我正在尝试创建线程安全的单例类,这是我的代码:
#include<iostream>
#include<mutex>
using namespace std;
std::mutex mtx;
class MySingleton{
private:
static MySingleton * singletonInstance;
MySingleton();
MySingleton(const MySingleton&);
const MySingleton& operator=(const MySingleton&);
~MySingleton();
public:
static MySingleton* GetInstance();
void foo();
};
MySingleton::MySingleton(){
std::cout << "Ctor\n";
};
MySingleton::~MySingleton(){
std::cout << "Dtor\n";
};
void MySingleton::foo()
{
cout << "Inside Foo" << endl;
}
MySingleton* MySingleton::GetInstance(){
//double check
if (singletonInstance == NULL){
std::lock_guard<std::mutex> lock(mtx);
if (singletonInstance == NULL)
singletonInstance = new MySingleton();
}
return singletonInstance;
}
int main(void){
MySingleton::GetInstance()->foo();
}
我在VS2015中执行了此代码,发现了以下错误:
1>Source.obj : error LNK2001: unresolved external symbol "private: static class MySingleton * MySingleton::singletonInstance" (?singletonInstance@MySingleton@@0PAV1@A)
1>E:\CPP\Test\Debug\Singleton.exe : fatal error LNK1120: 1 unresolved externals
我不确定代码中缺少什么,只想用单例实例调用foo()。谁能帮忙找出错误原因?
答案 0 :(得分:2)
在C ++中,您需要在类之外的{em>源(.cpp)文件中初始化static
成员 ,如下所示:
/** your singleton class definition **/
MySingleton* MySingleton::singletonInstance = nullptr;
/** rest of your code **/