Andrew Kennard wrote: > Hi all > > I've got the basic hang of scope of vars in Perl which is a bit > different to other languages I've used. > > Having split a large program into packages I would like to use a > global var across multiple packages. Perl does not seem to have a 'C' > type 'extern' command to say a var is declared in another package. > Perhaps it does not need one ? Would I be correct in thinking that > the %DataFromHTMLPage in the following example would always be > pointing to the same bit of memory across the packages ?
Yes, because you've used the Export module, which works in conjunction with "use" to provide "sharing" of global variables. All package (aka "global", or "symbol table") variables have a "fully-qualified" name, of the format PackageName::SymbolName. So the "full" name of your hash is: %myglob::DataFromHTMLPage You can unambiguously reference that hash from any package by using its fully qualified name. If you leave off the package name and just write %DataFromHTMLPage, then the *current* package is used. Because of the 3 lines beginning with "require Exporter", when you "use myglob" from another package, Exporter creates an "alias" to the variable back in package myglob. So, if you have the following: package Foo; use strict; use myglob; print keys %DataFromHTMLPage; The last line is referencing the hash %Foo::DataFromHTMLPage. However, because of the Exporter stuff within myglob.pm, %Foo::DataFromHTMLPage is actually an alias to %myglob::DataFromHTMLPage. So the two packages are now "sharing" the same hash. > > "myglob.pm" > package myglob; > use strict; > use CGI::Carp qw(fatalsToBrowser); > require Exporter; > our @ISA = qw(Exporter); > our @EXPORT = qw(%DataFromHTMLPage); > our %DataFromHTMLPage; > --------------------------------- > "myscript.pl" > use strict; > use CGI::Carp qw(fatalsToBrowser); > use myglob; > use mypkg1; > use mypkg2; > > # load data into %DataFromHTMLPage and do stuff with it > -------------------------------------- > "mypkg1.pm" > package mypkg1; > use strict; > use CGI::Carp qw(fatalsToBrowser); > use myglob; > #Do stuff here with %DataFromHTMLPage using functions etc > ----------------------------------------- > "mypkg2.pm" > package mypkg2; > use strict; > use CGI::Carp qw(fatalsToBrowser); > use myglob; > #Do stuff here with %DataFromHTMLPage using functions etc > > > If I don't "use myglob" in the package files then strict causes an > error to say that %DataFromHTMLPage is undefined. Yes, because variables imported (via Exporter) get a "free pass" from use strict. > > My main question is if you define a var with 'our' if there is a > 2nd/3rd occurance of the definition of it what happens ? Nothing really. "our" is just a declaration that says "let me use this variable name without the full package qualifier from here to the end of the enclosing block or file". -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response>
