calling a function template from a second class

Question

I’m trying to call a function template defined inside a class from within another class, but I’m stuck.
I get error:

1>class1.obj : error LNK2019: riferimento al simbolo esterno "public: void __thiscall class2::output<double,long>(double,long,float)" (??$output@NJ@class2@@QAEXNJM@Z) non risolto nella funzione "public: void __thiscall class1::x(class class2 &)" (?x@class1@@QAEXAAVclass2@@@Z)

1>class1.obj : error LNK2019: riferimento al simbolo esterno "public: void __thiscall class2::output<float,int>(float,int,float)" (??$output@MH@class2@@QAEXMHM@Z) non risolto nella funzione "public: void __thiscall class1::y(class class2 &)" (?y@class1@@QAEXAAVclass2@@@Z)

1>C:\xxx.exe : fatal error LNK1120: 2 esterni non risolti

If I uncomment lines with duplicate functions (the ones without templates) it is ok. Can you help fix it?

File: “class1.h”

#ifndef CLASS1
#define CLASS1
#include "class2.h"
class class1{
public:
void x(class2& c );
void y(class2& c );
};
#endif

File: “class1.cpp”

#include "class1.h"
void class1::x( class2& c )
{
double img;
long integ;
float y;
c.output(img, integ, y);
}
void class1::y(class2& c )
{
float img;
int integ;
float y;
c.output(img, integ, y);
}

File: “class2.h”

#ifndef CLASS2
#define CLASS2
class class2{
void output2(double img, long integ, float y);
void output2(float img, int integ, float y);
public:
template <typename T1, typename T2>
void output(T1 img, T2 integ, float y);
//void output(double img, long integ, float y);
//void output(float img, int integ, float y);
};
#endif

File: “class2.cpp”

#include "class2.h"
template <typename T1, typename T2>
void class2::output(T1 img, T2 integ, float y)
{output2(img, integ, y);}
//void class2::output(double img, long integ, float y)
//{output2(img, integ, y);}
//void class2::output(float img, int integ, float y)
//{ output2(img, integ, y);}
void class2::output2(double img, long integ, float y){/*...*/}
void class2::output2(float img, int integ, float y){/*...*/}

EDIT

I’m talking about function templates and not class templates. I’ve seen the question I would be duplicating before, but it is not what I’m looking for. I have two functions inside a class that are identical except for their parameters type.

I only wanted a simple trick to avoid writing and maintaining identical code for two functions inside the same class. Anyway I’ve found a solution, adding these two lines at the bottom of class2.cpp:

template void class2::output<double, long>(double img, long integ, float y);
template void class2::output<float, int>(float img, int integ, float y);

My question has been downvoted and marked as duplicate, but it seems to me that the original question is about template classes (or structs) and not template member functions. Anyway I've tryed to put the code of void output(T1 img, T2 integ, float y) inside the header file and the error doesn't disappear. — Giuseppe Dini, Jul 07 '15 at 16:57

score 0 · Answer 1 · answered Jul 08 '15 at 06:39

If you want a specialization you need to implement the "default" template function in the .h file and define which specializations you are implementing. In the .cpp file you simply implement the specializations.

File: "class2.h"

#ifndef CLASS2
#define CLASS2
class class2{
    public:
        template <typename T1, typename T2>
        void class2::output(T1 img, T2 integ, float y)
        { /* .. do stuff.. */}
};
template <>
void class2::output(double img, long integ, float y);
#endif

File: “class2.cpp”

#include "class2.h"
template <>
void class2::output(double img, long integ, float y)
{ /* .. do specialized stuff.. */}

calling a function template from a second class

1 Answers1