Hi,
after reading the article " The Standard Librarian : Defining Iterators
and Const Iterators" from Matt Austern: http://www.ddj.com/showArticle.jhtml...leID=184401331
I wanted to test using the non-template function friends of template
classes. So I devised this code:
===8<======8<== ====8<======8<= =====8<======8< ======8<===
#include <iostream>
using namespace std;
template <class T>
struct S
{
friend S foo( const S& s1, const S& s2 )
{
return S( s1.s + s2.s );
}
friend T operator+( const T& a, const S& s )
{
return a+s.s;
}
friend ostream& operator<<( ostream& s, const S& o )
{
s << "S(" << o.s << ")";
return s;
}
S( T a ) : s( a ) {}
T s;
};
int main()
{
S<ints1( 1 );
S<S<int s2( 10 );
cout << foo( s1, s2 );
cout << endl;
return 0;
}
===8<======8<== ====8<======8<= =====8<======8< ======8<===
It does compile but segfaults at runtime O_o
Could someone explain to me what I did wrong ?
thanks,
Pierre 3 1482
Pierre Barbier de Reuille wrote:
Hi,
after reading the article " The Standard Librarian : Defining Iterators
and Const Iterators" from Matt Austern: http://www.ddj.com/showArticle.jhtml...leID=184401331
I wanted to test using the non-template function friends of template
classes. So I devised this code:
===8<======8<== ====8<======8<= =====8<======8< ======8<===
#include <iostream>
using namespace std;
template <class T>
struct S
{
friend S foo( const S& s1, const S& s2 )
{
return S( s1.s + s2.s );
}
friend T operator+( const T& a, const S& s )
{
Try adding the following two lines here:
cout << "[In operator+]";
cout.flush();
return a+s.s;
}
friend ostream& operator<<( ostream& s, const S& o )
{
s << "S(" << o.s << ")";
return s;
}
S( T a ) : s( a ) {}
T s;
};
int main()
{
S<ints1( 1 );
S<S<int s2( 10 );
cout << foo( s1, s2 );
cout << endl;
return 0;
}
===8<======8<== ====8<======8<= =====8<======8< ======8<===
It does compile but segfaults at runtime O_o
Could someone explain to me what I did wrong ?
Add the two lines I indicated above, then re-compile and run your
program. I think you'll see the problem pretty quickly.
By the way, your program won't compile on Comeau, so I suspect your use
of templates is not correct. (But that is NOT the cause of your
described problem.)
Best regards,
Tom
Thomas Tutone wrote:
Pierre Barbier de Reuille wrote:
>Hi,
after reading the article " The Standard Librarian : Defining Iterators and Const Iterators" from Matt Austern: http://www.ddj.com/showArticle.jhtml...leID=184401331
I wanted to test using the non-template function friends of template classes. So I devised this code:
[...]
>> It does compile but segfaults at runtime O_o Could someone explain to me what I did wrong ?
Add the two lines I indicated above, then re-compile and run your
program. I think you'll see the problem pretty quickly.
By the way, your program won't compile on Comeau, so I suspect your use
of templates is not correct. (But that is NOT the cause of your
described problem.)
Best regards,
Tom
Thank you very much, I corrected the mistake ... Here is the code which
is working (I put only the class definition):
template <class T>
struct S
{
friend S foo( const S& s1, const S& s2 )
{
return S( s1.s + s2.s );
}
friend T operator+( const S& a, const T& s )
{
return a+s.s;
}
friend T operator+( const S& s1, const S& s2 )
{
return s1.s + s2.s;
}
friend ostream& operator<<( ostream& s, const S& o )
{
s << "S(" << o.s << ")";
return s;
}
S( T a ) : s( a ) {}
T s;
};
As for the correctness, I think it *is* correct. At least, the use of
the non-template friend functions is even explicitly allowed by the norm
(cf. the article which even gives the precise § in the norm).
However, if you could give me the error, I would be very interested.
Thanks,
Pierre
Pierre Barbier de Reuille wrote:
Thank you very much, I corrected the mistake ... Here is the code which
is working (I put only the class definition):
template <class T>
struct S
{
friend S foo( const S& s1, const S& s2 )
{
return S( s1.s + s2.s );
}
friend T operator+( const S& a, const T& s )
{
return a+s.s;
}
friend T operator+( const S& s1, const S& s2 )
{
return s1.s + s2.s;
}
friend ostream& operator<<( ostream& s, const S& o )
{
s << "S(" << o.s << ")";
return s;
}
S( T a ) : s( a ) {}
T s;
};
As for the correctness, I think it *is* correct. At least, the use of
the non-template friend functions is even explicitly allowed by the norm
(cf. the article which even gives the precise § in the norm).
However, if you could give me the error, I would be very interested.
Your code, as revised, compiles on Comeau without error. However, your
original code did not - see for yourself: http://www.comeaucomputing.com/tryitout/
"ComeauTest .c", line 14: error: no operator "+" matches these
operands
operand types are: const S<int+ const S<int>
return S( s1.s + s2.s );
^
detected during instantiation of class "S<T[with
T=S<int>]" at
line 45
1 error detected in the compilation of "ComeauTest .c".
As I said, you've now corrected the problem.
Best regards,
Tom This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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