使用c ++函数指针作为信号处理程序。

Question

I'd like to add new handler to signal SIGUSR1 in my code. here's signal signature form header file signal.h :

void (*signal(int, void (*)(int)))(int);

My handler is a member function, so I'm using std::bind to make the function fit in signal accepted input.

myclass::my_handler(int x);

Here's my conversion of the member function to signal accepted input:

std::bind(&myclass::my_handler, this, std::placeholders::_1); 

However, std::bind return the c++ representation of function pointer (aka std::function<void(int)> ) and I need the C representation which is (void)(*)(int) .

Should I do the casting forcefully, or perhaps there's c++ alternative for signal ?

Thanks

Answer 1

There is no portable way to convert a C++ function to a C function because they can have different ABIs.

What you can do is this declare a global variable cpphandler as -

std::function<void(int)> cpphandler = NULL;

Also declare a function as -

extern "C" {
    void signal_handler(int i);
}
void signal_handler(int i){
    cpphandler(i);
    return;
}

Now in the function where you want to create the binding do -

cpphandler = std::bind(&myclass::my_handler, this, std::placeholders::_1); 
signal(x, signal_handler); //replace x with whatever signal you want to install 

This makes sure that the function signal_handler is created with C ABI. And calls the C++ function code with C++ ABI.

Now you can use the signal function with signal_handler .

Answer 2

As you are using a C++ compiler, I suggest that you simply define a normal function that calls your member function handler:

void signal_handler_wrapper(int x)
{
   myclass::my_handler(x);
}

Then in your main code:

signal(SIGINT, signal_handler_wrapper);