new way of overloading operators in templates??

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June 29th, 2006, 05:19 PM
Luis G

new way of overloading operators in templates??

First of all, this code does compile with g++ 3.3.5. But with g++ 4.0.2 it gives me a few errors. g++ enters the #else portion. The _MSC_VER is meant to be able to compile it in VC++ 5

Code:

#ifdef _MSC_VER friend CMatriz<TG> operator+(const TG &op1,const CMatriz<TG> op2); // objeto TG + CMatriz friend CMatriz<TG> operator+(const double &op1,const CMatriz<TG> &op2); // constante + CMatriz #else /*Next line is 64*/ friend CMatriz<TG> operator+ <>(const TG &op1,const CMatriz<TG> &op2); // objeto TG + CMatriz friend CMatriz<TG> operator+ <>(const double &op1,const CMatriz<TG> &op2); // constante + CMatriz #endif

The compiler says:
Matriz.h:64: error: declaration of 'operator+' as non-function
This error happens too with another operators. However with the <<:

Code:

#ifdef _MSC_VER friend ostream &operator<<(ostream &os,const CMatriz<TG> &op); #else /*Next line is 87*/ friend ostream &operator<< <>(ostream &os,const CMatriz<TG> &op); #endif

The compiler gives a different error:
Matriz.h:87: error: template-id 'operator<< <>' for std::basic_ostream<char, std::char_traits<char> >& operator<<(std::basic_ostream<char, std::char_traits<char> >&, const CMatriz<CComplejo>&)' does not match any template declaration

Any clues as to how should these be declared?
June 29th, 2006, 06:20 PM
Luis G

Re: new way of overloading operators in templates??

For the record, I solved the ostream << problem by adding:

Code:

template<class TG> class CMatriz; template<class TG> ostream& operator<< (ostream & os, const CMatriz<TG> &op);

Before declaring the template class. I haven't found the way to fix it for the other operators.
June 30th, 2006, 01:22 AM
Viorel

Re: new way of overloading operators in templates??

Maybe for friend declarations you should try this:

Code:

template< class W > friend CMatriz<W> operator+ (const W &op1,const CMatriz<W> &op2); // objeto W + CMatriz template< class W > friend CMatriz<W> operator+ (const double &op1, const CMatriz<W> &op2); // constante + CMatriz

I hope it helps.
June 30th, 2006, 03:18 AM
Graham

Re: new way of overloading operators in templates??

What are the empty angle brackets doing?
June 30th, 2006, 09:36 AM
TomWidmer

Re: new way of overloading operators in templates??

In order to use the <> versions, declarations of the templates in question have to be visible. So you need:

Code:

template<class TG> class CMatriz; template<class TG> ostream& operator<< (ostream & os, const CMatriz<TG> &op); template< class W > CMatriz<W> operator+ (const W &op1,const CMatriz<W> &op2); template< class W > CMatriz<W> operator+ (const double &op1, const CMatriz<W> &op2); template<class TG> class CMatriz { //friends, etc. };

Also, the friend declarations would be more explicit if you specified the template argument, rather than leaving it up to template argument deduction. e.g.

Code:

friend CMatriz<TG> operator+ <TG>(const double &op1,const CMatriz<TG> &op2);
June 30th, 2006, 09:38 AM
TomWidmer

Re: new way of overloading operators in templates??

Quote:

Originally Posted by Graham

What are the empty angle brackets doing?

If you don't have them, the compiler assumes that the friend declaraton refers to a non-template function from the surrounding namespace, so the template function that is supposed to be a friend isn't made one.
June 30th, 2006, 11:40 AM
Luis G

Re: new way of overloading operators in templates??

Many thanks for the help, I've done what you said but it still gives the same errors.

This is how it looks now:

Code:

template<class TG> class CMatriz; template<class TG> ostream& operator<< (ostream & os, const CMatriz<TG> &op); template<class TG> CMatriz<TG> operator+ (const TG &op1,const CMatriz<TG> &op2); // objeto TG + CMatriz template<class TG> CMatriz<TG> operator+ (const double &op1,const CMatriz<TG> &op2); // constante + CMatriz template<class TG> CMatriz<TG> operator* (const TG &op1,const CMatriz<TG> &op2); // Objeto TG por matriz template<class TG> CMatriz<TG> operator* (const double &op1,const CMatriz<TG> &op2); // Constante por matriz template<class TG> class CMatriz { public: CMatriz(unsigned int j=1,unsigned int k=1); CMatriz(const CMatriz<TG> &cpv); ~CMatriz(); // Other stuff here //....... below is line 74 friend CMatriz<TG> operator+ <>(const TG &op1,const CMatriz<TG> &op2); // objeto TG + CMatriz friend CMatriz<TG> operator+ <>(const double &op1,const CMatriz<TG> &op2); // constante + CMatriz //....... below is line 90 friend CMatriz<TG> operator* <>(const TG &op1,const CMatriz<TG> &op2); // Objeto TG por matriz friend CMatriz<TG> operator* <>(const double &op1,const CMatriz<TG> &op2); // Constante por matriz //....... protected: //....... } /** Other functions ..... */ template<class TG> CMatriz<TG> operator+(const TG &op1,const CMatriz<TG> &op2) { unsigned int j,k; CMatriz<TG> suma(op2.m_reng,op2.m_cols); for(j=0;j<op2.m_reng;j++) for(k=0;k<op2.m_cols;k++) suma.inserta(j,k,op2.obten(j,k)+op1); return suma; }

The errors reported:

Code:

legg@lc65:~/tempo$ make g++ -O -g -I. -DLinux -Wall -c main.cpp Matriz.h:74: error: declaration of 'operator+' as non-function Matriz.h:74: error: expected ';' before '<' token Matriz.h:75: error: declaration of 'operator+' as non-function Matriz.h:75: error: expected ';' before '<' token Matriz.h:90: error: declaration of 'operator*' as non-function Matriz.h:90: error: expected ';' before '<' token Matriz.h:91: error: declaration of 'operator*' as non-function Matriz.h:91: error: expected ';' before '<' token Matriz.h: In function 'CMatriz<TG> operator*(const double&, const CMatriz<TG>&) [with TG = int]': main.cpp:39: instantiated from here Matriz.h:102: error: 'unsigned int CMatriz<int>::m_reng' is protected Matriz.h:354: error: within this context Matriz.h:102: error: 'unsigned int CMatriz<int>::m_cols' is protected Matriz.h:354: error: within this context Matriz.h:102: error: 'unsigned int CMatriz<int>::m_reng' is protected Matriz.h:355: error: within this context Matriz.h:102: error: 'unsigned int CMatriz<int>::m_cols' is protected Matriz.h:356: error: within this context Matriz.h: In function 'CMatriz<TG> operator*(const double&, const CMatriz<TG>&) [with TG = CComplejo]': main.cpp:87: instantiated from here Matriz.h:102: error: 'unsigned int CMatriz<CComplejo>::m_reng' is protected Matriz.h:354: error: within this context Matriz.h:102: error: 'unsigned int CMatriz<CComplejo>::m_cols' is protected Matriz.h:354: error: within this context Matriz.h:102: error: 'unsigned int CMatriz<CComplejo>::m_reng' is protected Matriz.h:355: error: within this context Matriz.h:102: error: 'unsigned int CMatriz<CComplejo>::m_cols' is protected Matriz.h:356: error: within this context make: *** [main.o] Error 1

The protected errors are spurious (should be).

If I include a declaration like:

Code:

friend CMatriz<TG> operator* <TG>(const double &op1,const CMatriz<TG> &op2); // Constante por matriz

It won't compile under 3.3 either.
June 30th, 2006, 03:43 PM
Luis G

Re: new way of overloading operators in templates??

I found out. The correct code is:

Code:

#ifdef _MSC_VER friend CMatriz<TG> operator+(const TG &op1,const CMatriz<TG> &op2); // objeto TG + CMatriz friend CMatriz<TG> operator+(const double &op1,const CMatriz<TG> &op2); // constante + CMatriz #elif __GNUC__ > 3 || (__GNUC__==3 && __GNUC_MINOR__ >=4) friend CMatriz<TG> (::operator+ <TG>)(const TG &op1,const CMatriz<TG> &op2); // objeto TG + CMatriz friend CMatriz<TG> (::operator+ <TG>)(const double &op1,const CMatriz<TG> &op2); // constante + CMatriz #else friend CMatriz<TG> operator+ <>(const TG &op1,const CMatriz<TG> &op2); // objeto TG + CMatriz friend CMatriz<TG> operator+ <>(const double &op1,const CMatriz<TG> &op2); // constante + CMatriz #endif

The code I was after is the one meant for gcc>=3.4, that however won't compile in 3.3

Any idea as to what does the new code means? :confused:
July 3rd, 2006, 08:30 AM
NMTop40

Re: new way of overloading operators in templates??

Quote:

Originally Posted by Graham

What are the empty angle brackets doing?

Assuming we are referring to the same thing, I am sure you know why you use empty angle brackets in template friend specifications.

Code:

template < typename T > class Matriz; template < typename T > std::ostream & operator<< ( std::ostream &, const Matriz< T > & ); template < typename T > class Matriz { friend std::ostream & operator<< <> ( std::ostream &, const Matriz & ); // rest of template Matriz }; template < typename T > std::ostream & operator<< ( std::ostream & os, const Matriz<T> & mat ) { // implement here }

The angled brackets in friend declaration tell the compiler that it is a template function.
July 3rd, 2006, 09:29 AM
Graham

Re: new way of overloading operators in templates??

I was suggesting looking into the reason why they were there in one conditional section, but not in the other (unless it was down to compiler silliness - which seems probable, given mention of VC5).

Mind you, I rarely use friends, and I don't think I've ever coded a template friend...