template question.

template question.

[Satish]

Hi,

I have just started using the egcs-1.0.3 compiler.
I ran into a problem which works fine with SGI CC
compiler. Can you please point out how to make it
work.

Here is a sample that shows the problem..

I get these errors trying to compile the basic skeleton programs
shown below:
Undefined                       first referenced
 symbol                             in file
Foo<Bar *>::Foo(void)               /var/tmp/cc0wXca01.o
ld: fatal: Symbol referencing errors. No output written to tmp
collect2: ld returned 1 exit status

Also, the presence of def. for operator<< (comments removed)
causes the following error, where I expected it to work just fine..
Do I need to use -fguiding-decls?

In file included from main.C:2:
templ.h:12: warning: friend declaration `class ostream & operator
<<(class ostream &, const class Foo<T> &)'
templ.h:12: warning:   will not be treated as a template instantiation
templ.h:12: warning:   unless you compile with -fguiding-decls
templ.h:12: warning:   or add <> after the function name


The file listings are as follows:
main.C
-------
#include "templ.h"
#include "bar.h"

void main( void ){
  Foo<Bar*>* foo = new Foo<Bar*>();
}

templ.C
-------
#include "templ.h"

template <class T>
Foo<T>::Foo( void ) {
}

template <class T>
void Foo<T>::bar( T& t ) const {
}

/*
template <class T>
ostream& operator<<( ostream& os, const Foo<T>& t ) {
  return os;
}
*/

templ.h
-------
#ifndef TEMPL_H_
#define TEMPL_H_

#include <iostream.h>

template <class T>
class Foo {
public:
  Foo( void );
  void bar( T& t ) const;
  //friend ostream& operator<<( ostream&, const Foo<T>& );
};

#endif

Thanks,
Satish.

Re: template question.

[Alexandre Oliva]

Satish  <satish@dakotacom.net> writes:

> Foo<Bar *>::Foo(void)               /var/tmp/cc0wXca01.o

Templates must be defined in every translation unit in which they're
used, unless you explicitly instantiate them.

> Also, the presence of def. for operator<< (comments removed)
> causes the following error, where I expected it to work just fine..

Check http://egcs.cygnus.com/faq.html#friend

-- 
Alexandre Oliva
mailto:oliva@dcc.unicamp.br mailto:oliva@gnu.org mailto:aoliva@acm.org
http://www.dcc.unicamp.br/~oliva
Universidade Estadual de Campinas, SP, Brasil

Re: template question

[Alexander Sieb]

Zoltan Nagy wrote:
> 
> Hi,
> 
> I tried to compile the small code below using the g++-3.2.1 but I got
> the following error message:
> 
> test.cc: In member function `void C<TTT>::ff() [with TTT = double]':
> test.cc:31:   instantiated from here
> test.cc:20: no matching function for call to `A<double>::f(B<const
> double&, double>&, double&)'
> 
> Is it a bug in the compiler or I do something wrong?
> 


Seems like T1 is ambiguous. 

  template<class T1, class T2>
  void f(const B<T1,T2>&, T1){}
                 ^^       ^^
                 ||       ||
 const double& from b.   double from function call
                      ||
                      \/
              What should T1 really be?

In b you define what becomes T1 as const double& while in the member function call
the second parameter is double. T1 cannot be both at the same time.

-- 
Regards,
	Alexander

template question

[Zoltan Nagy]

Hi,

I tried to compile the small code below using the g++-3.2.1 but I got
the following error message:

test.cc: In member function `void C<TTT>::ff() [with TTT = double]':
test.cc:31:   instantiated from here
test.cc:20: no matching function for call to `A<double>::f(B<const
double&, double>&, double&)'

Is it a bug in the compiler or I do something wrong?

Cheers,
Zoltan


template<class T1, class T2>
struct B {
  typedef T2 res_type;
};

template<class TT>
struct A {
  template<class T1, class T2>
  void f(const B<T1,T2>&, T1){}
};


B<const double&, double> b;

template <class TTT>
struct C {
  void ff() {
    double x =12;
    a.f(b, x);
  }

  A<TTT> a;
};


int main()
{
  C<double> c;

  c.ff();

  return 0;
}