CODEWITHSUNDEEP
c++boostboost-signals2
Nicolas Mattia
Nicolas Mattia

Reputation: 1309

Connect pointer to boost::signals2

I was wondering if somehow it was possible to connect a pointer to a boost::signals2::signal. For my problem is the following : I want the object connected to the "signal" to be changed. For instance :

class Something
{
    public:
        int x;
        bool operator()(std::string str)
        {
            std::cout << str << x << std::endl;
            return true;
        }
};


int main()
{
    boost::signals2::signal<bool (std::string)> sig;
    Something something;
    something.x = 3;
    Something* somethingElse = new Something;
    somethingElse->x = 3;
    sig.connect(something);
    sig.connect(*somethingElse); 

    something.x = 2;
    somethingElse->x = 2;

    sig("x is : ");
}

The code will always output :

x is : 3

and I would like it to output

x is : 2

Now I feel like I am missing something, either an easy solution, or a good understanding of what the boost::signals2 are for.

Upvotes: 2

Views: 618

Answers (2)

sehe
sehe

Reputation: 393114

You just need to ref-wrap the functor you want to pass by reference (note that you will have to ensure the signal is disconnected before the functor goes out of scope).

Something something;
something.x = 3;

Something somethingElse;
somethingElse.x = 3;

sig.connect(something);
sig.connect(boost::ref(somethingElse)); 

something.x = 2;
somethingElse.x = 2;

sig("x is : ");

This will print

x is : 3
x is : 2

See it Live On Coliru

Upvotes: 4

dewaffled
dewaffled

Reputation: 2973

In c++ standard way to store objects is "by value". This means that a copy of the original value is created by holder to avoid dependency on lifetime of original value. If you need to store a pointer or reference to an object you should create a proxy holder with explicit reference capture and ensure that the reference will outlive holder. This is often accomplished with boost::bind which in c++11 is available as std::bind and the modern way is to use lambda functions with capture by reference. A good example of using bind with signals was given in this answer.

Upvotes: 0

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