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----- Original Message ----- 
From: "Girish BR" 
To: 
Sent: Thursday, June 17, 2004 6:10 PM
Subject: [UTTARA] Static Variable


> Why is a static variable stored in a Heap??
    
    This is a VERY general assumption you have made that the static variables 
are stored in the heap.  As far as I know, they are stored in the data section
of the process.  Here is an approximate picture:

         ____________
        |   Stack    |  (Stack grows downwards)
        |............|
        |            |
        |            |
        |            |
        |............|
        |    Heap    |  (Heap grows upwards)
         ------------
        |   Static   |  (also called data-section)
         ------------
        |  Constants |
         ------------
        |    Text    |
         ------------

    The C programming language defines 3 storage types: automatic, static and
allocated.  

    +   Automatic(local) variables can be stored in the machine registers and
        stack.  The stack is also used for function calls.  

    +   Global variables, and/or variables defined with the static storage
        speicifier, go to the static storage.  (See the above diagram)

    +   The heap is used for the `allocated' type of storage.  When a request is
        made using either of malloc() or calloc() functions, storage is 
        allocated from the heap.  free() is used to return the memory back to
        the heap.  Now, please check if your assumptions match with this or
        not.  


> What will happen if it is stored in a stack.

    If we go by what I have written above, static variables will not be stored
in the stack.  There are few reasons, however, as why they can not (in fact, 
should not) be stored in the stack.

    +   Stack is a pretty dynamic entity.  A variable stored once in the stack
        is not required to get the same logical address the next time.  This is
        quite OK for an automatic variable.

    +   On the other hand, an object of static storage type is allocated the
        storage at the program start up.  Also note that a static object MUST
        have a fixed address through out the program execution.  A stack can
        not guarantee this behaviour.  This is why static variables are not
        stored in the stack.
 

    It must also be noted that the C Standard does not provide implementation 
details (like algorithms etc).  It only talks about the behaviour and properties
of the C language and it's constructs.  An implementor is free to choose 
whatever mechanism (i.e., data-structures, etc.) that suits his purpose, but
is required to meet all or most of the standard specifications.  So, as a
programmer we have the least to bother as where a static variable will go!