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Full Discussion: Static variables in C++
Top Forums Programming Static variables in C++ Post 302741095 by achenle on Friday 7th of December 2012 11:38:56 AM
Old 12-07-2012
Quote:
Originally Posted by Don Cragun
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:

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?
Saying code like that "depend[s] on undefined behavior" is too kind. Anyone who writes code that assumes the location of a variable based on the location of another variable is bat-!*()% crazystupid.

FWIW, multiple definitions on one line are a bad idea for other reasons, too.

What's this mean:
Code:
char* ptrA, ptrB;

 

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LEARN ABOUT MOJAVE

locale::codes::langext

Locale::Codes::LangExt(3pm)				 Perl Programmers Reference Guide			       Locale::Codes::LangExt(3pm)

NAME

       Locale::Codes::LangExt - standard codes for language extension identification

SYNOPSIS

	  use Locale::Codes::LangExt;

	  $lext = code2langext('acm');		       # $lext gets 'Mesopotamian Arabic'
	  $code = langext2code('Mesopotamian Arabic'); # $code gets 'acm'

	  @codes   = all_langext_codes();
	  @names   = all_langext_names();

DESCRIPTION

       The "Locale::Codes::LangExt" module provides access to standard codes used for identifying language extensions, such as those as defined in
       the IANA language registry.

       Most of the routines take an optional additional argument which specifies the code set to use. If not specified, the default IANA language
       registry codes will be used.

SUPPORTED CODE SETS

       There are several different code sets you can use for identifying language extensions. A code set may be specified using either a name, or
       a constant that is automatically exported by this module.

       For example, the two are equivalent:

	  $lext = code2langext('acm','alpha');
	  $lext = code2langext('acm',LOCALE_LANGEXT_ALPHA);

       The codesets currently supported are:

       alpha
	   This is the set of three-letter (lowercase) codes from the IANA language registry, such as 'acm' for Mesopotamian Arabic.

	   This is the default code set.

ROUTINES

       code2langext ( CODE [,CODESET] )
       langext2code ( NAME [,CODESET] )
       langext_code2code ( CODE ,CODESET ,CODESET2 )
       all_langext_codes ( [CODESET] )
       all_langext_names ( [CODESET] )
       Locale::Codes::LangExt::rename_langext  ( CODE ,NEW_NAME [,CODESET] )
       Locale::Codes::LangExt::add_langext  ( CODE ,NAME [,CODESET] )
       Locale::Codes::LangExt::delete_langext  ( CODE [,CODESET] )
       Locale::Codes::LangExt::add_langext_alias  ( NAME ,NEW_NAME )
       Locale::Codes::LangExt::delete_langext_alias  ( NAME )
       Locale::Codes::LangExt::rename_langext_code  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangExt::add_langext_code_alias  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangExt::delete_langext_code_alias  ( CODE [,CODESET] )
	   These routines are all documented in the Locale::Codes::API man page.

SEE ALSO

       Locale::Codes
	   The Locale-Codes distribution.

       Locale::Codes::API
	   The list of functions supported by this module.

       http://www.iana.org/assignments/language-subtag-registry
	   The IANA language subtag registry.

AUTHOR

       See Locale::Codes for full author history.

       Currently maintained by Sullivan Beck (sbeck@cpan.org).

COPYRIGHT

	  Copyright (c) 2011-2013 Sullivan Beck

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.18.2							    2013-11-04					       Locale::Codes::LangExt(3pm)
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