QT，C ++无法在没有对象的情况下调用成员函数

Question

In my mainwindow.cpp is where call is made. Call is supposed to occur on button clicked event. Error says cannot call member function 'void Foo::setFooAttributes(A&, B&, C&, D&)' without object .

void MainWindow::on_generateButton_clicked()
{

  setCreator(ui->interfaceCreatorName->text());
  setAlternateName(ui->interfaceAlternateName->text());
  setDomain(ui->interfaceDomain->text().toInt());
  QString filename = getCreator() + "'s " + getAlternateName() + ".txt";
  QFile file( filename );
  A a; B b; C c; D d;
  Foo::setFooAttributes(a,b,c,d); //ERROR: cannot call member function without object
  generateTop(file);
  generateMiddle(file);
  generateSecondaryMid(file);
  generateLast(file);
  generateTertiaryMid(file, a, b, c, d);

}

The function itself looks like this:

void Foo::setFooAttributes(A &aFoo, B &bFoo, C &cFoo, D &dFoo){

   aFoo.stopPoint = MainWindow.ui->aInterfaceStopPoint->text().toDouble();
   aFoo.rate = MainWindow.ui->aInterfaceRate->text().toInt();
   aFoo.domain = MainWindow.ui->aInterfaceDomain->text().toInt();
   aFoo.length = MainWindow.ui->aInterfaceLength->text().toInt();

   bFoo.stopPoint = MainWindow.ui->bInterfaceStopPoint->text().toDouble();
   bFoo.rate = MainWindow.ui->bInterfaceRate->text().toInt();
   bFoo.domain = MainWindow.ui->bInterfaceDomain->text().toInt();
   bFoo.length = MainWindow.ui->bInterfaceLength->text().toInt();

   cFoo.stopPoint = MainWindow.ui->cInterfaceStopPoint->text().toDouble();
   cFoo.rate = MainWindow.ui->cInterfaceRate->text().toInt();
   cFoo.domain = MainWindow.ui->cInterfaceDomain->text().toInt();
   cFoo.length = MainWindow.ui->cInterfaceLength->text().toInt();

   dFoo.stopPoint = MainWindow.ui->dInterfaceStopPoint->text().toDouble();
   dFoo.rate = MainWindow.ui->dInterfaceRate->text().toInt();
   dFoo.domain = MainWindow.ui->dInterfaceDomain->text().toInt();
   dFoo.length = MainWindow.ui->dInterfaceLength->text().toInt();

}

I put the rest of code including foo.h in paste here pastebin source

I first tried calling setFooAttributes(a,b,c,d); without Foo:: but that gave me error like 'setFooAttributes' was not declared in this scope

Answer 1

Make your Foo::setFooAttributes a static member function, since it doesn't operate on a "this" instance.

While you're at it, if A/B/C/D are actually the same type (or a subtype of a common type), you might consider removing all the duplication, to better follow the DRY (Don't Repeat Yourself) principle:

template <typename A> static void Foo::setFooAttributes(Foo &aFoo, int iface) {

   aFoo.stopPoint = MainWindow.ui->interfaceStopPoint[iface]->text().toDouble();
   aFoo.rate = MainWindow.ui->interfaceRate[iface]->text().toInt();
   aFoo.domain = MainWindow.ui->interfaceDomain[iface]->text().toInt();
   aFoo.length = MainWindow.ui->interfaceLength[iface]->text().toInt();

}

static void Foo::setFooAttributes(Foo &aFoo, Foo &bFoo, Foo &cFoo, Foo &dFoo) {

    setFooAttributes(aFoo, 0);
    setFooAttributes(bFoo, 1);
    setFooAttributes(cFoo, 2);
    setFooAttributes(dFoo, 3);
}

(This would need you to convert each of {a,b,c,d}InterfaceStopPoint , {a,b,c,d}InterfaceRate , {a,b,c,d}InterfaceDomain and {a,b,c,d}InterfaceLength into arrays, instead of four individual variables).

You could even improve on this by using a loop or a variable-arity template function, but I'll leave that as an exercise.