Error compiling template based class

[maverick]

Hello

I am getting an error when i am trying to instantiate an object of the
template based class

#include "foo.h"
int main()
{



CFoo<int> myFoo ;
return 1 ;
}





now I have 2 files
foo.h
---------------------------------------------------

template < class CFooTemp> class CFoo
{
CFoo();
~CFoo() ;


};




foo.cpp
--------------------------------------------
#include "foo.h"



template < class CFooTemp>
CFoo<CFooTemp>::CFoo()
{

}




template < class CFooTemp>
CFoo<CFooTemp>::CFoo()
{

}




------------------------------------------------------------

I get the following errors

main.cpp:12: undefined reference to `CFoot<int>::CFoo()'

main.cpp:14: undefined reference to `CFoo<int>::~CFoo()'




However this error is not seen when i include "foo.cpp" instead of foo.h

 

[Victor Bazarov]

Hello

I am getting an error when i am trying to instantiate an object of the
template based class

RTFFAQ

V

 

[mlimber]

Hello

I am getting an error when i am trying to instantiate an object of the
template based class

#include "foo.h"
int main()
{



CFoo<int> myFoo ;
return 1 ;
}





now I have 2 files
foo.h
---------------------------------------------------

template < class CFooTemp> class CFoo
{
CFoo();
~CFoo() ;


};




foo.cpp
--------------------------------------------
#include "foo.h"



template < class CFooTemp>
CFoo<CFooTemp>::CFoo()
{

}




template < class CFooTemp>
CFoo<CFooTemp>::CFoo()
{

}




------------------------------------------------------------

I get the following errors

main.cpp:12: undefined reference to `CFoot<int>::CFoo()'

main.cpp:14: undefined reference to `CFoo<int>::~CFoo()'




However this error is not seen when i include "foo.cpp" instead of foo.h

Please consult this group's FAQs:

http://www.parashift.com/c++-faq-lite/templates.html#faq-35.12

Cheers! --M

 

[Martin Steen]

main.cpp:12: undefined reference to `CFoot<int>::CFoo()'

main.cpp:14: undefined reference to `CFoo<int>::~CFoo()'

This is a linker error. The linker doesn't know where
the code for CFoo is.

Add the file foo.cpp to your projekt/makefile. You have
to tell the compiler what files to compile and to link.

However this error is not seen when i include "foo.cpp" instead of foo.h

Of course you can include all .cpp-files into the mainfile (main.cpp).
But this would result in long compile times and a code that is
very hard to maintain.

-Martin

 

[red floyd]

This is a linker error. The linker doesn't know where
the code for CFoo is.

No, Martin, it's a template instantiation issue.
http://www.parashift.com/c++-faq-lite/templates.html#faq-35.12

 

[Martin Steen]

No, Martin, it's a template instantiation issue.
http://www.parashift.com/c++-faq-lite/templates.html#faq-35.12

Ups, of course you're right. That's why it's good to have templates
in a .hpp include file.

-Martin

 

[Greg Comeau]

I am getting an error when i am trying to instantiate an object of the
template based class

#include "foo.h"
int main()
{
CFoo<int> myFoo ;
return 1 ;
}

now I have 2 files
foo.h
---------------------------------------------------

template < class CFooTemp> class CFoo
{
CFoo();
~CFoo() ;
};

foo.cpp
--------------------------------------------
#include "foo.h"

template < class CFooTemp>
CFoo<CFooTemp>::CFoo()
{
}

template < class CFooTemp>
CFoo<CFooTemp>::CFoo()
{
}

------------------------------------------------------------

I get the following errors

main.cpp:12: undefined reference to `CFoot<int>::CFoo()'
main.cpp:14: undefined reference to `CFoo<int>::~CFoo()'

However this error is not seen when i include "foo.cpp" instead of foo.h

Check out http://www.comeaucomputing.com/techtalk/templates/#whylinkerror

 

[red floyd]

Ups, of course you're right. That's why it's good to have templates
in a .hpp include file.

No biggie, we've all made oopses here.

I'm sure you'll correct one of my posts next time

 

[Greg Comeau]

This is a linker error. The linker doesn't know where
the code for CFoo is.

Add the file foo.cpp to your projekt/makefile. You have
to tell the compiler what files to compile and to link.

That's insufficient because instantiation throws in some
curves over the traditional linker. See
http://www.comeaucomputing.com/techtalk/templates/#whylinkerror