Misunderstanding function pointer - passing it as an argument
I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole.
#include <iostream>
using namespace std;
class A{
public:
int dosomeA(int x){
cout<< "doing some A to "<<x <<endl;
return(0);
}
};
class B{
public:
B(int (*ptr)(int)){ptr(0);};
};
int main()
{
A a;
int (*AP开发者_运维知识库tr)(int)=&A::dosomeA;
B b(APtr);
return 0;
}
This brilliant piece of code leaves me with the compiler error:
cannot convert
int (A::*)(int)' to
int (*)(int)' in initialization
Firstly I want it to compile.
Secondly I don't want dosomeA to be STATIC.Pointers to members are different from normal function pointers. As the compiler error indicates the type of &A::dosomeA
is actually int (A::*)(int)
and not int (*)(int)
.
Inside B
's constructor you need an instance of A
to call the member on using one the .*
or ->*
operators.
E.g'
B(int(A::*ptr)(int))
{
A atmp;
(atmp.*ptr)(int);
}
http://www.parashift.com/c++-faq-lite/pointers-to-members.html
You don't have a pointer to a function that returns an int and takes an int. You have a pointer to a member-function that returns an int and takes an A* and an int. Not only do you need to fix the type of your pointer, B needs to provide an A* to serve as dosomeA's this
parameter.
Boost::bind has some functionality meant to simplify using function pointers in general, and they provide support for pointers to member functions. See here.
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