如何解决“错误LNK2019：无法解析的外部符号”？

如何解决如何解决“错误LNK2019：无法解析的外部符号”？

因此，我最近开始学习C ++，几天前，我开始关注有关实体组件系统的教程，但由于遇到以下错误而陷入困境：

错误LNK2019：未解决的外部符号“ public：void __thiscall ComponentArray > :: insertEntity（unsigned int，class std :: bitset ）” ...中引用函数_SDL_main

过去几天，我一直在寻找答案，但是我找不到解决方法。我正在使用Visual Studio，并且所有文件都添加到了项目的解决方案资源管理器中，我还发现，如果只在头文件中键入所有内容，而忽略cpp文件，则它的工作效率为零。另一件事是，当我尝试在main.cpp文件中对其进行测试之前，它给我带来了问题，然后一切都编译了。

ComponentArray.cpp

#include "ComponentArray.h"

template <typename T>
void ComponentArray<T>::insertEntity(Entity entity,T component)
{
    //Getting a new index and incrementing the count.
    size_t new_index = entities_created++;

    //Updating the maps to the newly added entity.
    entity_to_index[entity] = new_index;
    index_to_entity[new_index] = entity;

    //Inserting new entity.
    component_array[new_index] = component;

}

template <typename T>
void ComponentArray<T>::removeEntity(Entity entity)
{
    //Entities will be destroyed by swapping places with the last entity in array.
    //and then removing it,this way the array will always be packed.
    size_t removed_index = entity_to_index[entity];
    size_t last_index = entities_created - 1;
    Entity last_entity = index_to_entity[last_index];

    //Updating maps.
    entity_to_index[last_entity] = removed_index;
    index_to_entity[removed_index] = last_entity;

    //Cleaning maps.
    entity_to_index.erase(entity);
    index_to_entity.erase(last_index);

    //Updating array.
    component_array[removed_index] = component_array[last_index];

}

template <typename T>
void ComponentArray<T>::entityDestroyed(Entity entity)
{
    if (entity_to_index.find(entity) != entity_to_index.end())
    {
        removeEntity(entity);
    }
    else printf("The entity does not exist in the mapping.");
}

template <typename T>
T& ComponentArray<T>::getData(Entity entity)
{
    assert(entity_to_index.find(entity) != entity_to_index.end() && "The entity does not exist inside the mappings.");

    return component_array[entity_to_index[entity]];
}

ComponentArray.h

#pragma once

#include <unordered_map>
#include <assert.h>
#include <iostream>
#include <stdio.h>

#include "Types.h"

class IComponentArray
{
public:
    virtual ~IComponentArray() = default;
    virtual void entityDestroyed(Entity entity) = 0;
};

template <typename T>
class ComponentArray : public IComponentArray
{
public:
    void insertEntity(Entity entity,T component);
    void removeEntity(Entity entity);
    void entityDestroyed(Entity entity);
    T& getData(Entity entity);

private:
    //This array will keep track of the components assigned to an entity.
    std::array<T,MAX_ENTITIES> component_array;

    std::unordered_map<Entity,size_t> entity_to_index;
    std::unordered_map<size_t,Entity> index_to_entity;
 
    //total entities count = entities_created - 1 (friendly reminder)
    size_t entities_created = 0;
};

main.cpp

#include <SDL.h>
#include <SDL_image.h>
#include <stdio.h>
#include <iostream>

#include "Game.h"
#include "EntityManager.h"
#include "ComponentArray.h"


int main(int argc,char* argv[])
{
    Game* main_game = new Game("MUGEN",SDL_WINDOWPOS_CENTERED,800,600);
    
    //After adding this I started having problems.
    ComponentArray<Signature> components = ComponentArray<Signature>();

    Signature generic(1); //bitset
    components.insertEntity(0,generic);

    Signature test = components.getData(0);

    std::cout << test << std::endl;

    while (main_game->isRunning())
    {
        main_game->handleEvents();
        main_game->update();
        main_game->render();
    }

    delete main_game;

    return 0;
}