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Michael Hopkins
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 Posted: Sat Oct 29, 2005 1:10 pm Post subject: valarray subclass value assignment |
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Hi all
I have a subclass of valarray<T> thus
template <typename T>
class uo_val : public std::valarray<T>
{
public:
uo_val ( ) : std::valarray<T>() {}
uo_val (const int sz ) : std::valarray<T>( sz ) {}
uo_val (const int sz, const T fill ) : std::valarray<T>( fill, sz ) {}
//etc..
};
and I want to define an operator
uo_val& uo_val::operator=( const T & )
to assign all values to the supplied T using valarray's operator
valarray& valarray::operator=( const T & )
But neither (1) nor (2) below work and I'm not sure why.
uo_val& operator=( const T & val ) { // (1)
return std::valarray<T>::operator=( val );
}
Refuses to compile with:
error: invalid initialization of reference of type 'hr::uo_val<double>&'
from expression of type 'std::valarray<double>'
uo_val& operator=( const T & val ) { // (2)
*this = val;
return *this;
}
Compiles but gives runtime error signal 11 (SIGSEGV)
Could someone please enlighten me?
Many thanks
Michael
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Carl Barron
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| Posted: Sat Oct 29, 2005 8:17 pm Post subject: Re: valarray subclass value assignment |
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Michael Hopkins <michael.hopkins (AT) hopkins-research (DOT) com> wrote:
| Quote: | template <typename T
class uo_val : public std::valarray
{
public:
uo_val ( ) : std::valarray
uo_val (const int sz ) : std::valarray<T>( sz ) {}
uo_val (const int sz, const T fill ) : std::valarray<T>( fill, sz ) {}
//etc..
};
and I want to define an operator
uo_val& uo_val::operator=( const T & )
to assign all values to the supplied T using valarray's operator
valarray& valarray::operator=( const T & )
But neither (1) nor (2) below work and I'm not sure why.
uo_val& operator=( const T & val ) { // (1)
return std::valarray<T>::operator=( val );
}
Whats wrong with just using std::valarray<T>'s operator providing one |
explcitly for this class???
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Thomas Richter
Guest
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| Posted: Sun Oct 30, 2005 1:21 pm Post subject: Re: valarray subclass value assignment |
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Michael Hopkins wrote:
| Quote: | I have a subclass of valarray<T> thus
template <typename T
class uo_val : public std::valarray
{
public:
uo_val ( ) : std::valarray
uo_val (const int sz ) : std::valarray<T>( sz ) {}
uo_val (const int sz, const T fill ) : std::valarray<T>( fill, sz ) {}
//etc..
};
and I want to define an operator
uo_val& uo_val::operator=( const T & )
to assign all values to the supplied T using valarray's operator
valarray& valarray::operator=( const T & )
But neither (1) nor (2) below work and I'm not sure why.
uo_val& operator=( const T & val ) { // (1)
return std::valarray<T>::operator=( val );
}
Refuses to compile with:
error: invalid initialization of reference of type 'hr::uo_val<double>&'
from expression of type 'std::valarray<double>'
|
Because you return with the return value of operator= of the valarray
class, which is not of type uo_val.
| Quote: | uo_val& operator=( const T & val ) { // (2)
*this = val;
return *this;
}
Compiles but gives runtime error signal 11 (SIGSEGV)
|
Because this operator calls itself by its first line.
What about the following:
uo_val &operator=(const T &v) {
std::valarray<T>::operator=( v );
/*
** Now assign the members of v to the members of
** *this, whatever copying is required.
*/
// Finally, return the object itself back.
return *this;
}
So long,
Thomas
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Gabriel Dos Reis
Guest
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| Posted: Sun Oct 30, 2005 1:22 pm Post subject: Re: valarray subclass value assignment |
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Michael Hopkins <michael.hopkins (AT) hopkins-research (DOT) com> writes:
| Quote: | Hi all
I have a subclass of valarray<T> thus
template <typename T
class uo_val : public std::valarray
{
public:
uo_val ( ) : std::valarray
uo_val (const int sz ) : std::valarray<T>( sz ) {}
uo_val (const int sz, const T fill ) : std::valarray<T>( fill, sz ) {}
//etc..
};
and I want to define an operator
uo_val& uo_val::operator=( const T & )
to assign all values to the supplied T using valarray's operator
valarray& valarray::operator=( const T & )
But neither (1) nor (2) below work and I'm not sure why.
uo_val& operator=( const T & val ) { // (1)
return std::valarray<T>::operator=( val );
}
|
When you have
struct B { };
struct D : B { };
there is no implicit conversion from B& to D&, consequently (1) cannot
compile, because the return statement assumes there is such conversion.
| Quote: | Refuses to compile with:
error: invalid initialization of reference of type 'hr::uo_val<double>&'
from expression of type 'std::valarray<double>'
uo_val& operator=( const T & val ) { // (2)
*this = val;
return *this;
|
This is recursive definition, with no guard, therefore you get an
infinite loop.
None of the two problems has anything to do with valarray per se.
| Quote: | }
Compiles but gives runtime error signal 11 (SIGSEGV)
Could someone please enlighten me?
|
Is there a reason why you want to use inheritance instead of containment?
--
Gabriel Dos Reis
[email]gdr (AT) integrable-solutions (DOT) net[/email]
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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