问题
My question is actually regarding already asked question. I have tried the answer given by @r3mus n0x also have seen some SO questions which did not help me to get a clear idea about the above situation.
In the given post lacks MCVE, therefore I have tried a bit and came up with the following code and with the same error what @user10213044 mentioned in his/her post.
Error msg
error C2065: 'm_func': undeclared identifier
My qestion:
Q1: Can we really store the pointer to some of the member functions of a class(like in the following example) into it's on private member(ex. vector array)? If so what is the reason for the above error msg?
Q2: I have also tried to write inside the for loop:
classFuncPtr fun = bindClassPtr->m_func; // compiles
fun(str); // error
gave me: Error msg
error: must use '.*' or '->*' to call pointer-to-member function in 'fun (...)', e.g. '(... ->* fun) (...)'
fun(str); // error
which I could not understand. Can anybody tell me what went wrong in this case?
The second attempt was similar to the following case which we use for normal functions pointer case.
typedef void(*FuncPtr)(const std::string&);
FuncPtr Lambda = [](const std::string& str) { std::cout << str << std::endl; };
Lambda(std::string("Hellow World"));
Here is the code I tried:
#include <iostream>
#include <vector>
#include <string>
#include <memory>
class MyClass;
typedef void (MyClass::*classFuncPtr)(const std::string&); // function ptr to MyClass::member functions
struct MyBind // bind struct
{
classFuncPtr m_func;
explicit MyBind(const classFuncPtr& func): m_func(std::move(func)) {}
};
class MyClass
{
std::string m_var;
std::vector<std::unique_ptr<MyBind>> my_binds_;
public:
MyClass() // constructor
{
my_binds_.emplace_back( std::make_unique<MyBind>( std::move(&MyClass::do_this) ));
my_binds_.emplace_back( std::make_unique<MyBind>( std::move(&MyClass::do_that) ));
}
// two functions to bind
void do_this (const std::string& str) { std::cout << "From do this: " << str << std::endl; }
void do_that (const std::string& str) { std::cout << "From do that: " << str << std::endl; };
void handle_input(const std::string& str)
{
for (const std::unique_ptr<MyBind>& bindClassPtr: my_binds_)
{
// how to print passed string str here?? (Q1)
(bindClassPtr->*m_func)(str);
/*
classFuncPtr fun = bindClassPtr->m_func; // compiles (Q2)
fun(str); // error
*/
}
}
};
回答1:
Your first attempt fails because there's no variable in scope named m_func.
Your second attempt fails because a pointer-to-member requires an object to be called on.
The correct syntax is:
classFuncPtr fun = bindClassPtr->m_func;
(this->*fun)(str);
Live Demo
The pointer contained in your MyBind objects isn't actually bound to anything. It's a pointer to a member of MyClass, so you have to provide it an instance of MyClass to work on.
来源：https://stackoverflow.com/questions/51904472/how-to-call-pointer-to-member-function-which-has-been-saved-in-a-vector-of-cust