单例class的成员变量的生命周期是多少?
What is the life time of a singleton class's member variables?
class Member {
public:
Member(int idx) {
this->idx_ = idx;
}
int get_idx() {
return idx_;
}
void set_idx(int idx) {
this->idx_ = idx;
}
void foo();
private:
int idx_;
};
class SingletonClass {
public:
static SingletonClass& GetInstance() {
static SingletonClass inst;
return inst;
}
vector<Member*> get_members() {
return this->members_;
}
Member* get_member(int idx) {
return this->members_[idx];
}
void add_member(Member* mem) {
this->members_.push_back(mem);
}
private:
SingletonClass() {}
vector<Member*> members_;
};
void Member::foo() {
SingletonClass inst = SingletonClass::GetInstance();
cout << inst.get_members().size();
}
int main() {
SingletonClass inst = SingletonClass::GetInstance();
inst.add_member(new Member(0));
inst.add_member(new Member(1));
cout << inst.get_members().size() << endl;
Member* mem = inst.get_member(1);
mem->foo();
return 0;
}
输出为
2
0
好像在Member::foo()
里面拿到SingletonClass的实例的时候,SingletonClass
的成员变量vectormembers_
就被清空了...谁能给我解释一下为什么以及如何这会发生吗?我怎样才能修复它以获得预期的结果?非常感谢!
It seems that when I get the instance of SingletonClass
inside Member::foo()
, the member variable vector members_
of SingletonClass
is cleared... Can anyone explain to me why and how this happen? And how can I fix it to get expected result?
您正在复制以下行中的对象:
SingletonClass inst = SingletonClass::GetInstance();
然后你正在修改副本的内容。原始对象保持不变。
使用:
SingletonClass& inst = SingletonClass::GetInstance();
为防止这种情况在代码的其他地方发生,请显式删除复制构造函数和复制赋值运算符。
private:
SingletonClass() {}
SingletonClass(SingletonClass const&) = delete;
SingletonClass& operator=(SingletonClass const&) = delete;
vector<Member*> members_;
class Member {
public:
Member(int idx) {
this->idx_ = idx;
}
int get_idx() {
return idx_;
}
void set_idx(int idx) {
this->idx_ = idx;
}
void foo();
private:
int idx_;
};
class SingletonClass {
public:
static SingletonClass& GetInstance() {
static SingletonClass inst;
return inst;
}
vector<Member*> get_members() {
return this->members_;
}
Member* get_member(int idx) {
return this->members_[idx];
}
void add_member(Member* mem) {
this->members_.push_back(mem);
}
private:
SingletonClass() {}
vector<Member*> members_;
};
void Member::foo() {
SingletonClass inst = SingletonClass::GetInstance();
cout << inst.get_members().size();
}
int main() {
SingletonClass inst = SingletonClass::GetInstance();
inst.add_member(new Member(0));
inst.add_member(new Member(1));
cout << inst.get_members().size() << endl;
Member* mem = inst.get_member(1);
mem->foo();
return 0;
}
输出为
2
0
好像在Member::foo()
里面拿到SingletonClass的实例的时候,SingletonClass
的成员变量vectormembers_
就被清空了...谁能给我解释一下为什么以及如何这会发生吗?我怎样才能修复它以获得预期的结果?非常感谢!
It seems that when I get the instance of
SingletonClass
insideMember::foo()
, the member variable vectormembers_
ofSingletonClass
is cleared... Can anyone explain to me why and how this happen? And how can I fix it to get expected result?
您正在复制以下行中的对象:
SingletonClass inst = SingletonClass::GetInstance();
然后你正在修改副本的内容。原始对象保持不变。
使用:
SingletonClass& inst = SingletonClass::GetInstance();
为防止这种情况在代码的其他地方发生,请显式删除复制构造函数和复制赋值运算符。
private:
SingletonClass() {}
SingletonClass(SingletonClass const&) = delete;
SingletonClass& operator=(SingletonClass const&) = delete;
vector<Member*> members_;