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Re: calculate number of template instantiations

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On 2011-10-25 19:30:24 +0400, Noah Roberts said:

> On Oct 25, 6:32 am, Victor Bazarov <v.baza...@comcast.invalid> wrote:
>> On 10/25/2011 9:04 AM, Ruslan Mullakhmetov wrote:
>> 
>>> I got an interesting problem to play with templates. It's not abstract
>>> and come from real life. I'm not sure wether it has solution within C++,
>>> so I need advise and you opinions.
>> 
>>> In brief: I need to calculate number of template instantiation,
>>> reasoning below.
>> 
>>> What I need. Assume I have some template Templ<T>. In the code I
>>> instantiated it several times like Templ<A>, Templ<B>, ... Next I need
>>> to get number of instantiation _prior_ to creating any of instances of
>>> instantiated types. The code, I believe, clarify. Note, it's not compiling.
>>> [...]
>> 
>> A static data member in a template would be instantiated once per every
>> template instantiation and initialized once.  If that data member is of,
>> say, 'int' type, you can initialize it by calling some function in which
>> the counter would sit.  Pass an argument to that function to indicate
>> whether to increment the counter before returning it or just return what
>> it has.
> 
> This is close except that template members that are never used do not
> make it into existence.  Thus unless you actually use that static
> member somewhere, it never gets initialized and thus never increases
> the count.  Since the goal here is to make a count variable, not an ID
> or whatever, I imagine this problem is going to come up.
> 
> One way to solve this problem is to use the static variable to
> initialize a non-static variable within the constructor(s) of the
> object.  I don't believe you actually have to use the instance member
> beyond its use in the constructor, but I actually had a use for it as
> an ID.
> 
> See this SO entry:
> http://stackoverflow.com/questions/4383602/how-to-force-inclusion-of-unused-object-definitions-in-a-library 
> 

Yes, I got it. I temporaly solved it by streaming value to cout. Thank 
you to. now i use useless class.

the code:

size_t counter( size_t size, bool count );
//extern size_t g_hack;


template<typename T>
class Templ
{
	class UseMe
	{
	public:
		UseMe( size_t sz )
		{
			
		}
	};	
	
	T _val;
	UseMe _useme;
public:
	
	Templ<T>(): _useme(size_counter)
	{
	}
public:
	static size_t size_counter;
};

template<typename T>
size_t Templ<T>::size_counter = counter(sizeof(T), true);

#endif
-- 
BR, Ruslan Mullakhmetov

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Thread

calculate number of template instantiations Ruslan Mullakhmetov <tiabaldu@gmail.com> - 2011-10-25 17:04 +0400
  Re: calculate number of template instantiations Victor Bazarov <v.bazarov@comcast.invalid> - 2011-10-25 09:32 -0400
    Re: calculate number of template instantiations Noah Roberts <roberts.noah@gmail.com> - 2011-10-25 08:30 -0700
      Re: calculate number of template instantiations Ruslan Mullakhmetov <tiabaldu@gmail.com> - 2011-10-25 20:05 +0400
      Re: calculate number of template instantiations Arne Mertz <arnemertz@googlemail.com> - 2011-10-26 02:10 -0700
    Re: calculate number of template instantiations Ruslan Mullakhmetov <tiabaldu@gmail.com> - 2011-10-25 19:42 +0400
      Re: calculate number of template instantiations Noah Roberts <roberts.noah@gmail.com> - 2011-10-25 09:43 -0700
        Re: calculate number of template instantiations Ruslan Mullakhmetov <tiabaldu@gmail.com> - 2011-10-25 20:46 +0400

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