C++ Programming - Constructors and Destructors - Discussion

Compile time error:- (Why), As we know constructor fired when object is created, at the same time compiler check for default constructor if you are not declare any constructor in your code, otherwise, on same time compiler ignore call for default constructor it make a call for user defined constructor.

Object is created at compile time, that's why error occur at compile time. (Some time object may be create at run time for to achieve run time polymorphism).

Constructor errors are always genrated at compile time. If we write a constructor, then compiler only deals with that constructor, not go for default constructor. So wehen we create a object having no parameter. It generates error.

#include<iostream.h>
#include<conio.h>
class bharat
{
private:
int a;
public:
bharat(int b)
{
a=b;
cout<<"values is"<<b<<endl;
}
};
int main()
{
bharat b();
getch();
return 0;
}


Guys my code is like this but I do not give any error..!

Basically that constructor error occur at compile time. But the que is that When that error occurs? The answer is when we called constructor explicitly within the body of any function then at that time compile error occur. So the answer is compile error.

But in other case. It depends on compiler also. Some compilers allow us to create a class without default constructors and it will created automatically during run time.

Why error is coming in c++?

Compile time error, because constructor error generally generated at compile time.

Compile time error. Because constructor error always generated at compile time. Compiler use to create default constructor if default constructor is not provided.

Constructor errors are always generated at compile time. If we write a constructor, the compiler only deals with that constructor, not go for default constructor. So when we create a object having no parameter. It generates error.

Output : Compile-time error

Explanation: By default Compiler provides zero argument constructor & copy constructor implicitly, if we not define them explicitly. Compiler will not call default constructor(zero argument constructor), if we define parameterized constructor explicitly. Thus creating class object without parameters gives compile time error.

Note: Default Constructor is a constructor with no parameters (or) all parameters of the constructor with default arguments.

class X
{
private:
int x;
public:
X(int m) // Parameterized constructor
{
x = m;
}
};

int main()
{
X p; // error
X q(10); // No error

return 0;
}

Solution:
(1) Define a zero argument constructor.

class X
{
private:
int x;
public:
X() // Default constructor(zero argument constructor)
{
}
X(int m) // Parameterized constructor
{
x = m;
}
};

int main()
{
X p; // No error
X q(10); // No error

return 0;
}

(2) Define a Parameterized constructor with default arguments.A constructor with all parameters having default values known as default constructor

class X
{
private:
int x;
public:
X(int m=0)// Parameterized constructor with default arguments
{
x = m;
}
};

int main()
{
X p; // No error
X q(10); // No error

return 0;
}

I agree with Naveen. Compiler use to create default constructor if default constructor is not provided.