Template Member function undfined

[Xillez]

I have a problem with undefined templated member function used in main.

Error:
"CMakeFiles/Framework.dir/source/src/main.cpp.o: In function `main':
main.cpp:(.text+0x33): undefined reference to `unsigned int EntityMgr::createEntity<Entity>()'"

Can someone please help me understand why the EntityMgr::createEntity function is undefined from main?

Current setup (simplified):

//EntityMgr.hpp
#include "Entity.hpp"
class EntityMgr
{
    template<typename>
    unsigned int createEntity();
}
 
// Entity.hpp:
class Entity
{
    //
};
 

EntityMgr.cpp:

template<typedef Class>
unsigned int EntityMgr::createEntity()
{
    ...
}
 

main.cpp:

#include "EntityMgr.hpp"
 
int main()
{
    EntityMgr entityMgr;
    entityMgr.createEntity<Entity>();  <--- Problem line.
    return 0;
}
 

[weaknessforcats]

I fixed your code. Look how I parameterize template<> and compare to the original code. Using "typedef" or "typename" is bogus because those are not types. Using "class T" defines T as a type. That is the T used by the precompiler to generate your specialized template function.

Also be clear on these terms: A template function is the function generated by the precompiler from a function template.

These two terms are often mixed up and this can lead to confusion when trying to understand how things work.

//EntityMgr.hpp
//#include "Entity.hpp"
class EntityMgr
{
public:
 
    template<class T>
    unsigned int createEntity();
};
 
// Entity.hpp:
class Entity
{
    //
};
 
template<class T >
unsigned int EntityMgr::createEntity()
{
    return 0;  //for compile only
}
 
//#include "EntityMgr.hpp"
 
int main()
{
    EntityMgr entityMgr;
    entityMgr.createEntity<Entity>();  //<-- - Problem line.
        return 0;
}