C header file and extern Post: 302851859

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Top Forums Programming C header file and extern Post 302851859 by tornow on Tuesday 10th of September 2013 12:11:34 AM

09-10-2013

Registered User

Thanks. Your explanation and example makes it more clear (also thanks for pointing out it may not be best praxis, but for now i just try to understand the general idea).

I think you say that: header files are (or can be ) used _instead of declaring the variable foo as extern in File2 and File3. foo is defined in File1 (and storage is set aside for it). File1 includes myheader.h too, and if foo is declared (File2 and File3) or defined (File1) is decided by the #ifndef Mainfile and #define Mainfile in File1.

I read in �The C Programming langauge"; (As "C A modern approach" was not clear on the subject) and in chapter 1 "External variables and scope" (page 33 for me) it says the following (or that is what i understand):
- a definition creates a variable and sets aside storage
- a declaration only announces the nature of a variable
- extern says that the definition is elsewhere and only declares
- header files include declarations, not definitions
Is both correct (What i understood of your post and what i understood of the book)?

I think i am getting closer to understand it. Let me rethink and read again.Really thanks.

tornow

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perl::critic::policy::valuesandexpressions::prohibitmixedboolean

Perl::Critic::Policy::ValuesAndExpressions::ProhibitMixeUserlContribPerl::Critic::Policy::ValuesAndExpressions::ProhibitMixedBooleanOperators(3pm)

NAME

       Perl::Critic::Policy::ValuesAndExpressions::ProhibitMixedBooleanOperators - Write " !$foo && $bar || $baz " instead of " not $foo && $bar
       or $baz".

AFFILIATION

       This Policy is part of the core Perl::Critic distribution.

DESCRIPTION

       Conway advises against combining the low-precedence booleans ( "and or not" ) with the high-precedence boolean operators ( "&& || !" ) in
       the same expression.  Unless you fully understand the differences between the high and low-precedence operators, it is easy to misinterpret
       expressions that use both.  And even if you do understand them, it is not always clear if the author actually intended it.

	   next if not $foo || $bar;  #not ok
	   next if !$foo || $bar;     #ok
	   next if !( $foo || $bar ); #ok

CONFIGURATION

       This Policy is not configurable except for the standard options.

AUTHOR

       Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>

COPYRIGHT

       Copyright (c) 2005-2011 Imaginative Software Systems.  All rights reserved.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.  The full text of this license
       can be found in the LICENSE file included with this module.

perl v5.14.2							    Perl::Critic::Policy::ValuesAndExpressions::ProhibitMixedBooleanOperators(3pm)