class test : public QObject{
    Q_OBJECT
private:
...............................................
public:
    test();
public slots:
    void txt();
signals:
    void ok();
};

test::test(){
................................................
    connect(p, SIGNAL(clicked()), SIGNAL(ok()));
}

void test::txt(){
    l->setText("ok");
}

....................................................
test a, b;

QObject::connect(&a, SIGNAL(ok()), &b, SLOT(txt()));
QObject::connect(&b, SIGNAL(ok()), &a, SLOT(txt()));
....................................................

class test : public QObject{
    Q_OBJECT
private:
................................................
public:
    test();
public slots:
    void txt(QString);
signals:
    void ok(QString);
};

test::test(){
......................................................
    connect(p, SIGNAL(clicked()), SIGNAL(ok("word")));
}

void test::txt(QString s){
    l->setText("ok");
}

....................................................
test a, b;

QObject::connect(&a, SIGNAL(ok()), &b, SLOT(txt()));
QObject::connect(&b, SIGNAL(ok()), &a, SLOT(txt()));
....................................................

connect(p, SIGNAL(clicked()), SIGNAL(ok("word")));