Complete example using Boost::Signals for C++ Eventing

The code below is a minimal working example of what you requested. ClassA emits two signals; SigA sends (and accepts) no parameters, SigB sends an int. ClassB has two functions which will output to cout when each function is called. In the example there is one instance of ClassA (a) and two of ClassB (b and b2). main is used to connect and fire the signals. It’s worth noting that ClassA and ClassB know nothing of each other (ie they’re not compile-time bound).

#include <boost/signal.hpp>
#include <boost/bind.hpp>
#include <iostream>

using namespace boost;
using namespace std;

struct ClassA
    signal<void ()>    SigA;
    signal<void (int)> SigB;

struct ClassB
    void PrintFoo()      { cout << "Foo" << endl; }
    void PrintInt(int i) { cout << "Bar: " << i << endl; }

int main()
    ClassA a;
    ClassB b, b2;

    a.SigA.connect(bind(&ClassB::PrintFoo, &b));
    a.SigB.connect(bind(&ClassB::PrintInt, &b,  _1));
    a.SigB.connect(bind(&ClassB::PrintInt, &b2, _1));


The output:

Bar: 4
Bar: 4

For brevity I’ve taken some shortcuts that you wouldn’t normally use in production code (in particular access control is lax and you’d normally ‘hide’ your signal registration behind a function like in KeithB’s example).

It seems that most of the difficulty in boost::signal is in getting used to using boost::bind. It is a bit mind-bending at first! For a trickier example you could also use bind to hook up ClassA::SigA with ClassB::PrintInt even though SigA does not emit an int:

a.SigA.connect(bind(&ClassB::PrintInt, &b, 10));

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