[英]Invalid use of non-static member function c++
I am following this example . 我正在关注这个例子 。 But when I compile, it returns an error: 但是当我编译时,它会返回一个错误:
Invalid use of non-static member function 无效使用非静态成员函数
at the line 在线
void(Machine:: *ptrs[])() =
{
Machine::off, Machine::on
};
I tried to add static
to void on();
我试图void on();
添加static
到void on();
at class 在课堂上
class Machine
{
class State *current;
public:
Machine();
void setCurrent(State *s)
{
current = s;
}
static void on(); // I add static here ...
static void off(); // and here
};
But it complains that 但它抱怨说
Invalid use of member Machine::current in static member function 在静态成员函数中使用成员Machine :: current无效
Can you help me fix this? 你能帮我解决这个问题吗?
Unlike static member functions or free functions, non-static member functions won't implicitly convert to member function pointers. 与静态成员函数或自由函数不同,非静态成员函数不会隐式转换为成员函数指针。
(emphasis mine) (强调我的)
An lvalue of function type
T
can be implicitly converted to a prvalue pointer to that function. 函数类型T
的左值可以隐式转换为该函数的prvalue指针。 This does not apply to non-static member functions because lvalues that refer to non-static member functions do not exist. 这不适用于非静态成员函数,因为不存在引用非静态成员函数的左值。
So you need to use &
explicitly to take the address of the non-static member functions (ie to get non-static member function pointers). 因此,您需要使用&
explicit来获取非静态成员函数的地址(即获取非静态成员函数指针)。 eg 例如
void(Machine:: *ptrs[])() =
{
&Machine::off, &Machine::on
};
If you declare them as static member function, you should change the type of ptrs
(to array of non-member function pointers). 如果将它们声明为静态成员函数,则应更改ptrs
的类型(到非成员函数指针的数组)。 Note that for static member function it's fine to not use &
explicitly. 请注意,对于静态成员函数,可以不使用&
explicit。 eg 例如
void(*ptrs[])() =
{
Machine::off, Machine::on
};
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.