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Which class methods does the compiler generate automatically if you don't provide them explicitly?
Default constructor: X()Copy constructor: X(const X&)Copy assignment operator: X& operator=(const X&)Move constructor: X(X&&)Move assignment operator: X& operator=(XX&)Destructor: ~X()By default, the compiler will generate each of these operations if a program uses it. However, if the programmer declares any constructor for a class, the default constructor for that class is not generated. If the programmer declares a copy or move operation, no copy, move or destructor is generated. If the programmer declares a destructor, no move operation is generated (a copy constructor is generated for backward compatibility).We can also suppress generation of specific operations with the =delete pseudo-initialiser:class X {public:X (const X&) =delete; // suppress the compiler-generated copy operationsX& operator=(const X&) =delete;// ...};
What is friend constructor?
A friend constructor is a constructor that is declared a friend of another class and that grants that constructor private access to the class in which it is declared a friend. Example: class Y { friend char* X::foo (int); // friend function friend X::X (char); // constructors can be friends friend X::~X(); // destructors can be friends }; For more information, see '11.3 Friends' in the current ISO C++ Standard.
What is parameter constructor?
C++ permits us to achieve this objects bt passing argument to the constructor function when the object are created . The constructor that can take arguments are called parametrized constructors Example:- class abc { int m,n; public: abc(int x,int y); //paramererise constructor ................ ................. }; abc::abc(int x,int y) { m=x;n=y; }
How do you get a default constructor?
The default constructor is an empty (only call the super constructor) with no parameters constructor inserted by the java compiler when you don't define a constructor in your class. If you write something like this: public class NoConstructorClass{ //no constructor goes here } Then you get something like this: public class NoConstructorClass{ public NoConstructorClass(){ // Default constructor that you didn't write super(); } }
What is copy construct in c plus plus?
A copy constructor is a separate, compiler created constructor for a class. This allows the programmer to instantiate a class and copy the contents of the given class into the new class. For example: If I have a class foobar: Foobar foobar; Foobar foobar1( foobar ); The second line creates a class in the exact image of the original class, with all of its variables set the same way as the original class.
Which class methods does the compiler generate automatically if you don't provide them explicitly?
Default constructor: X()Copy constructor: X(const X&)Copy assignment operator: X& operator=(const X&)Move constructor: X(X&&)Move assignment operator: X& operator=(XX&)Destructor: ~X()By default, the compiler will generate each of these operations if a program uses it. However, if the programmer declares any constructor for a class, the default constructor for that class is not generated. If the programmer declares a copy or move operation, no copy, move or destructor is generated. If the programmer declares a destructor, no move operation is generated (a copy constructor is generated for backward compatibility).We can also suppress generation of specific operations with the =delete pseudo-initialiser:class X {public:X (const X&) =delete; // suppress the compiler-generated copy operationsX& operator=(const X&) =delete;// ...};
What is friend constructor?
A friend constructor is a constructor that is declared a friend of another class and that grants that constructor private access to the class in which it is declared a friend. Example: class Y { friend char* X::foo (int); // friend function friend X::X (char); // constructors can be friends friend X::~X(); // destructors can be friends }; For more information, see '11.3 Friends' in the current ISO C++ Standard.
What is parameter constructor?
C++ permits us to achieve this objects bt passing argument to the constructor function when the object are created . The constructor that can take arguments are called parametrized constructors Example:- class abc { int m,n; public: abc(int x,int y); //paramererise constructor ................ ................. }; abc::abc(int x,int y) { m=x;n=y; }
Is there any friend constructor in c?
C is not an object-oriented programming language so there is no friend keyword let alone friend constructors. In C++, however, constructors can be declared friends. Consider the following code where the class Y default constructor has private access to X::foo() because the Y::Y() constructor is explicitly declared a friend of class X. Note that Y must be defined before X can be defined, thus X must be forward declared. #include<iostream> class X; // fwd declaration class Y { public: Y() { X x; x.foo(); } // X::foo is private, but Y::Y() is a friend. }; class X { friend Y::Y(); // friend constructor private: void foo() {} };
How do you get a default constructor?
The default constructor is an empty (only call the super constructor) with no parameters constructor inserted by the java compiler when you don't define a constructor in your class. If you write something like this: public class NoConstructorClass{ //no constructor goes here } Then you get something like this: public class NoConstructorClass{ public NoConstructorClass(){ // Default constructor that you didn't write super(); } }
Write a program in c plus plus with constructor?
// constructor program to add two number's // program written by SuNiL kUmAr #include<iostream.h> #include<conio.h> class constructor { private: int a,b; public: constructor(int m,int n); int sum(); }; constructor::constructor(int m,int n) { a=m; b=n; } int constructor::sum() { int s; s=a+b; return (s); } int main() { int x,y; clrscr(); cout<<"enter two number's to add \n"; cin>>x>>y; class constructor k (x,y); cout<<"sum of two number's is = "<<k.sum(); getch(); return (0); }
What is copy construct in c plus plus?
A copy constructor is a separate, compiler created constructor for a class. This allows the programmer to instantiate a class and copy the contents of the given class into the new class. For example: If I have a class foobar: Foobar foobar; Foobar foobar1( foobar ); The second line creates a class in the exact image of the original class, with all of its variables set the same way as the original class.
What is a constructor initialization list?
The constructor initialisation list is the most efficient method of initialising class members, including primitive members. You use it always and without exception to ensure efficient construction. Consider the following: class foo { int m_data; public: foo(int data=0){ m_data=data; } foo(const foo& f){ m_data=f.m_data; } }; This class employs inefficient construction technique by initialising the member variables in the constructor bodies rather than the initialisation list. In other words, m_data is instantiated and initialised in two stages instead of one. It is not unlike the following two stage initialisation: int m_data; m_data =0; A more efficient way of writing these lines is to initialise at the point of instantiation using a compound statement: int m_data=0; The same applies to class construction. By using the initialisation list, member variables are initialised at the point of instantiation, as per the following: class foo { int m_data; public: foo(int data=0):m_data(data) {} foo(const foo& f):m_data(f.m_data) {} }; You will note that primitive members use object-oriented syntax in the initialisation list. This is not merely sugar-coating -- it applies to all members, including base classes. This makes it possible to invoke specific base class constructors, rather than the default constructor that would be implicitly invoked (or the base class copy constructor in the case of a derived class copy constructor). Consider the following: class base { int m_data; public: base(int data=0):m_data(data) {} base(const base& b):m_data(b.m_data) {} }; class derived : public base { public: derived(int data=0):base(data) {} derived(const derived& d):base(d) {} }; Note how the derived class default constructor invokes the base class default constructor, but passes the data argument to it. Had you not used the initialisation list you'd have to construct base, then derived, and then initialise the base class member via a setter. Clearly the initialisation list is more efficient because the base class can be initialised before derived is even instantiated, which cannot happen until the base class is fully-instantiated. Note also that the copy constructor specifically invokes the base class copy constructor. Although the argument, d, is not a base class, it is a type of base class, thus there is no need to upcast the argument. Ultimately, it can be seen that the constructor bodies are largely redundant. You still need a constructor body, even an empty one, but most of the time you will use the body for debug trace code. There will be times, however, where the class initialisation list cannot fully initialise a member because one or more arguments require more complex processing (such as calling a complex setter). In this case, you must use the constructor body. However, you must still perform as much initialisation as is possible via the initialisation list to ensure the most efficient construction method. Only those members that require additional processing need not be initialised, but it costs nothing to initialise them to an arbitrary or default value. The initialisation list is vital in the case of the copy constructor, as passing an object to a function by value will automatically invoke the copy constructor. If any member variables are embedded objects, or the object is derived from one or more base classes, then their copy constructors will be invoked as well. Therefore it pays to make construction as efficient as possible when copying objects. However, the same applies to any constructor. The more efficient the constructor performs, the better your programs will perform, especially in complex hierarchies where objects may be deeply embedded within other objects that are themselves embedded.
1 Explain the concepts of constructor and destructor Do you have to declare a constructor every time you create a class?
You only need a constructor if the default constructor will not suffice. Often times, it is useful to have a constructor that takes common parameters so that you do not have to write additional code. For example, a Point class might have a constructor for Point(int x, int y), which would be a shortcut for assigning x and y independently. Other classes may not need any default values assigned, and for this, it is acceptable to just use the default constructor. Finally, some classes are virtual, static, or abstract, and so may not need a constructor because the constructor is unnecessary (static), or may be defined elsewhere (virtual, abstract).
What is this and super keyword in java?
"this" represents current instance of a class whereas to access constructor, member variable or method of the super class "super" keyword is used. For ex. public class A { A() {} hello() {}; } public class B { private int x; B() { super(); // call A's constructor } hello(int x) { super.hello(); //calls A's hello() this.x = x; // this.x represents member variable of the class B whereas "x" represents local variable. } }
A method that is automatically called when an instance of a class is created?
The constructor of a class is automatically called when an instance of the class is created (using new in C++). The constructor method has the same name as the class that it is a part of. Constructors have no type and do not return anything. Similarly, the destructor is automatically called when the instance of the class is destroyed. The destructor is the same name as the class and is preceded by a tilde (~) For example: class Example { public: Example() // Constructor { printf("Object created\n"); } ~Example() // Destructor { printf("Object destroyed\n") } }; int main() { Example* x = new Example(); // Creates object, calls constructor delete x; // Calls destructor, deletes object return 0; }
How do you call constructor?
Constructors in java cannot be invoked explicitly. They are invoked automatically when an object is created. In java if u dont write any code for constructor, by default compiler inserts a zero argument constructor. If required, it can be overrided.
