Re: class method static variable same across isntances?

"Jim Langston" <>
Fri, 5 Oct 2007 21:32:58 -0700
"Chris ( Val )" <> wrote in message

On Oct 5, 9:26 am, "Jim Langston" <> wrote:

The output of the following program for me is:
0 1 2

Which is what I want. I just want to confirm this is well defined
that a static local variable to a class function/method is the same
across classes.

#include <iostream>
#include <vector>

class Foo
    std::vector<int>& Data( )
        static std::vector<int> EmptyData;

        return EmptyData;
    int Bar()
        static int Val = 0;
        return Val++;



Have you thought about deriving from a common base class?


class Common
 static std::vector<int> EmptyData;

 // ...


class Foo : public Common
 // ...

If you want common functionality across all instances,
it might be worth looking into something like this.

It's actually used in a method to return a reference to a set using a form
of recursion.

class PartIndex
    PartIndex( const std::string& Name = "Torso" ): Name_( Name ) {}
    // Lot of other public methods used to populate Indicies_ and Parts_
    std::set<size_t>& PartIndicies( const std::string& Name )
        static std::set<size_t> EmptySet;

        if ( Name_ == Name )
            return PartIndicies();
            for ( std::vector<PartIndex>::iterator it = Parts_.begin(); it
!= Parts_.end(); ++it )
                std::set<size_t>& ReturnSet = (*it).PartIndicies( Name );
                if ( &ReturnSet != &EmptySet )
                    return ReturnSet;
            return EmptySet;
    std::string Name_;
    std::set<size_t> Indicies_;
    std::vector<PartIndex> Parts_;


My other option would be to use a try...catch block which I am not fond of
for using for something like this.

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