Default constuctor

[Tapeesh]

Does C++ say that a default constructor needs to be generated by the
compiler even if a class has the default constructor defined ? Say for
eg. there is a class

class A
{

int i;
A()
{
i=0;
}
};


class B
{
int i;
void foo()
{
i=0;
}
};

In this case will the compiler generate its own default constructor for
class A like in the case of class B and also create the one defined
in the class ? If yes, then what is the functionality of this compiler
generated constructor.

 

[Gary Labowitz]

Does C++ say that a default constructor needs to be generated by the
compiler even if a class has the default constructor defined ? Say for
eg. there is a class

<<snip>>
No. Once you supply a consstructor the compiler will not provide one.

 

[John Carson]

Does C++ say that a default constructor needs to be generated by the
compiler even if a class has the default constructor defined ? Say for
eg. there is a class

class A
{

int i;
A()
{
i=0;
}
};


class B
{
int i;
void foo()
{
i=0;
}
};

In this case will the compiler generate its own default constructor
for class A like in the case of class B and also create the one
defined in the class ? If yes, then what is the functionality of this
compiler generated constructor.

The compiler will NOT generate a default constructor if you define ANY
constructor for a class. Consider for example:

class A
{
int i;
public:
A(int n)
{
i=n;
}
};

This doesn't have a default constructor. Thus if you write:

int main()
{
A a;
}

then it won't compile because

A a;

requires a default constructor and class A does not have one. If you change
it to, say,

A a(5);

then it compiles without a problem.

Incidentally, your original class declaration:

class A
{
int i;
A()
{
i=0;
}
};

has a private constructor, so

A a;

won't compile. You need to make the constructor public.

 

[Tapeesh]

The compiler will NOT generate a default constructor if you define ANY
constructor for a class. Consider for example:

class A
{
int i;
public:
A(int n)
{
i=n;
}
};

This doesn't have a default constructor. Thus if you write:

int main()
{
A a;
}

then it won't compile because

A a;

requires a default constructor and class A does not have one. If you change
it to, say,

A a(5);

then it compiles without a problem.

Incidentally, your original class declaration:

class A
{
int i;
A()
{
i=0;
}
};

has a private constructor, so

A a;

won't compile. You need to make the constructor public.

What i wanted to ask is that when the compiler compiles a code at that
time while creating an object model for the source code, does the
compiler generate some default constructor even if some constructor
(default or otherwise) has been defined for the class?

 

[John Carson]

What i wanted to ask is that when the compiler compiles a code at that
time while creating an object model for the source code, does the
compiler generate some default constructor even if some constructor
(default or otherwise) has been defined for the class?

The answer has already been given twice. NO.