Problem with static variable in template class

[StephQ]

In utility.hpp I have:

namespace utility
{

template <class T, double (T::*F)(double) const>
class Display
{
private:
static double resolution;
static double margin;

public:
static void computePlot(stringstream& ss, const T& t, const
ClosedInterval& interval);
};

}

In utility.cpp:

#include <utility.hpp>
namespace utility
{

template <class T, double (T::*F)(double) const>
double Display<T,F>::resolution = 0.025;

template <class T, double (T::*F)(double) const>
double Display<T,F>::margin = 5;

}

Then I have another cpp file in which I'm including utility.hpp and
calling the computePlot function using:

utility::Display<EnvelopePiece, &EnvelopePiece::f>::computePlot( ss,
*this, interval );

(the *this because I'm inside a member function of the EnvelopePiece
class when I'm calling computePlot)

However when compiling I get:
1>envelope.obj : error LNK2001: unresolved external symbol "private:
static double utility::Display<class EnvelopePiece,&public: double
__thiscall EnvelopePiece::f(double)const >::resolution" (?resolution@?
$Display@VEnvelopePiece@@$1?f@1@QBENN@Z@utility@@0 NA)

Like if the static variables were not declared.
But isn't double Display<T,F>::resolution the proper way to declare
the "generic" template static variable, that I can then specialize if
I want to?

Thanks

StephQ

[StephQ]

On May 3, 9:00 pm, StephQ <[e-mail]:

In utility.hpp I have:

namespace utility
{

template <class T, double (T::*F)(double) const>
class Display
{
private:
static double resolution;
static double margin;

public:
static void computePlot(stringstream& ss, const T& t, const
ClosedInterval& interval);

};
}

In utility.cpp:

#include <utility.hpp>
namespace utility
{

template <class T, double (T::*F)(double) const>
double Display<T,F>::resolution = 0.025;

template <class T, double (T::*F)(double) const>
double Display<T,F>::margin = 5;

}

Then I have another cpp file in which I'm including utility.hpp and
calling the computePlot function using:

utility::Display<EnvelopePiece, &EnvelopePiece::f>::computePlot( ss,
*this, interval );

(the *this because I'm inside a member function of the EnvelopePiece
class when I'm calling computePlot)

However when compiling I get:
1>envelope.obj : error LNK2001: unresolved external symbol "private:
static double utility::Display<class EnvelopePiece,&public: double
__thiscall EnvelopePiece::f(double)const >::resolution" (?resolution@?
$Display@VEnvelopePiece@@$1?f@1@QBENN@Z@utility@@0 NA)

Like if the static variables were not declared.
But isn't double Display<T,F>::resolution the proper way to declare
the "generic" template static variable, that I can then specialize if
I want to?

Thanks

StephQ

I forgot....
Should I put the declarations inside utility.hpp instead?

Cheers
StephQ

[Fei Liu]

StephQ wrote:

On May 3, 9:00 pm, StephQ <[e-mail]:

>In utility.hpp I have:

namespace utility
{

template <class T, double (T::*F)(double) const>
class Display
{
private:
static double resolution;
static double margin;

public:
static void computePlot(stringstream& ss, const T& t, const
ClosedInterval& interval);

};
}

In utility.cpp:

#include <utility.hpp>
namespace utility
{

template <class T, double (T::*F)(double) const>
double Display<T,F>::resolution = 0.025;

template <class T, double (T::*F)(double) const>
double Display<T,F>::margin = 5;

}

Then I have another cpp file in which I'm including utility.hpp and
calling the computePlot function using:

utility::Display<EnvelopePiece, &EnvelopePiece::f>::computePlot( ss,
*this, interval );

(the *this because I'm inside a member function of the EnvelopePiece
class when I'm calling computePlot)

However when compiling I get:
1>envelope.obj : error LNK2001: unresolved external symbol "private:
static double utility::Display<class EnvelopePiece,&public: double
__thiscall EnvelopePiece::f(double)const >::resolution" (?resolution@?
$Display@VEnvelopePiece@@$1?f@1@QBENN@Z@utility@@ 0NA)

Like if the static variables were not declared.
But isn't double Display<T,F>::resolution the proper way to declare
the "generic" template static variable, that I can then specialize if
I want to?

Thanks

StephQ

I forgot....
Should I put the declarations inside utility.hpp instead?

Cheers
StephQ

You shouldn't need utility.cpp. Put everything in utility.hpp. In your
case, the compiler couldn't see utility.cpp and couldn't properly
compile those static members (class variables).

[StephQ]

You shouldn't need utility.cpp. Put everything in utility.hpp. In your
case, the compiler couldn't see utility.cpp and couldn't properly
compile those static members (class variables).

Thank you, now it works.
I was confused about the syntax, but it completely makes sense.

StephQ