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To instantiate a template function explicitly, follow the template keyword by a declaration (not definition) for the function, with the function identifier followed by the template arguments. template float twice<float>(float original); Template arguments may be omitted when the compiler can infer them.
template <typename T> ... This means exactly the same thing as the previous instance. The typename and class keywords can be used interchangeably to state that a template parameter is a type variable (as opposed to a non-type template parameter).
Defining a Function TemplateA function template starts with the keyword template followed by template parameter(s) inside <> which is followed by the function definition. In the above code, T is a template argument that accepts different data types ( int , float , etc.), and typename is a keyword.
I have a class named "SimObject":
namespace simBase
{
class __declspec(dllexport) SimObject: public SimSomething
{
public:
template <class T>
void updateParamValue( const std::string& name, T val );
}
}
I have another class named "ITerrainDrawable":
namespace simTerrain
{
class __declspec(dllexport) ITerrainDrawable : public simBase::SimObject
{
}
}
These classes are in different libraries. SimObject is in simBase, ITerrainDrawable is in simTerrain libraries. Even if ITerrainDrawable is derived from SimObject and I included library of simBase, I get a link error:
unresolved external symbol
1>ITerrainDrawable.obj : error LNK2019: unresolved external symbol "public: void __thiscall simBase::SimObject::updateParamValue<float>(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,float)" (??$updateParamValue@M@SimObject@simBase@@QAEXABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@M@Z) referenced in function "public: void __thiscall simTerrain::ITerrainDrawable::setTerrainSize(float)" (?setTerrainSize@ITerrainDrawable@simTerrain@@QAEXM@Z)
1>ITerrainDrawable.obj : error LNK2019: unresolved external symbol "public: void __thiscall simBase::SimObject::updateParamValue<class osg::Vec4f>(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class osg::Vec4f)" (??$updateParamValue@VVec4f@osg@@@SimObject@simBase@@QAEXABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@VVec4f@osg@@@Z) referenced in function "public: void __thiscall simTerrain::ITerrainDrawable::setSatelliteTextureBorders(class osg::Vec2f,class osg::Vec2f)" (?setSatelliteTextureBorders@ITerrainDrawable@simTerrain@@QAEXVVec2f@osg@@0@Z)
Why do I get this error?
Everything works fine if I don't use template function but I need it.
If I move this function to simTerrain library it works fine but I don't want to use duplicate function because there are many libraries like simTerrain.
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