2 variable "nested" loop with TMP

[Robin Eidissen]

What I try to do is to iterate over two variables using template
metaprogramming . I've specialized it such that when it reaches the end
of a row ot starts on the next and when it reaches the last row it stops..
At least that's what I thought I did, but VC71 says "warning C4717:
'LOOP<0,1>::DO' : recursive on all control paths, function will cause
runtime stack overflow".
What's wrong?

Here's the code:
template<int M, int N>
class LOOP {
private:
template<int I, int J>
class INNER {
public:
static inline void DO() {
cout << "(" << I << "," << J << ") ";
LOOP<I+1, J>::DO();
}
};
template<int J>
class INNER<M, J> {
public:
static inline void DO() {
LOOP<0, J+1>::DO();
}
};
template<int I>
class INNER<I, N> {
public:
static inline void DO() {
}
};
public:
static inline void DO() {
INNER<0, 0>::DO();
}
};

[Robin Eidissen]

Robin Eidissen wrote:

What I try to do is to iterate over two variables using template
metaprogramming . I've specialized it such that when it reaches the end
of a row ot starts on the next and when it reaches the last row it stops..
At least that's what I thought I did, but VC71 says "warning C4717:
'LOOP<0,1>::DO' : recursive on all control paths, function will cause
runtime stack overflow".
What's wrong?

Here's the code:
template<int M, int N>
class LOOP {
private:
template<int I, int J>
class INNER {
public:
static inline void DO() {
cout << "(" << I << "," << J << ") ";
LOOP<I+1, J>::DO();
}
};
template<int J>
class INNER<M, J> {
public:
static inline void DO() {
LOOP<0, J+1>::DO();
}
};
template<int I>
class INNER<I, N> {
public:
static inline void DO() {
}
};
public:
static inline void DO() {
INNER<0, 0>::DO();
}
};

Oh my god what a horrible mistake! I call LOOP again instead of INNER!

[Robin Eidissen]

But it still won't work correctly.
On "LOOP<3, 3>::DO();" it outputs "(0,1) (0,2) (1,2)" which is decidedly
wrong. It seems that the specializations aren't invoked at the right times.

[Victor Bazarov]

Robin Eidissen wrote:

But it still won't work correctly.
On "LOOP<3, 3>::DO();" it outputs "(0,1) (0,2) (1,2)" which is decidedly
wrong. It seems that the specializations aren't invoked at the right times.

Make sure you're using the right compiler for the job. VC++ v6 is
not up to snuff when it comes to templates.

V

[Robin Eidissen]

Victor Bazarov wrote:

Robin Eidissen wrote:

But it still won't work correctly.
On "LOOP<3, 3>::DO();" it outputs "(0,1) (0,2) (1,2)" which is
decidedly wrong. It seems that the specializations aren't invoked at
the right times.

Make sure you're using the right compiler for the job. VC++ v6 is
not up to snuff when it comes to templates.

V

I use Visual C++ 2003.

[Rob Williscroft]

Robin Eidissen wrote in news:c8******** **@orkan.itea.n tnu.no in
comp.lang.c++:

What I try to do is to iterate over two variables using template
metaprogramming . I've specialized it such that when it reaches the end
of a row ot starts on the next and when it reaches the last row it
stops.. At least that's what I thought I did, but VC71 says "warning
C4717: 'LOOP<0,1>::DO' : recursive on all control paths, function will
cause runtime stack overflow".
What's wrong?

Here's the code:
template<int M, int N>
class LOOP { public:
static inline void DO() {
inline here is unnessacery function's defined inside a class
are always inline.
};

With some correction's I got your version to work with an EDG compiler
but I couldn't be bothered wating for VC 7.1 to run out of memory,
g++ (3.4), didn't compile it either.

This seems to work though:

#include <iostream>
#include <ostream>

template< int M, int N, int I = M, int J = N >
struct loop
{
template < typename F >
static void apply( F f )
{
f( M - I, N - J );
loop<M, N, I, J - 1>::apply( f );
}
};

template< int M, int N, int I >
struct loop< M, N, I, 0 >
{
template < typename F >
static void apply( F f )
{
loop<M, N, I - 1, N>::apply( f );
}
};

template< int M, int N, int J >
struct loop< M, N, 0, J >
{
template < typename F >
static void apply( F )
{
}
};
void function( int i, int j )
{
std::cout << "(" << i << "," << j << ") ";
}

int main()
{
loop<3, 3>::apply( function );
}

HTH.

Rob.
--
http://www.victim-prime.dsl.pipex.com/

[Victor Bazarov]

Robin Eidissen wrote:

Victor Bazarov wrote:

Robin Eidissen wrote:

But it still won't work correctly.
On "LOOP<3, 3>::DO();" it outputs "(0,1) (0,2) (1,2)" which is
decidedly wrong. It seems that the specializations aren't invoked at
the right times.

Make sure you're using the right compiler for the job. VC++ v6 is
not up to snuff when it comes to templates.

V

I use Visual C++ 2003.

Please post the final code that you have, describe the output you get
and the output you would like to get. Otherwise, I am lost trying to
merge your original (apparently incorrect) code and the corrections
you described in replies to yourself.

Thanks.

V

[Robin Eidissen]

#include <iostream>
using namespace std;

template<int M, int N>
class LOOP {
private:
template<int I, int J>
class INNER {
public:
static inline void DO() {
cout << "(" << I << "," << J << ") ";
INNER<I+1, J>::DO();
}
};
template<int J>
class INNER<M, J> {
public:
static inline void DO() {
INNER<0, J+1>::DO();
}
};
template<>
class INNER<0, N> {
public:
static inline void DO() {
}
};
public:
static inline void DO() {
INNER<0, 0>::DO();
}
};

int main() {
LOOP<3, 3>::DO();
return 0;
}

I want this to output "(0,0) (1,0) (2,0) (0,1) (1,1) (2,1) (0,2) (1,2)
(2,2)". What is does output is: "(0,1) (0,2) (1,2)".

[Robin Eidissen]

Thanks that worked very nicely! But for "educationa l purposes" I'd
appreciate it if anyone can help me out with finding the error in the
latest version I posted.

[Robin Eidissen]

By the way, if I put "inline" in front of the "function" declaration,
will the entire thing be neatly unrolled with no function calls?