C++ Pointer function to other class function - c++

Question

I need help with passing a function pointer on C++. I can't linkage one function for a class to other function. I will explain. Anyway I will put a code resume of my program, it is much larger than the code expose here but for more easier I put only the part I need to it works fine.
I have one class (MainSystem) and inside I have an object pointer to the other class (ComCamera). The last class is a SocketServer, and I want when the socket received any data, it sends to the linkage function to MainSystem.
ComCamera is a resource Shared with more class and I need to associate the functions ComCamera::vRecvData to a MainSystem::vRecvData or other function of other class for the call when receive data and send de data to the function class associate.
Can Anyone help to me?
EDDITED - SOLUTION BELOW
main.cpp
#include <iostream>
#include <thread>
#include <string>
#include <vector>
#include <cmath>
#include <string.h>
#include <stdio.h>
#include <exception>
#include <unistd.h>
using std::string;
class ComCamera {
public:
std::function<void(int, std::string)> vRecvData;
void vLinkRecvFunction(std::function<void(int, std::string)> vCallBack) {
this->vRecvData = vCallBack;
}
void vCallFromCamera() {
this->vRecvData(4, "Example");
};
};
class MainSystem {
private:
ComCamera *xComCamera;
public:
MainSystem(ComCamera *xComCamera) {
this->xComCamera = xComCamera;
this->xComCamera->vLinkRecvFunction([this](int iChannelNumber, std::string sData) {vRecvData(iChannelNumber, sData); });
}
void vRecvData(int iNumber, string sData) {
std::cout << "RECV Data From Camera(" + std::to_string(iNumber) + "): " << sData << std::endl;
};
};
int main(void) {
ComCamera xComCamera;
MainSystem xMainSystem(&xComCamera);
xComCamera.vCallFromCamera();
return 0;
}
Output will be:
MainSystem RECV Data From Camera(4): Example

Answer 1

You can have ComCamera::vRecvData be of type std::function<void(int, std::string)> and then have ComCamera::vLinkRecvFunction() be like this:
void ComCamera::vLinkRecvFunction(std::function<void(int, std::string)> callBack)
{
this->vRecvData = callBack;
}
and have MainSystem constructor be like this:
MainSystem::MainSystem(ComCamera *xComCamera)
{
using namespace std::placeholders;
this->xComCamera = xComCamera;
this->xComCamera->vLinkRecvFunction([this](int iNumber, std::string sData){vRecvData(number, sData);});
}
Still though the original question has way too much code to go through friend.

Answer 2

Here what you want :
#include<iostream>
using std::cout;
class A; //forward declare A
class B{
public:
void (A::*ptr)(int x); //Only declare the pointer because A is not yet defined.
};
class A{
public:
void increase_by(int x){
a+=x;
} // this function will be pointed by B's ptr
int a = 0; // assume some data in a;
B b; // creating B inside of A;
void analyze(int y){
(*this.*(b.ptr))(y);
} // Some function that analyzes the data of A or B; Here this just increments A::a through B's ptr
};
int main(){
A a; // creates A
cout<<a.a<<"\n"; // shows initial value of a
a.b.ptr = &A::increase_by; // defines the ptr that lies inside of b which inturns lies inside a
a.analyze(3); // calls the initialize method
(a.*(a.b.ptr))(3); // directly calls b.ptr to change a.a
cout<<a.a; // shows the value after analyzing
return 0;
}
Output will be :
0
6
I still don't get why would you do something like this. But maybe this is what you wanted as per your comments.
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