How can I call my set my callback function from an object? - c++

Question

Here is some code:
typedef void (*ACallBack)(int i);
class SomeClass
{
private:
ACallBack aCallBack;
public:
void SetCallBack(ACallBack aCallBack);
};
void SomeClass::SetCallBack(ACallBack aCallBack)
{
this->aCallBack = aCallBack;
}
class SomeOtherClass
{
private:
SomeClass someClass;
public:
void InitializeSomeClass();
private:
void callBackMethod(int i);
};
void SomeOtherClass::InitializeSomeClass()
{
this->changeVariable = 10;
this->someClass.SetCallBack(this->callBackMethod); // DOESN'T WORK
this->someClass.UseCallBack();
}
void SomeOtherClass::callBackMethod(int i)
{
}
void globalCallBack(int i)
{
int myInt = i;
}
int main()
{
SomeClass sC;
sC.SetCallBack(globalCallBack); //WORKS!!
}
Basically if I try to set my callback function in SomeOtherClass it doesn't work but when I set it globally in main it does. What am I missing here?

Answer 1

Just use std::function and std::bind():
typedef std::function<void(int i)> ACallBack;
// old code pretty much the same
int main()
{
using namespace std::placeholders;
SomeClass sC;
sC.SetCallBack(globalCallBack); //WORKS!!
SomeOtherClass oC;
sC.SetCallBack(std::bind(&SomeOtherClass::callBackMethod,oC,_1)); //WORKS AS WELL!!
}
In this case you do not really need to pass void *userData but may add it as well if you need old code to compile.

Answer 2

You have to make the method static:
static void callBackMethod(int i, void* userData);
if you need a pointer to a method that is not static, ie an instance method, it becomes more complex.
typedef void ( myclass::*FUNC ) (int i, void* userData);
and if you want to use it, it becomes a hastlle :
myclass obj; // instantiate myclass
FUNC f = &myclass::myfunc; // assign address
( obj.*f ) ( 123, NULL ); // and call it