template function as function parameter

[rg]

Hi all,

I was wondering if anyone had dealt with a similar problem. I need to use a
template function as the parameter for a particular function (also template
function).
The program compiles into an object file but then at the final stage it says
that it can't find template function. The platform is WindowsXP Pro, MSCV++
..Net.

More specifically what I want to do is write an atl algorithm that will also
accept another algorithm as a function parameter. This is inteface of the
outer algorithm:

template <class iterator, class outiterator, class Alg>
void transform_slide ( iterator begin, iterator end, outiterator
outbegin, std::size_t slide, Alg alg)
{
std::size_t loop = std::distance( begin, end) / slide;
for ( std::size_t x = 0; x < loop; ++x, ++outbegin, begin =
std::advance( begin, size) ) // only do complete cycles, not parts
*outbegin = alg( begin, std::advance( begin, size) );
}

What I want to do with is perform some calculations on range on a sliding
basis. For example, if I have a array of 1000 values, I may want to
calculate the average of every 100 of those values.

Any help would be appreciated. Many Thanks in advance.

RG

[David Hilsee]

Re: template function as function parameter


"rg" <rg1117@hotmail .com> wrote in message
news:cep3ld$f85 $1@news.freedom 2surf.net...[color=blue]
> Hi all,
>
> I was wondering if anyone had dealt with a similar problem. I need to use[/color]
a[color=blue]
> template function as the parameter for a particular function (also[/color]
template[color=blue]
> function).
> The program compiles into an object file but then at the final stage it[/color]
says[color=blue]
> that it can't find template function. The platform is WindowsXP Pro,[/color]
MSCV++[color=blue]
> .Net.[/color]

Are you falling into the trap where you place template code in the
implementation (.cpp) file instead of placing all of it in the header? See
the FAQ
(http://www.parashift.com/c++-faq-lit...templates.html) for
info about linker errors with templates.
[color=blue]
> More specifically what I want to do is write an atl algorithm that will[/color]
also[color=blue]
> accept another algorithm as a function parameter. This is inteface of the
> outer algorithm:
>
> template <class iterator, class outiterator, class Alg>
> void transform_slide ( iterator begin, iterator end, outiterator
> outbegin, std::size_t slide, Alg alg)
> {
> std::size_t loop = std::distance( begin, end) / slide;
> for ( std::size_t x = 0; x < loop; ++x, ++outbegin, begin =
> std::advance( begin, size) ) // only do complete cycles, not parts
> *outbegin = alg( begin, std::advance( begin, size) );
> }[/color]

This may have weird behavior on some inputs. Consider the behavior if the
distance is 1 and the slide is 2, where nothing is performed. Also, you
could accidentally run off the end of the container with the call to
advance(). Maybe something like this would be safer:

template <class iterator, class outiterator, class Alg>
void transform_slide ( iterator begin, iterator end, outiterator
outbegin, std::size_t slide, Alg alg)
{
std::size_t dist = std::distance( begin, end );
for ( std::size_t x = 0; x < dist; x += slide, ++outbegin )
// only do complete cycles, not parts
iterator tmp = std::advance( begin, std::min(slide, dist-x) );
*outbegin = alg( begin, tmp );
begin = tmp;
}

The code above is untested.

--
David Hilsee

[David Hilsee]

Re: template function as function parameter

"David Hilsee" <davidhilseenew s@yahoo.com> wrote in message
news:-8ydnZJla9M6tY3c RVn-uA@comcast.com. ..
[color=blue]
> This may have weird behavior on some inputs. Consider the behavior if the
> distance is 1 and the slide is 2, where nothing is performed. Also, you
> could accidentally run off the end of the container with the call to
> advance(). Maybe something like this would be safer:[/color]

Sorry, that comment about the end of the container, AFAICT, does not apply
to your code. It applies to the code that I provided if the call to
std::min is removed.

--
David Hilsee

[David Hilsee]

Re: template function as function parameter

"David Hilsee" <davidhilseenew s@yahoo.com> wrote in message
news:-8ydnZJla9M6tY3c RVn-uA@comcast.com. ..
[color=blue]
> template <class iterator, class outiterator, class Alg>
> void transform_slide ( iterator begin, iterator end, outiterator
> outbegin, std::size_t slide, Alg alg)
> {
> std::size_t dist = std::distance( begin, end );
> for ( std::size_t x = 0; x < dist; x += slide, ++outbegin )
> // only do complete cycles, not parts
> iterator tmp = std::advance( begin, std::min(slide, dist-x) );
> *outbegin = alg( begin, tmp );
> begin = tmp;
> }[/color]

And for my final response to myself, I would like to point out that I didn't
even try to understand the comment that I cut-and-pasted from the original
code and made the code I posted almost completely irrelevant. *smacks
forehead*

--
David Hilsee

[John Harrison]

Re: template function as function parameter

On Tue, 3 Aug 2004 23:28:34 +0100, rg <rg1117@hotmail .com> wrote:
[color=blue]
> Hi all,
>
> I was wondering if anyone had dealt with a similar problem. I need to
> use a
> template function as the parameter for a particular function (also
> template
> function).
> The program compiles into an object file but then at the final stage it
> says
> that it can't find template function. The platform is WindowsXP Pro,
> MSCV++
> .Net.
>
> More specifically what I want to do is write an atl algorithm that will
> also
> accept another algorithm as a function parameter. This is inteface of the
> outer algorithm:
>
> template <class iterator, class outiterator, class Alg>
> void transform_slide ( iterator begin, iterator end, outiterator
> outbegin, std::size_t slide, Alg alg)
> {
> std::size_t loop = std::distance( begin, end) / slide;
> for ( std::size_t x = 0; x < loop; ++x, ++outbegin, begin =
> std::advance( begin, size) ) // only do complete cycles, not parts
> *outbegin = alg( begin, std::advance( begin, size) );
> }
>
> What I want to do with is perform some calculations on range on a sliding
> basis. For example, if I have a array of 1000 values, I may want to
> calculate the average of every 100 of those values.
>
> Any help would be appreciated. Many Thanks in advance.
>
> RG
>[/color]

I think I'd want to see the code that calls transform_slide .

Maybe I've having a bad day but I can't see how a template function (or
any sort of function) could be a suitable argument for class Arg, surely
you need a non-type template argument? Something like

template <class I, class OI, class T>
void transform_slide (I begin, I end, OI outbegin, size_t slide, T
(*Alg)(I, size_t))
{
}

john

[John Harrison]

Re: template function as function parameter

On Wed, 04 Aug 2004 06:50:46 +0100, John Harrison
<john_andronicu s@hotmail.com> wrote:
[color=blue]
>
> Maybe I've having a bad day but I can't see how a template function (or
> any sort of function) could be a suitable argument for class Arg, surely
> you need a non-type template argument?[/color]

Yeah I've having a bad day, please ignore.

john

[rg]

Re: template function as function parameter

Hi,
Thanks for your reply.
The algorithm that I am talking about is indeed in the header (.hpp) file. I
think the problem is that the template function is not actually instantiated
until it is used so when I send a pointer to it, there is nothing to point
at. I'm wondering if there's anything to deal with that. I tried:

using alg< vector<int>::it erator >;

but that didn't work.

Many thanks

RG

"David Hilsee" <davidhilseenew s@yahoo.com> wrote in message
news:-8ydnZJla9M6tY3c RVn-uA@comcast.com. ..[color=blue]
>
> "rg" <rg1117@hotmail .com> wrote in message
> news:cep3ld$f85 $1@news.freedom 2surf.net...[color=green]
> > Hi all,
> >
> > I was wondering if anyone had dealt with a similar problem. I need to[/color][/color]
use[color=blue]
> a[color=green]
> > template function as the parameter for a particular function (also[/color]
> template[color=green]
> > function).
> > The program compiles into an object file but then at the final stage it[/color]
> says[color=green]
> > that it can't find template function. The platform is WindowsXP Pro,[/color]
> MSCV++[color=green]
> > .Net.[/color]
>
> Are you falling into the trap where you place template code in the
> implementation (.cpp) file instead of placing all of it in the header?[/color]
See[color=blue]
> the FAQ
> (http://www.parashift.com/c++-faq-lit...templates.html) for
> info about linker errors with templates.
>[color=green]
> > More specifically what I want to do is write an atl algorithm that will[/color]
> also[color=green]
> > accept another algorithm as a function parameter. This is inteface of[/color][/color]
the[color=blue][color=green]
> > outer algorithm:
> >
> > template <class iterator, class outiterator, class Alg>
> > void transform_slide ( iterator begin, iterator end, outiterator
> > outbegin, std::size_t slide, Alg alg)
> > {
> > std::size_t loop = std::distance( begin, end) / slide;
> > for ( std::size_t x = 0; x < loop; ++x, ++outbegin, begin =
> > std::advance( begin, size) ) // only do complete cycles, not parts
> > *outbegin = alg( begin, std::advance( begin, size) );
> > }[/color]
>
> This may have weird behavior on some inputs. Consider the behavior if the
> distance is 1 and the slide is 2, where nothing is performed. Also, you
> could accidentally run off the end of the container with the call to
> advance(). Maybe something like this would be safer:
>
> template <class iterator, class outiterator, class Alg>
> void transform_slide ( iterator begin, iterator end, outiterator
> outbegin, std::size_t slide, Alg alg)
> {
> std::size_t dist = std::distance( begin, end );
> for ( std::size_t x = 0; x < dist; x += slide, ++outbegin )
> // only do complete cycles, not parts
> iterator tmp = std::advance( begin, std::min(slide, dist-x) );
> *outbegin = alg( begin, tmp );
> begin = tmp;
> }
>
> The code above is untested.
>
> --
> David Hilsee
>
>[/color]

[rg]

Re: template function as function parameter

Hi,

Thank you for your reply.

I was going to use it to calculate the rms power for each second in a sound
sample. Currently I'm using a rms_slide algorithm but I wanted to make a
more generic algorithm that can be used for sliding against any custom
algorithm.

Many Thanks

RG

"John Harrison" <john_andronicu s@hotmail.com> wrote in message
news:opsb606wa5 212331@andronic us...[color=blue]
> On Tue, 3 Aug 2004 23:28:34 +0100, rg <rg1117@hotmail .com> wrote:
>[color=green]
> > Hi all,
> >
> > I was wondering if anyone had dealt with a similar problem. I need to
> > use a
> > template function as the parameter for a particular function (also
> > template
> > function).
> > The program compiles into an object file but then at the final stage it
> > says
> > that it can't find template function. The platform is WindowsXP Pro,
> > MSCV++
> > .Net.
> >
> > More specifically what I want to do is write an atl algorithm that will
> > also
> > accept another algorithm as a function parameter. This is inteface of[/color][/color]
the[color=blue][color=green]
> > outer algorithm:
> >
> > template <class iterator, class outiterator, class Alg>
> > void transform_slide ( iterator begin, iterator end, outiterator
> > outbegin, std::size_t slide, Alg alg)
> > {
> > std::size_t loop = std::distance( begin, end) / slide;
> > for ( std::size_t x = 0; x < loop; ++x, ++outbegin, begin =
> > std::advance( begin, size) ) // only do complete cycles, not parts
> > *outbegin = alg( begin, std::advance( begin, size) );
> > }
> >
> > What I want to do with is perform some calculations on range on a[/color][/color]
sliding[color=blue][color=green]
> > basis. For example, if I have a array of 1000 values, I may want to
> > calculate the average of every 100 of those values.
> >
> > Any help would be appreciated. Many Thanks in advance.
> >
> > RG
> >[/color]
>
> I think I'd want to see the code that calls transform_slide .
>
> Maybe I've having a bad day but I can't see how a template function (or
> any sort of function) could be a suitable argument for class Arg, surely[/color]
[color=blue]
> you need a non-type template argument? Something like
>
> template <class I, class OI, class T>
> void transform_slide (I begin, I end, OI outbegin, size_t slide, T
> (*Alg)(I, size_t))
> {
> }
>
> john[/color]

[David Hilsee]

Re: template function as function parameter

"rg" <rg1117@hotmail .com> wrote in message
news:ceqam2$r01 $1@news.freedom 2surf.net...

I think you might have overlooked John's request:
[color=blue][color=green]
> > I think I'd want to see the code that calls transform_slide .[/color][/color]

Also, it might be good to know exactly where the caller's code, and any code
it references, is located (defined in "blah.cpp"/declared in "blah.hpp") .

--
David Hilsee

[rg]

Re: template function as function parameter

Hi,

Sorry for not having replied earlier, been extremely busy. Here is the code:

file stats.hpp
{
#insert...
.....

template <class iterator>
double rms(iterator begin, iterator end) // calculates the Root Mean
Square Power for some range of values
{
return std::sqrt(
std::accumulate (
begin, end, 0.0, boost::bind<dou ble>(
std::plus<doubl e>(), _1,
boost::bind(std ::pow, _2, 2)
)
) / std::distance(b egin, end)
);
}

template <class iterator, class outiterator>
void rms_slide ( iterator begin, iterator end, outiterator outbegin,
std::size_t slide) // calculates RMS over a sliding frame
{
std::size_t loop = std::distance( begin, end) / slide;
end = begin + slide;
for (
std::size_t x = 0;
x < loop;
++x, ++outbegin, std::advance( begin, slide), std::advance (
end, slide)
) // only do complete cycles, not parts
*outbegin = rms( begin, end );
}

} // end stats.hpp


file main.cpp
{
short * wav = new short[SIZE]; //array contain audio data
std::vector<int > power; // to hold rms power information over time

rms_slide( wav, wav + SIZE, std::back_inser ter(power), SLIDE_SIZE );
// calculate RMS power for frames of size SLIDE_SIZE

delete[] wav;
}// end main.cpp


When I did this, I wondered whether I could develop a more generic version
of the slide algorithm which I described in my earlier post. Instead of
calling rms_slide, I would call:

transform_slide (
wav,
wav + SIZE,
std::back_inser ter(power),
SLIDE_SIZE,
rms
);

and tell it to apply the rms algorithm over the sliding frame and insert the
value into the output iterator.

Hope it makes sense. Many Thanks for your help.

RG

"David Hilsee" <davidhilseenew s@yahoo.com> wrote in message
news:dvSdncTBw8 sSGYzcRVn-qQ@comcast.com. ..[color=blue]
> "rg" <rg1117@hotmail .com> wrote in message
> news:ceqam2$r01 $1@news.freedom 2surf.net...
>
> I think you might have overlooked John's request:
>[color=green][color=darkred]
> > > I think I'd want to see the code that calls transform_slide .[/color][/color]
>
> Also, it might be good to know exactly where the caller's code, and any[/color]
code[color=blue]
> it references, is located (defined in "blah.cpp"/declared in "blah.hpp") .
>
> --
> David Hilsee
>
>[/color]

[David Hilsee]

Re: template function as function parameter

"rg" <rg1117@hotmail .com> wrote in message
news:cf822j$4ig $1@news.freedom 2surf.net...[color=blue]
> Hi,
>
> Sorry for not having replied earlier, been extremely busy. Here is the[/color]
code:[color=blue]
>
> file stats.hpp
> {
> #insert...
> ....
>
> template <class iterator>
> double rms(iterator begin, iterator end) // calculates the Root[/color]
Mean[color=blue]
> Square Power for some range of values
> {
> return std::sqrt(
> std::accumulate (
> begin, end, 0.0, boost::bind<dou ble>(
> std::plus<doubl e>(), _1,
> boost::bind(std ::pow, _2, 2)
> )
> ) / std::distance(b egin, end)
> );
> }
>
> template <class iterator, class outiterator>
> void rms_slide ( iterator begin, iterator end, outiterator outbegin,
> std::size_t slide) // calculates RMS over a sliding frame
> {
> std::size_t loop = std::distance( begin, end) / slide;
> end = begin + slide;
> for (
> std::size_t x = 0;
> x < loop;
> ++x, ++outbegin, std::advance( begin, slide), std::advance (
> end, slide)
> ) // only do complete cycles, not parts
> *outbegin = rms( begin, end );
> }
>
> } // end stats.hpp
>
>
> file main.cpp
> {
> short * wav = new short[SIZE]; //array contain audio data
> std::vector<int > power; // to hold rms power information over time
>
> rms_slide( wav, wav + SIZE, std::back_inser ter(power),[/color]
SLIDE_SIZE );[color=blue]
> // calculate RMS power for frames of size SLIDE_SIZE
>
> delete[] wav;
> }// end main.cpp
>
>
> When I did this, I wondered whether I could develop a more generic version
> of the slide algorithm which I described in my earlier post. Instead of
> calling rms_slide, I would call:
>
> transform_slide (
> wav,
> wav + SIZE,
> std::back_inser ter(power),
> SLIDE_SIZE,
> rms
> );
>
> and tell it to apply the rms algorithm over the sliding frame and insert[/color]
the[color=blue]
> value into the output iterator.
>
> Hope it makes sense. Many Thanks for your help.[/color]

How about:

template <class iterator, class outiterator, class fun>
void transform_slide ( iterator begin, iterator end, outiterator
outbegin,
std::size_t slide, fun f )
{
std::cout << "A" << std::endl;
std::size_t loop = std::distance( begin, end ) / slide;
end = begin;
std::advance( end, slide );
for (
std::size_t x = 0;
x < loop;
++x, ++outbegin, begin = end, std::advance(en d,slide)
)

*outbegin = f( begin, end );
}

template <class it>
double rms(it beg, it end) {return 0;}

// Allows the compiler to figure out what type the iterator
// should be
struct rms_wrapper {
template <class it>
double operator()(it beg, it end){
return rms(beg,end);
}
};

int main() {
std::vector<dou ble> v;

transform_slide (v.begin(),v.en d(),v.begin(),1 ,rms<std::vecto r<double>::iter a
tor>);
transform_slide (v.begin(),v.en d(),v.begin(),1 ,rms_wrapper()) ;
}

But didn't you say something about a linker error? Can't find the function,
or something to that effect?

--
David Hilsee