Static variables in C++ Post: 302741087

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Top Forums Programming Static variables in C++ Post 302741087 by Don Cragun on Friday 7th of December 2012 11:18:35 AM

12-07-2012

Registered User

Quote:

Originally Posted by JohnGraham

Wish granted: Your mildly cryptic and explanation-devoid statement simply compels me to ask, what part of the above do you think may be associated with undefined behaviour?

I have to say, posting such a statement only seems designed to confuse the original poster without explaining much...

If the application is assuming that based on the location in memory of dl (&dl) it "knows" the address of df or du and makes use of that knowledge to get the value of df or to store a value into du that application will produce undefined results. This is true even though there is a good chance that with a little testing the user can figure out how a given compiler will arrange the locations of the integers declared by:

Code:

static int  df, dl, du, count;

or by:

Code:

static int  df;
static int  dl;
static int  du;
static int  count;

There is probably a much better than 50% chance that the two above ways of declaring these variables will result in them being allocated in the same positions relative to each other, but there is a non-zero percent chance that some compilers would allocate them in reverse order (or alphabetic order by name or some other order) in memory.

Any application that makes an assumption like this is depending on undefined behavior. As Corona688 said:

Quote:

Without seeing what he's done, it's hard to explain what he's done.

Is it possible that an assumption like this could change the behavior of a section of code? Absolutely.
Is it likely that an assumption like this would change the behavior of a section of code? Who knows?

Last edited by Don Cragun; 12-07-2012 at 12:20 PM.. Reason: fixed typo

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SoAnnoText3CharOrientElement(3) 				       Coin					   SoAnnoText3CharOrientElement(3)

NAME

       SoAnnoText3CharOrientElement -

       The SoAnnoText3CharOrientElement class is yet to be documented.

       FIXME: write doc.

SYNOPSIS

       #include <Inventor/elements/SoAnnoText3CharOrientElement.h>

       Inherits SoInt32Element.

   Public Member Functions
       virtual void init (SoState *state)
	   FIXME: write doc.

   Static Public Member Functions
       static SoType getClassTypeId (void)
       static int getClassStackIndex (void)
       static void * createInstance (void)
       static void initClass (void)
       static void set (SoState *const state, SbBool isOriented)
	   FIXME: write doc.
       static SbBool get (SoState *state)
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       static SbBool getDefault (void)
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   Protected Member Functions
       virtual ~SoAnnoText3CharOrientElement ()

   Additional Inherited Members
Detailed Description
       The SoAnnoText3CharOrientElement class is yet to be documented.

       FIXME: write doc.

Constructor &; Destructor Documentation
   SoAnnoText3CharOrientElement::~SoAnnoText3CharOrientElement (void) [protected],  [virtual]
       The destructor.

Member Function Documentation
   SoType SoAnnoText3CharOrientElement::getClassTypeId (void) [static]
       This static method returns the class type.

       Reimplemented from SoInt32Element.

   int SoAnnoText3CharOrientElement::getClassStackIndex (void) [static]
       This static method returns the state stack index for the class.

       Reimplemented from SoInt32Element.

   void * SoAnnoText3CharOrientElement::createInstance (void) [static]
       This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

   void SoAnnoText3CharOrientElement::initClass (void) [static]
       This static method initializes static data for the SoAnnoText3CharOrientElement class.

       Reimplemented from SoInt32Element.

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Version 3.1.3							  Wed May 23 2012				   SoAnnoText3CharOrientElement(3)