Re: Non-static singleton setup to control life time

From:

Francis Glassborow <francis.glassborow@btinternet.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Mon, 14 Dec 2009 18:29:02 CST

Message-ID:

<lLSdnbAA_aehBbvWnZ2dnUVZ8jqdnZ2d@bt.com>

Kris Prad wrote:

I want to setup a singleton, without 'static' initialization. My
motive is to control the life time of the Singleton, bounded by its
scope, something I cannot do with the statics.

Not this way. This uses static:

Single* Get()
{
   Static Single s; // do not want static
   Return &s;
}

Instead, I am doing this (please ignore thread safety issues)
Single* g_Single = NULL; // global singleton ptr
struct Single
{

    Single()
    {
        if (!g_Single)
        {
            g_Single = this;
        }
        else
        {
           throw string("Single is a singleton");
        }
    }
    ~Single()
    {
        g_Single = NULL;
    }
};

Is this ugly or acceptable?

Kris

What is wrong with this:

class Single {
public:
    Single(){
       if(exists) throw("You can only have one object of type Single");
       exists = true;
       // do rest
    }
    ~Single() { exists = false }
// rest of interface
private:
    static bool exists;
// rest of private interface etc.
};

bool Single::exists(false);

The trouble with your use of a global variable is that it could be
accidentally modified and the compiler will not be able to help you.

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