong> </p> <pre> value of a is : 4 value of b is : 5 value of *p is : 7 </pre> <img src="//techcodeview.com/img/c-tutorial/75/c-copy-constructor-3.webp" alt="C++ Copy Constructor"> <p>In the above case, a programmer has not defined any constructor, therefore, the statement <strong>Demo d2 = d1;</strong> calls the default constructor defined by the compiler. The default constructor creates the exact copy or shallow copy of the existing object. Thus, the pointer p of both the objects point to the same memory location. Therefore, when the memory of a field is freed, the memory of another field is also automatically freed as both the fields point to the same memory location. This problem is solved by the <strong>user-defined constructor</strong> that creates the <strong>Deep copy</strong> .</p> <h2>Deep copy</h2> <p>Deep copy dynamically allocates the memory for the copy and then copies the actual value, both the source and copy have distinct memory locations. In this way, both the source and copy are distinct and will not share the same memory location. Deep copy requires us to write the user-defined constructor.</p> <p>Let&apos;s understand this through a simple example.</p> <pre> #include using namespace std; class Demo { public: int a; int b; int *p; Demo() { p=new int; } Demo(Demo &amp;d) { a = d.a; b = d.b; p = new int; *p = *(d.p); } void setdata(int x,int y,int z) { a=x; b=y; *p=z; } void showdata() { std::cout &lt;&lt; &apos;value of a is : &apos; &lt; <a<< std::endl; std::cout << 'value of b is : ' < <b<< *p <<*p<< } }; int main() { demo d1; d1.setdata(4,5,7); d2="d1;" d2.showdata(); return 0; pre> <p> <strong>Output:</strong> </p> <pre> value of a is : 4 value of b is : 5 value of *p is : 7 </pre> <img src="//techcodeview.com/img/c-tutorial/75/c-copy-constructor-4.webp" alt="C++ Copy Constructor"> <p>In the above case, a programmer has defined its own constructor, therefore the statement <strong>Demo d2 = d1;</strong> calls the copy constructor defined by the user. It creates the exact copy of the value types data and the object pointed by the pointer p. Deep copy does not create the copy of a reference type variable.</p> <h2>Differences b/w Copy constructor and Assignment operator(=)</h2> <table class="table"> <tr> <th>Copy Constructor</th> <th>Assignment Operator</th> </tr> <tr> <td>It is an overloaded constructor.</td> <td>It is a bitwise operator.</td> </tr> <tr> <td>It initializes the new object with the existing object.</td> <td>It assigns the value of one object to another object.</td> </tr> <tr> <td>Syntax of copy constructor: <br> Class_name(const class_name &amp;object_name) <br> { <br> // body of the constructor. <br> }</td> <td>Syntax of Assignment operator: <br> Class_name a,b; <br> b = a;</td> </tr> <tr> <td><ul> <li>The <strong>copy constructor</strong> is invoked when the new object is initialized with the existing object.</li> <li>The object is passed as an argument to the function.</li> <li>It returns the object.</li> </ul></td> <td>The <strong>assignment operator</strong> is invoked when we assign the existing object to a new object.</td> </tr> <tr> <td>Both the existing object and new object shares the different memory locations.</td> <td>Both the existing object and new object shares the same memory location.</td> </tr> <tr> <td>If a programmer does not define the copy constructor, the compiler will automatically generate the implicit default copy constructor. </td> <td>If we do not overload the &apos;=&apos; operator, the bitwise copy will occur.</td> </tr> </table> <hr></a<<></pre></a<<></pre></a2.x;>

Wenn der Copy Constructor aufgerufen wird

Copy Constructor wird in den folgenden Szenarios aufgerufen:

• Wenn wir das Objekt mit einem anderen vorhandenen Objekt desselben Klassentyps initialisieren. Beispiel: Student s1 = s2, wobei Student die Klasse ist.
• Wenn das Objekt desselben Klassentyps als Wert als Argument übergeben wird.
• Wenn die Funktion das Objekt desselben Klassentyps nach Wert zurückgibt.

Der Konstruktor erstellt zwei Arten von Kopien:

• Flache Kopie
• Tiefe Kopie

Flache Kopie

• Der Standardkopierkonstruktor kann nur die flache Kopie erstellen.
• Eine flache Kopie ist als der Prozess definiert, bei dem eine Kopie eines Objekts erstellt wird, indem die Daten aller Mitgliedsvariablen unverändert kopiert werden.

Lassen Sie uns dies anhand eines einfachen Beispiels verstehen:

 #include using namespace std; class Demo { int a; int b; int *p; public: Demo() { p=new int; } void setdata(int x,int y,int z) { a=x; b=y; *p=z; } void showdata() { std::cout &lt;&lt; &apos;value of a is : &apos; &lt; <a<< std::endl; std::cout << \'value of b is : \' < <b<< *p <<*p<< } }; int main() { demo d1; d1.setdata(4,5,7); d2="d1;" d2.showdata(); return 0; pre> <p> <strong>Output:</strong> </p> <pre> value of a is : 4 value of b is : 5 value of *p is : 7 </pre> <img src="//techcodeview.com/img/c-tutorial/75/c-copy-constructor-3.webp" alt="C++ Copy Constructor"> <p>In the above case, a programmer has not defined any constructor, therefore, the statement <strong>Demo d2 = d1;</strong> calls the default constructor defined by the compiler. The default constructor creates the exact copy or shallow copy of the existing object. Thus, the pointer p of both the objects point to the same memory location. Therefore, when the memory of a field is freed, the memory of another field is also automatically freed as both the fields point to the same memory location. This problem is solved by the <strong>user-defined constructor</strong> that creates the <strong>Deep copy</strong> .</p> <h2>Deep copy</h2> <p>Deep copy dynamically allocates the memory for the copy and then copies the actual value, both the source and copy have distinct memory locations. In this way, both the source and copy are distinct and will not share the same memory location. Deep copy requires us to write the user-defined constructor.</p> <p>Let&apos;s understand this through a simple example.</p> <pre> #include using namespace std; class Demo { public: int a; int b; int *p; Demo() { p=new int; } Demo(Demo &amp;d) { a = d.a; b = d.b; p = new int; *p = *(d.p); } void setdata(int x,int y,int z) { a=x; b=y; *p=z; } void showdata() { std::cout &lt;&lt; &apos;value of a is : &apos; &lt; <a<< std::endl; std::cout << \'value of b is : \' < <b<< *p <<*p<< } }; int main() { demo d1; d1.setdata(4,5,7); d2="d1;" d2.showdata(); return 0; pre> <p> <strong>Output:</strong> </p> <pre> value of a is : 4 value of b is : 5 value of *p is : 7 </pre> <img src="//techcodeview.com/img/c-tutorial/75/c-copy-constructor-4.webp" alt="C++ Copy Constructor"> <p>In the above case, a programmer has defined its own constructor, therefore the statement <strong>Demo d2 = d1;</strong> calls the copy constructor defined by the user. It creates the exact copy of the value types data and the object pointed by the pointer p. Deep copy does not create the copy of a reference type variable.</p> <h2>Differences b/w Copy constructor and Assignment operator(=)</h2> <table class="table"> <tr> <th>Copy Constructor</th> <th>Assignment Operator</th> </tr> <tr> <td>It is an overloaded constructor.</td> <td>It is a bitwise operator.</td> </tr> <tr> <td>It initializes the new object with the existing object.</td> <td>It assigns the value of one object to another object.</td> </tr> <tr> <td>Syntax of copy constructor: <br> Class_name(const class_name &amp;object_name) <br> { <br> // body of the constructor. <br> }</td> <td>Syntax of Assignment operator: <br> Class_name a,b; <br> b = a;</td> </tr> <tr> <td><ul> <li>The <strong>copy constructor</strong> is invoked when the new object is initialized with the existing object.</li> <li>The object is passed as an argument to the function.</li> <li>It returns the object.</li> </ul></td> <td>The <strong>assignment operator</strong> is invoked when we assign the existing object to a new object.</td> </tr> <tr> <td>Both the existing object and new object shares the different memory locations.</td> <td>Both the existing object and new object shares the same memory location.</td> </tr> <tr> <td>If a programmer does not define the copy constructor, the compiler will automatically generate the implicit default copy constructor. </td> <td>If we do not overload the &apos;=&apos; operator, the bitwise copy will occur.</td> </tr> </table> <hr></a<<></pre></a<<>

Im obigen Fall hat ein Programmierer keinen Konstruktor definiert, daher die Anweisung Demo d2 = d1; ruft den vom Compiler definierten Standardkonstruktor auf. Der Standardkonstruktor erstellt die exakte Kopie oder flache Kopie des vorhandenen Objekts. Somit zeigen die Zeiger p beider Objekte auf denselben Speicherort. Wenn daher der Speicher eines Felds freigegeben wird, wird automatisch auch der Speicher eines anderen Felds freigegeben, da beide Felder auf denselben Speicherort verweisen. Dieses Problem wird durch die gelöst Benutzerdefinierter Konstruktor das schafft die Tiefe Kopie .

Tiefe Kopie

Deep Copy weist dynamisch den Speicher für die Kopie zu und kopiert dann den tatsächlichen Wert. Sowohl die Quelle als auch die Kopie haben unterschiedliche Speicherorte. Auf diese Weise sind sowohl die Quelle als auch die Kopie unterschiedlich und teilen sich nicht denselben Speicherort. Deep Copy erfordert, dass wir den benutzerdefinierten Konstruktor schreiben.

in SQL gegossen

Lassen Sie uns dies anhand eines einfachen Beispiels verstehen.

 #include using namespace std; class Demo { public: int a; int b; int *p; Demo() { p=new int; } Demo(Demo &amp;d) { a = d.a; b = d.b; p = new int; *p = *(d.p); } void setdata(int x,int y,int z) { a=x; b=y; *p=z; } void showdata() { std::cout &lt;&lt; &apos;value of a is : &apos; &lt; <a<< std::endl; std::cout << \'value of b is : \' < <b<< *p <<*p<< } }; int main() { demo d1; d1.setdata(4,5,7); d2="d1;" d2.showdata(); return 0; pre> <p> <strong>Output:</strong> </p> <pre> value of a is : 4 value of b is : 5 value of *p is : 7 </pre> <img src="//techcodeview.com/img/c-tutorial/75/c-copy-constructor-4.webp" alt="C++ Copy Constructor"> <p>In the above case, a programmer has defined its own constructor, therefore the statement <strong>Demo d2 = d1;</strong> calls the copy constructor defined by the user. It creates the exact copy of the value types data and the object pointed by the pointer p. Deep copy does not create the copy of a reference type variable.</p> <h2>Differences b/w Copy constructor and Assignment operator(=)</h2> <table class="table"> <tr> <th>Copy Constructor</th> <th>Assignment Operator</th> </tr> <tr> <td>It is an overloaded constructor.</td> <td>It is a bitwise operator.</td> </tr> <tr> <td>It initializes the new object with the existing object.</td> <td>It assigns the value of one object to another object.</td> </tr> <tr> <td>Syntax of copy constructor: <br> Class_name(const class_name &amp;object_name) <br> { <br> // body of the constructor. <br> }</td> <td>Syntax of Assignment operator: <br> Class_name a,b; <br> b = a;</td> </tr> <tr> <td><ul> <li>The <strong>copy constructor</strong> is invoked when the new object is initialized with the existing object.</li> <li>The object is passed as an argument to the function.</li> <li>It returns the object.</li> </ul></td> <td>The <strong>assignment operator</strong> is invoked when we assign the existing object to a new object.</td> </tr> <tr> <td>Both the existing object and new object shares the different memory locations.</td> <td>Both the existing object and new object shares the same memory location.</td> </tr> <tr> <td>If a programmer does not define the copy constructor, the compiler will automatically generate the implicit default copy constructor. </td> <td>If we do not overload the &apos;=&apos; operator, the bitwise copy will occur.</td> </tr> </table> <hr></a<<>

Im obigen Fall hat ein Programmierer seinen eigenen Konstruktor definiert, also die Anweisung Demo d2 = d1; ruft den vom Benutzer definierten Kopierkonstruktor auf. Es erstellt die exakte Kopie der Werttypdaten und des Objekts, auf das der Zeiger p zeigt. Deep Copy erstellt keine Kopie einer Referenztypvariablen.

Unterschiede s/w Kopierkonstruktor und Zuweisungsoperator (=)