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Hi template specialists,

I have a problem with the code listed below.

What I wanted to do is defining an operator<< that is able to output
a 'matrix<ELEMENT_T, INDEX_T>::subrange' object
into a 'std::basic_ostream<charT, traits>'.

For some reason, it does not work. The compiler always complains:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
te.cpp:
Error E2094 test.cpp: 'operator<<' not implemented in type
'std:stream' for arguments of type 'matrix<double,unsigned
int>::subrange' in function main(int,char * *)
*** 1 errors in Compile ***

The INTEL compiler gives a similar error.

On the other hand, MSVC 7 compiles without any warnings.

So - which of the compilers are correct?

And does anyone have an idea what there might be wrong with the code?

Note:

If I change the code to output a
'matrix<ELEMENT_T, INDEX_T>'
instead of a
'matrix<ELEMENT_T, INDEX_T>::subrange'
then it works perfectly for all compilers!

Only that this is not what I actually want to do.

So, please help me if you possibly can!

---------snip-----------
#include <iostream>
#include <cstdlib>


template<typename ELEMENT_T, typename INDEX_T>
struct matrix {
// I want to output an object of this nested type.
struct subrange {};
};

// This templated global function will not be used
// due to some reason unknown to me.
template<
typename ELEMENT_T, typename INDEX_T, typename charT, typename traits
>
std::basic_ostream<charT, traits> &operator<<(
std::basic_ostream<charT, traits> &os,
matrix<ELEMENT_T, INDEX_T>::subrange const &range)
{
os <<"matrix range";
return os;
}

int main(int, char **) {
matrix<double, size_t>::subrange x;
std::cout << x;
return EXIT_SUCCESS;
}
---------snip-----------

sincerly,

Guenther

Guenther Brunthaler wrote:
> std::basic_ostream<charT, traits> &operator<<(
> std::basic_ostream<charT, traits> &os,
> matrix<ELEMENT_T, INDEX_T>::subrange const &range)

typename matrix<ELEMENT_T, INDEX_T>::subrange const &range)

http://www.cuj.com/documents/s=8464/cuj0308dewhurst/

--
Attila aka WW

On Tue, 30 Sep 2003 10:03:42 GMT, Guenther Brunthaler
<> wrote:

>Hi template specialists,
>
>I have a problem with the code listed below.
>
>What I wanted to do is defining an operator<< that is able to output
>a 'matrix<ELEMENT_T, INDEX_T>::subrange' object
>into a 'std::basic_ostream<charT, traits>'.
>
>For some reason, it does not work. The compiler always complains:
>
>Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
>te.cpp:
>Error E2094 test.cpp: 'operator<<' not implemented in type
>'std:stream' for arguments of type 'matrix<double,unsigned
>int>::subrange' in function main(int,char * *)
>*** 1 errors in Compile ***
>
>The INTEL compiler gives a similar error.
>
>On the other hand, MSVC 7 compiles without any warnings.
>
>So - which of the compilers are correct?

INTEL and Borland. matrix<ELEMENT_T, INDEX_T>::subrange is a
nondeduced context since it requires template argument deduction of
the template parameters of a parent type based on the type of a nested
type. The compiler can't perform this deduction in general, because
the mapping of subtype onto template parameter types is not in general
many to one, but many to many.

>And does anyone have an idea what there might be wrong with the code?
>
>Note:
>
>If I change the code to output a
>'matrix<ELEMENT_T, INDEX_T>'
>instead of a
>'matrix<ELEMENT_T, INDEX_T>::subrange'
>then it works perfectly for all compilers!

Right, since that doesn't require argument deduction from a nested
type.

>Only that this is not what I actually want to do.
>
>So, please help me if you possibly can!

This version works:

#include <iostream>
#include <cstdlib>

template<typename ELEMENT_T, typename INDEX_T>
struct matrix {
// I want to output an object of this nested type.
struct subrange
{
template<typename charT, typename traits>
friend std::basic_ostream<charT, traits> &operator<<(
std::basic_ostream<charT, traits> &os,
subrange const &range)
{
os <<"matrix range";
return os;
}
};
};

int main(int, char **) {
matrix<double, size_t>::subrange x;
std::cout << x;
return EXIT_SUCCESS;
}

http://www.parashift.com/c++-faq-lit...html#faq-34.15
is the inverse of what I've done above - the linker errors have been
avoided by putting the definition inline. The template argument
deduction problem has been avoided by making removing the ELEMENT_T
and INDEX_T template parameters from operator<< so that it doesn't
have to deduce them.

When matrix<double, size_t>::subrange is instantiated, the friend
function will also be injected into the global namespace, hence koenig
lookup on the operator<< call finds the template and instantiates and
calls it for <char, char_traits<char> >.

Tom

Thanks a lot, Tom and Attila!

tom_usenet wrote:

> This version works:

But unfortunately not for C++ Builder. Nor for MSVC. Nor GCC.

But at least it works for INTEL.

Nevertheless, thanks to you now I know at least what the problem was!

The fact that so many C++ Compiler still do not comply with the C++
standard is a different story anyway


sincerly,

Guenther

(Note: If you want to reply via e-mail, please remove the
substrings "nospam_" and "_dontspam" from my address.)

On Wed, 01 Oct 2003 03:57:08 GMT, Guenther Brunthaler
<> wrote:

>Thanks a lot, Tom and Attila!
>
>tom_usenet wrote:
>
>> This version works:
>
>But unfortunately not for C++ Builder. Nor for MSVC. Nor GCC.
>
>But at least it works for INTEL.
>
>Nevertheless, thanks to you now I know at least what the problem was!
>
>The fact that so many C++ Compiler still do not comply with the C++
>standard is a different story anyway

GCC 3.2 is fine with it, as is MSVC7.1 (2003). Time to upgrade!

Tom