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General / sfml game development book (2013) - chapter 2 enum issue

« on: February 08, 2023, 11:29:10 pm »

Hello SFML community x) , as I was following sfml game development book in chapter 2 where they implemented ResourceHolder class so I tried to use the class within the main but unfortunately I run into a linking error x( . I guess it has to do with the enum class TextureID . The error message says :

Severity        Code    Description     Project File    Line    Suppression State
Error   LNK2019 unresolved external symbol "public: __cdecl ResourceHolder<class sf::Texture,enum TexturesID>::~ResourceHolder<class sf::Texture,enum TexturesID>(void)" (??1?$ResourceHolder@VTexture@sf@@W4TexturesID@@@@QEAA@XZ) referenced in function main SFML    C:\Courses\CPP\Tutorial\Chapter 1\SFML\SFML\SFML.obj    1      
 

as for the source code for both ResourceHolder.h and ResourceHolder.cpp :

#ifndef RESOURCE_HOLDER_H
#define RESOURCE_HOLDER_H

#include <map>
#include <string>
#include <memory>
#include <stdexcept>
#include <cassert>
#include <SFML/Graphics.hpp>

template<typename Resource, typename Identifier>
class ResourceHolder
{
public:
        ResourceHolder();
        ~ResourceHolder();
public:
        void load(Identifier ID,const std::string& filename);

        template<typename Parameter>
        void load(Identifier ID, const std::string& filename, Parameter parameter);

        Resource& get(Identifier ID);
        const Resource& get(Identifier ID) const;

private:
        std::map <Identifier,
                std::unique_ptr<Resource> > mResourceMap;

};

#endif
 

#include "ResourceHolder.h"

template<typename Resource, typename Identifier>
void ResourceHolder<Resource, Identifier>::load(Identifier ID, const std::string& filename)
{
        std::unique_ptr<Resource> resourcePtr = std::make_unique<Resource>(new Resource());;

        if (!resourcePtr->loadFromFile(filename))
                throw std::runtime_error("ResourceHolder - Failed to load file : " + filename);

        auto inserted = mResourceMap.insert(std::make_pair(ID, std::move(resourcePtr)));
        assert(!inserted.second);

}

// this function is used when dealing with sahders, as loadFromFile function in shaders has two parameters
template<typename Resource, typename Identifier>
template<typename Parameter>
void ResourceHolder<Resource, Identifier>::load(Identifier ID, const std::string& filename, Parameter parameter)
{
        std::unique_ptr<Resource> resourcePtr = std::make_unique<Resource>(new Resource());

        if (!resourcePtr->loadFromFile(filename, parameter))
                throw std::runtime_error("ResourceHolder - Failed to load file : " + filename);

        auto inserted =  mResourceMap.insert(std::make_pair(ID,std::move(resourcePtr))) ;
        assert(!inserted.second && "ResourceHolder<Resource, Identifier>::load : function that takes 3 parameters");
}


template<typename Resource, typename Identifier>
Resource& ResourceHolder<Resource, Identifier>::get(Identifier ID)
{
        auto found = mResourceMap.find(ID);
        assert(found != mResourceMap.end() && "the given ID already exist in mResourceMap");

        return found->second;

}

template<typename Resource, typename Identifier>
const Resource& ResourceHolder<Resource, Identifier>::get(Identifier ID) const
{
        auto found = mResourceMap.find(ID);
        assert(found != mResourceMap.end() && "the given ID already exist in mResourceMap");

        return *found->second;
}

 

as for the error, it occurs when i declare a variable with ResourceHolder class .

ResourceHolder<sf::Texture,TextureID>

as for the enum it's declared in main.cpp as follow :

enum class TextureID{
Eagle,
};