http://doc.qt.nokia.com/4.7/unix-signals.html

Apart from this, UNIX signal handlers must be ordinary C functions (in C++ you'll need the extern C linkage).

It's not possible to directly call a non static member function of class through C style signal handler. Try to delegate task of handling signal to an instance of class using a static member function. See code below for example:

@
#include <iostream>
#include <signal.h>

using namespace std;

class MyClass {
static MyClass* m;

public:

void handleSignal(int num){
cout<<"Signal handled: "<<num<<endl;
}

static void setSignalHandlerObject(MyClass* mc) {
m = mc;
}

static void callSignalHandler(int num){
m->handleSignal(num);
}
};

MyClass* MyClass::m = NULL;

int main(){
signal(SIGINT,MyClass::callSignalHandler);
while(1);
}
@

--

MainWindow::MainWindow(QWidget parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
struct sigaction action;
fd = open("/dev/hpi0",O_RDONLY);
memset(&action, 0, sizeof(action));
action.sa_handler = sigterm_handler;
action.sa_flags = 0;
sigaction(SIGIO, &action, NULL);
fcntl(fd, F_SETOWN, getpid());
fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | FASYNC);
}@
error at "action.sa_handler = sigterm_handler;"
message: error: argument of type 'void (MainWindow::)(int)' does not match 'void ()(int)'

(...)

@
void signalHandler(int signal)
{
//print incoming signal
switch(signal){
case SIGINT: fprintf(stderr, "SIGINT => "); break;
case SIGKILL: fprintf(stderr, "SIGKILL => "); break;
case SIGQUIT: fprintf(stderr, "SIGQUIT => "); break;
case SIGSTOP: fprintf(stderr, "SIGSTOP => "); break;
case SIGTERM: fprintf(stderr, "SIGTERM => "); break;
case SIGSEGV: fprintf(stderr, "SIGSEGV => "); break;
default: fprintf(stderr, "APPLICATION EXITING => "); break;
}

//...

}
@

Hope it helps!!

--