MESSAGE
| DATE | 2011-05-26 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [ruben@mrbrklyn.com: Re: [NYLXS - HANGOUT] C++ Workshop - New
|
----- Forwarded message from Ruben Safir -----
Date: Wed, 25 May 2011 17:16:18 -0400
From: Ruben Safir
To: Ruben Safir
Cc: nylug-talk-at-nylug.org
Subject: Re: [NYLXS - HANGOUT] C++ Workshop - New Webservices with OKWS -
Tuesday Night
User-Agent: Mutt/1.5.20 (2009-06-14)
On Wed, May 25, 2011 at 05:10:40PM -0400, Ruben Safir wrote:
> n Monday 23 May 2011 16:37:36 Ruben Safir wrote:
> > I'm having trouble understanding why my program is making a change in
> > the argument type of my template class function
> >
> > template < class T >
> > void List::find_value(T val)
>
> ...
> > I then pass int search_val to method
> > chainlist::List::find_value(T)
> > where T = stats::Distribution (where T is an int) on this line:
> >
> > dump->find_value(search_val);
> >
> > and that's where the weirdness happens. I have a type mismatch
> > since
> > I'm sending by value an integer instead of a stats::Distribution
>
> < Out of curiosity, is this typcastable? e.g.:
>
> dump->find_value((stats::Distribution)search_val);>
>
> That is exactly the type that the function takes in the context of the
> calling, class. T is an int. The issue winds up being that of
> implicit conversion which happens if there is a stats::Distirbution
> single argument constructor. For this to happen, the Template argument
> needs to be specifically defined, which it is in this case since it was
> defined in the class.
>
>
>
> << [function for reference: void List::find_value(T val) ]
>
> I think this is a case where the compiler needs help, because
> find_value() is
> looking for a templated generic value, so the compiler doesn't
> know that it
> can't send in a simple integer. The whole purpose of using
> templates is to
> keep the type abstract, so I'm not sure how you'd solve this
> within the
> function header. >>
>
> As it turns out, this is an explicit rule. If T is not defined, the
> implicit conversion can not happen a`nd it is considered, "Can not be
> deduced".
>
> o
>
>
> <<
> I've been trying to read your C++ code, but I've been finding
> it difficult;
> the stream of templated objects... wow. However in the middle
> of trying to
> read things that I can parse, I noticed the following:
> >>
>
> Well, it's an excersize in templates. Your familiar with the rules for
> vector<> and list<> because they are part of the standard template
> libray. My chainlist::List seems to be pretty decent at this point, but
> the syntax is unknown unless you pour over the code *List<>->cursor()
> returns a chainlist::Node class object. It contains a pointer to a
> value of type T and a pointer to the Next Node
>
> Things get exciting when T is its own class.
>
> << float mean_list( )
> ...
> while(tallies->cursor() != tallies->endd() ){
> ...
> if(dump->cursor() != NULL)
> ...
> }
> ...
> if(dump->cursor() != 0)
>
> If dump->cursor() is a pointer, then compare it with NULL, not 0.
> >>
>
> There is a lot of debate on this issue. Strausoup strongly urges 0,
> but frankly, dealing with nulls in C++ is a PIA, and even moreso now
> with the new standard which blows a warning at you if you assign NULL
> to an int type variable.
>
> << Even if
> this works, I'd choose one test and try to stick to it for
> readability
> reasons.
> >>
>
> Ruben
>
>
> -- Chris
>
> --
> Chris Knadle
> Chris.Knadle at coredump.us
>
>
From usenet
I'm getting this warning that appears in the 4.6 GCC compiler that
didn't
happen before.
the warning is
/home/ruben/cplus/link_list_template_mysql/stats.h|45 col 42| warning:
converting to non-pointer type .int. from NULL [-Wconversion-null]
if comes from a default constructor
Distribution():freq(NULL), occurances(0){};
occurances is an int type, and the compiler is complaining about
occurances(0)
it goes away when I change it to
Distribution():freq(NULL){
occurances = 0;
};
but then it complains about freq which is of type T in a template
Ruben
>
> --
> http://www.mrbrklyn.com - Interesting Stuff
> http://www.nylxs.com - Leadership Development in Free Software
>
> So many immigrant groups have swept through our town that Brooklyn, like Atlantis, reaches mythological proportions in the mind of the world - RI Safir 1998
>
> http://fairuse.nylxs.com DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
>
> "Yeah - I write Free Software...so SUE ME"
>
> "The tremendous problem we face is that we are becoming sharecroppers to our own cultural heritage -- we need the ability to participate in our own society."
>
> "> I'm an engineer. I choose the best tool for the job, politics be damned.<
> You must be a stupid engineer then, because politcs and technology have been attached at the hip since the 1st dynasty in Ancient Egypt. I guess you missed that one."
>
> ? Copyright for the Digital Millennium
--
http://www.mrbrklyn.com - Interesting Stuff
http://www.nylxs.com - Leadership Development in Free Software
So many immigrant groups have swept through our town that Brooklyn, like Atlantis, reaches mythological proportions in the mind of the world - RI Safir 1998
http://fairuse.nylxs.com DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
"Yeah - I write Free Software...so SUE ME"
"The tremendous problem we face is that we are becoming sharecroppers to our own cultural heritage -- we need the ability to participate in our own society."
"> I'm an engineer. I choose the best tool for the job, politics be damned.<
You must be a stupid engineer then, because politcs and technology have been attached at the hip since the 1st dynasty in Ancient Egypt. I guess you missed that one."
? Copyright for the Digital Millennium
----- End forwarded message -----
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