Doubts regarding memmory allocation

Question

0.00/5 (No votes)

See more:

Hi All,

If we declare a variable (int a;), is there any memory allocated to the variable at this declaration time?

And also if we declare a class pointer (MyClass *ptr) any amount of static memory allocated to 'ptr' to store the address of the dynamically created memory (ptr = new MyClass()) on this declaration time?

Thanks a lot in advance...

Posted 18-Oct-11 18:28pm

Silju MC

Updated 18-Oct-11 18:43pm

v2

Add a Solution

4 solutions

Solution 4

There are several types of memory, but, as a programmer, you only have to deal with two types: the 'stack' and the 'heap'.

The stack is memory that your compiler will take care of. Variables such as pointers or ints declared as local parameters in a function will be stored there. This memory usually will be allocated the moment your function gets called (but the compiler may occasonally handle this otherwise), and will be released the moment your function returns. You cannot do much regarding how the compiler treats this, but some compiler settings may subtly change the behaviour.

The heap is the memory that you can access programatically. Any amount of memory that you allocate dynamically using new statements will be allocated there, and it is your responsibility to release that memory later, using delete (or delete []).

So, to answer your question, both the int and pointer variables you mentioned would be allocated on the stack, every time the function is called that declares them, and the memory will be released once your function returns. If the variables are declared global however, the memory will be allocated upon starting the application, and released upon exiting (this is just one more reason not to use global variables!).

If you declare static variables inside a function, they will mostly behave like global variables, but allocating the memory required for them may be postponed until the function is called for the first time. The memory will still remain in use until the application exits.

Posted 18-Oct-11 23:59pm

Stefan_Lang

Updated 19-Oct-11 0:07am

v2

Comments

Sergey Alexandrovich Kryukov 19-Oct-11 11:23am

Some good points here, but a programmer also deals with the memory reserved for static variables. I voted 4.
--SA

Stefan_Lang 19-Oct-11 11:31am

I mentioned static variables in the last paragraph. Or did you consider that information inaccurate?

Simon Bang Terkildsen 19-Oct-11 11:30am

Got my 5

Solution 1

Hi

When we declare a variable the memory allocated in the stack memory and its removed automaticaly based on the scope of the variable

And the secon case When the object is created that time memory allocated in the heap. its we can handle programmatically also

thanx

Posted 18-Oct-11 18:56pm

shijuse

Solution 3

And it gets even better. If your variable is of local scope (dynamically alloced on the stack) then the compiler's optimization phase may decide, based on the usage of the variable, that it does not need any physical memory at all and optimize it into processor registers. This, of course, only applies to simple data types and not to class objects (but could apply to pointers to class objects). Playing the "find the memory location" game can be fun.

Posted 18-Oct-11 23:18pm

Chuck O'Toole

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2011-10-18T20:34:00

First, what is "declaration time"? Some memory is allocated by the loader of you application, some is additionally allocated during run time. It depends on what is your variable. It can be static and allocated by the loaded is some section of memory dedicated to static data. It can be "segment", some pages of pages memory, etc., depending on system architecture. Stack variable is allocated on stack, but the stack itself is allocated when its thread is created, as a phase of loading of application in case of main (starting) thread and during run time for threads created during run time.

Now, about the object of the class allocated on heap… Not just heap is involved: there are two different parts of this object: the variable points to the pointer, and the pointer points to the memory in heap where "object itself" is placed. So, the memory referenced by the pointer is, yes, allocated in heap, but the pointer itself is placed in memory exactly as in the case of integer variables, as described above. But on the top of it, a pointer can be allocated in heap itself. Simple example: a pointer can be a member of other class. And the pointer to the object of that class&hellop; well, you understand… :-)

—SA