Re: Design issue

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Fri, 2 May 2008 10:21:23 -0400

Message-ID:

<fvf814$bhm$1@news.datemas.de>

Philipp.Weissenbacher@gmail.com wrote:

Hi all!

I've got something of a design issue here:

class Bucket {
public:
// Initial capacity of a bucket (= # of items in a page)
static const unsigned int M = 10;

// Key store
Key keyStore[M];

// Count of items in the bucket
int count;

// Bucket's depth (number of significant bits)
int localDepth;

Bucket();
~Bucket();
};

Now, I use Bucket in a data structure like this:

#include "Bucket.h"

Foobar::Foobar() : a(0), b(0), c(0) {
}

void Foobar buzz() {

I presume you meant

void Foobar::buzz() {

if(Bucket::M < 1)
...
}

Although this compiles just fine, if I want to use it e.g. write
something like

#include "Foobar.h"
int maint() {

'maint'?

Foobar* b = new Foobar();
}

I get a "undefined reference" from ld. Googling on this I found out
that I have one has to initialize a static variable in exactly one
compilation unit (see [10.10] Why can't I initialize my static member
data in my constructor's initialization list? by Marshall Cline).
But how do I fix this?

You need to _define_ 'Bucket::M' outside of 'Bucket' and omit the
initialiser. This is necessary because you use 'Bucket::M' outside
of the class definition. Add

const unsigned int Bucket::M;

somewhere at the namespace level in one of your C++ files (I would
assume you have the translation unit with other 'Bucket' member
functions defined, that's a good place for the 'M' definition).

V
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