If we create object of a class without using new in C++, is this object is created on heap?

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Hello,
1) I know that things initialized with new are on heap. But If we create object of a class without using new in C++,

MyClass obj();

1)Where it is declared,stack or heap??
2) Where it has memory,initializes,stack or heap?

Posted 25-Jul-11 19:37pm

ahsanriaz1K

Updated 26-Jul-11 19:32pm

v3

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2 solutions

Solution 2

You have to be aware that in C++ MyClass obj(); would be a declaration of a function named obj that returns an object of type MyClass.

To actually create an object on the stack, you will have to remove the parenthesis and write:

void someFunction()
{
  MyClass obj; // object on the stack
}

Posted 26-Jul-11 13:44pm

Philippe Mori

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ahsanriaz1K 27-Jul-11 0:30am

We can declare object using MyClass obj();, it is not a function declration, and please tell me that if we will assign memory to obj in someFunction, where does this memory goes? heap or stack?

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barneyman · Accepted Answer · 2011-07-25T23:30:00

Solution 1

That object would be created on the stack, and then destroyed on the way out of the function

The Data segment is used for all variables declared outside the scope of any function

The stack is used for all variables declared within a function; in the following example

void afunction()
{
   MyClass *pMyClass=new MyClass();
}

The pointer is local to the function (on the stack) but the class is on the heap

Posted 25-Jul-11 23:30pm

barneyman

Comments

Sergey Alexandrovich Kryukov 26-Jul-11 12:39pm

My 4. More exactly, the instance of the class (object of the class type) in on the heap. Some do not understand, so the note is not redundant.
--SA

ahsanriaz1K 27-Jul-11 0:27am

@barneyman: OK, I know MyClass obj();
will be declared on stack but memory assigned to it cannot be in stack. As class objects are reference type and reference type variables have memory on heap not stack, so how this MyClass obj();
instance has its memory on stack.

Emilio Garavaglia 27-Jul-11 4:38am

There is no concept of "reference type" and "value type" in C++.
struct and class are the same (except for public vs private default member visibility)

barneyman 27-Jul-11 2:32am

unless your object explicitly, internall allocates memory from the heap with a new or a malloc call, the stack will be extended by the size of your object when the function SP/BP code kicks in

Try it in the debugger, look at the memory block at &obj, then look at the memory at ESP