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Every class requires at least one constructor, the copy constructor. It is implied if not declared. If no constructors are declared, a default constructor is also implied. Every class also requires a destructor, which is also implied if not declared.
The purpose of constructors is to construct the object (obviously) but by defining your own you can control how the object is constructed, and how member variables are initialised. By overloading constructors, you allow instances of your object to be constructed in several different ways.
The copy constructor's default implementation performs a member-wise copy (a shallow-copy) of all the class members. If your class includes pointers, you will invariably need to provide your own copy constructor to ensure that memory is deep-copied. That is, you'll want to copy the memory being pointed at, not the pointers themselves (otherwise all copies end up pointing to the same memory, which could spell disaster when one of those instances is destroyed).
The destructor allows you to tear-down your class in a controlled manner, including cleaning up any memory allocated to it. If your class includes pointers to allocated memory, you must remember to delete those pointers during destruction. The destructor is your last-chance to do so before the memory "leaks". The implied destructor will not do this for you -- you must implement one yourself.
class foo
{
public:
foo(){} // Default constructor.
foo(const foo & f){} // Copy constructor.
~foo(){} // Destructor.
};
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What is the difference between default constructor and parameterized constructor?
A default constructor is one that has no parameters (C++ also calls constructors with all default parameters a default constructor), while a parameterized constructor is one that has at least one parameter without a default value. Default constructors can be provided by the compiler if no other constructors are defined for that class or any class the class inherits from, while parameterized constructors must always be defined by the developer.
When a object is passed to a function as argument why it is not generating an error if the parameterized constructor is defined and not the default constructor?
default constructor is used only when the programmer does not use a constructor to initialize objects. Once the programmer defines a constructor then the default constructor is no longer used
True or False A C plus plus class constructor cannot return a function value?
True - A C++ constructor cannot return a value.
What is the difference between implicit and explicit call of constructor in c plus plus?
An implicit constructor call will always call the default constructor, whereas explicit constructor calls allow to chose the best constructor and passing of arguments into the constructor.
What is mean constructor in java?
A parameterized constructor in java is just a constructor which take some kind of parameter (variable) when is invoked. For example. class MyClass { //this is a normal constructor public MyClass(){ //do something } //this is a parameterized constructor public MyClass(int var){ //do something } //this is another parameterized constructor public MyClass(String var, Integer var2){ //do something } }
