C++ 向量问题 - 'LNK2001：未解析的外部符号私有：静态...'
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C++ vector issue - 'LNK2001: unresolved external symbol private: static...'
提问by oliverw92
Before anyone calls me out for not looking at pre-existing questions, I have looked and realise that it is to do with declaration, but I still can't get it to work (might be something to do with me using vectors).
在有人因为没有查看预先存在的问题而叫我出去之前，我已经查看并意识到它与声明有关，但我仍然无法让它工作（可能与我使用向量有关）。
Manager.h:
经理.h：
#include "Flight.h"
#ifndef manager_h
#define manager_h
class Manager {
static vector<Airport> airports;
static vector<Flight> flights;
public:
static void loadAirports();
static void loadFlights();
static Airport getAirport(string code);
static vector<string> split(const string &s, vector<string> &elems);
};
#endif
Manager.cpp:
管理器.cpp：
#include "Manager.h"
void Manager::loadAirports ()
{
ifstream airportfile("airports.txt");
string line;
while (getline(airportfile, line))
{
vector<string> values;
split(line, values);
Airport airport (values[0], values[1], atoi(values[2].c_str()));
airports.push_back(airport);
}
}
void Manager::loadFlights ()
{
ifstream flightfile("flights.txt");
string line;
while (getline(flightfile, line))
{
vector<string> values;
split(line, values);
Flight flight (getAirport(values[0]), getAirport(values[1]), atoi(values[2].c_str()), atoi(values[3].c_str()));
flights.push_back(flight);
}
cout << flights.size() << endl;
}
Airport Manager::getAirport (string code)
{
for (int i = 1; i < (int)airports.size(); i++)
{
if (airports[i].code == code)
return airports[i];
}
throw exception();
}
vector<string> Manager::split(const string &s, vector<string> &elems) {
stringstream ss(s);
string item;
while(getline(ss, item, ',')) {
elems.push_back(item);
}
return elems;
}
It is throwing this error:
它抛出这个错误：
Manager.obj : error LNK2001: unresolved external symbol "private: static struct Vector Manager::airports" (?airports@Manager@@0U?$Vector@UAirport@@@@A)
Manager.obj : error LNK2001: unresolved external symbol "private: static struct Vector Manager::flights" (?flights@Manager@@0U?$Vector@UFlight@@@@A)
Manager.obj：错误 LNK2001：未解析的外部符号“私有：静态结构向量管理器::机场”（?airports@Manager@@0U?$Vector@UAirport@@@@A）
Manager.obj：错误 LNK2001：未解析的外部符号“私有：静态结构向量管理器::航班”（?flights@Manager@@0U?$Vector@UFlight@@@@A）
I realise i need to define the vectors, but how and where? I tried creating an empty constructor and then doing
我意识到我需要定义向量，但是如何以及在哪里定义？我尝试创建一个空的构造函数然后做
Manager::Manager ()
{
vector<string> flights;
vector<string> airports;
}
But it just gave me a re-definition error.
但它只是给了我一个重新定义错误。
回答by Constantinius
You have to define them in the .cppfile:
您必须在.cpp文件中定义它们：
vector<string> Manager::flights;
vector<string> Manager::airports;
回答by Oliver Charlesworth
In your .cpp file, you need to add the definitionsof the static variables:
在您的 .cpp 文件中，您需要添加静态变量的定义：
vector<Airport> Manager::airports;
vector<Flight> Manager::flights;
See Why are classes with static data members getting linker errors?from the C++ FAQ.
请参阅为什么具有静态数据成员的类会收到链接器错误？来自 C++ 常见问题解答。
回答by Gavin Lock
Oli and Constantinius have answered your actual question, but I would recommend changing the class. As it stands it has only static members, so you can never create an object of this class. While this is legal C++, it is not in the spirit of C++ (Although there are other languages that do embrace this usage, such as C#)
Oli 和 Constantinius 已经回答了您的实际问题，但我建议更改课程。就目前而言，它只有静态成员，因此您永远无法创建此类的对象。虽然这是合法的 C++，但它不符合 C++ 的精神（尽管还有其他语言确实接受了这种用法，例如 C#）
All static members imply that you are trying for some kind of singleton, but there are more standard ways of enforcing the singleton-ness of a class.
所有静态成员都暗示您正在尝试某种单例，但有更多标准方法可以强制执行类的单例性。
Having said that - I advocate neverbuilding singleton-ness intoa class. Rather write the class as a normal class, and provide a singleton wrapper. This also has the neat side effect of preventing the notorious static initialization order fiascothat your current code is liable to bump into.
话虽如此 - 我主张永远不要将单例性构建到一个类中。而是将类编写为普通类，并提供单例包装器。这也有一个巧妙的副作用，可以防止您当前的代码可能遇到的臭名昭著的静态初始化顺序失败。
So, something like (excluding the includes for brevity):
因此，类似于（为简洁起见，不包括包含在内）：
Manager.h
经理.h
class Manager {
vector<Airport> airports;
vector<Flight> flights;
public:
Manager();
void loadAirports();
void loadFlights();
Airport getAirport(string code);
vector<string> split(const string &s, vector<string> &elems);
};
Manager& GetManager();
Manager.cpp
管理器.cpp
Manager::Manager()
{
loadAirports();
loadFlights();
}
Manager& GetManager()
{
static Manager manager;
return manager;
}
