Question

我有这样的头文件声明

#ifndef CONTAINER_H
#define CONTAINER_H

#include <map>
#include "object.h"

namespace memory {

template<class T>
class Collector {
};

template <class T>
class Collector<T*> {

private:
    std::map<std::string, T*> mem_storage;
public:
    std::string put_object(T* to_store);
    T* get_object(std::string key);
    void list_objects();
    void clean_up();
    void clean_object(std::string key); // force cleaning
    void mark_object_to_remove(std::string key); // mark unused
    void clean_removable(); // move to scheduled task

    ~Collector() {};
};

}

#endif

这样的实施

#include "../headers/container.h"

#define null nullptr

#include <iostream>
#include <string>

#include <boost/uuid/uuid.hpp>
#include <boost/uuid/uuid_generators.hpp>
#include <boost/uuid/uuid_io.hpp>
#include <boost/lexical_cast.hpp>

using namespace memory;

template<typename T>
void Collector<T*>::clean_object(std::string key) {
    int removed = mem_storage.erase(key);
    std::string removed_string = boost::lexical_cast<std::string>(removed);
}

template<typename T>
void Collector<T*>::clean_up() {
    mem_storage.clear();
}

template<typename T>
T* Collector<T*>::get_object(std::string key) {
    typename std::map<std::string, T*>::iterator it = mem_storage.find(key);
    if (it != mem_storage.end()) {
        return it->second;
    } else {
        return null;
    }
}

template<typename T>
void Collector<T*>::list_objects() {
    for (typename std::map<std::string, T*>::iterator it = mem_storage.begin(); it != mem_storage.end(); ++it) {
        std::cout << it->first << " => " << it->second->to_string() << std::endl;
    }
}

template<typename T>
std::string Collector<T*>::put_object(T* to_store) {
    boost::uuids::uuid uuid = boost::uuids::random_generator()();
    std::string key = boost::uuids::to_string(uuid);
    mem_storage[key] = to_store;
    return key;
}

template<typename T>
void Collector<T*>::mark_object_to_remove(std::string key) {
    mem_storage.find(key)->second->removable = true;
}

template<typename T>
void Collector<T*>::clean_removable() {
    typename std::map<std::string, T*>::iterator it = mem_storage.begin();
    while (it != mem_storage.end()) {
        std::string id = it->first;
        T instance = it->second;
        if (instance->removable) {
            mem_storage.erase(it++);
        } else {
            ++it;
        }
    }
}

我的主文件看起来像这样

#include <iostream>

#define byte unsigned char
#define null nullptr

#include "base/headers/object.h"
#include "base/headers/indexed_object.h"
#include "base/headers/container.h"
#include "base/headers/reflector.h"

void garbage_collection_prototype_example() {
    core::Object *io = runtime::RuntimeReflector::create_instance(
        "core::IndexedObject");
    core::Object *io_new = runtime::RuntimeReflector::create_instance("core::IndexedObject");
    std::cout << "Class 1 name: [" + io->get_class_name() + "]" << std::endl;
    std::cout << "Class 2 name: [" + io_new->get_class_name() + "]" << std::endl;

    bool is_same = io_new->is_same_instance(io);
    std::cout << "Is same: " << std::boolalpha << is_same << std::endl;

    memory::Collector<core::Object*> *garbage_collector = new memory::Collector<core::Object*>();
    std::string key = garbage_collector->put_object(io);
    std::string key_new = garbage_collector->put_object(io_new);
    garbage_collector->list_objects();

    garbage_collector->mark_object_to_remove(key);
    garbage_collector->clean_removable();

    garbage_collector->list_objects();

    garbage_collector->clean_up();
}

int main(int argc, char *argv[]) {
    garbage_collection_prototype_example();
    return 0;
}

但是当我尝试构建项目时，我有很多错误

D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:22: undefined reference to `memory::Collector<core::Object*>::put_object(core::Object*)'
D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:23: undefined reference to `memory::Collector<core::Object*>::put_object(core::Object*)'
D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:24: undefined reference to `memory::Collector<core::Object*>::list_objects()'
D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:26: undefined reference to `memory::Collector<core::Object*>::mark_object_to_remove(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:27: undefined reference to `memory::Collector<core::Object*>::clean_removable()'
D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:29: undefined reference to `memory::Collector<core::Object*>::list_objects()'
D:\c++\eclipse_workspace\SDLAttempts\Debug/../src/main.cpp:31: undefined reference to `memory::Collector<core::Object*>::clean_up()'

它无法看到Collector的任何方法。可能是由于我的基础非专业类Collector的空声明？但我尝试添加方法的实现，但没有帮助。

Answer 1

简短回答

您无法将功能模板的定义（实现）放入.cpp文件中。将它们放入声明它们的相同标题中。

<强>解释

这是因为函数模板在使用它们时会被实例化，因此编译器需要查看它们在任何使用位置的定义方式。有一些解决方法可以将定义与函数/类模板的声明分开，但是所有这些解决方案都意味着将模板的定义包含在使用它的转换单元中。

多个错误未定义对方法的引用

1 个答案: