error: expected class-name before '{' token { ^ - c++

Question

Hello I keep getting this
error: expected class-name before '{' token
{
^ line 15
what does this error mean exactly? Im attempting to inherit the controller class that has a function that I need to call in form1's cpp.
#ifndef FORM1_H
#define FORM1_H
#include <QDialog>
#include "controller.h"
namespace Ui {
class form1 ;
}
class form1 : public QDialog, public controller
{
Q_OBJECT
public:
explicit form1(QWidget *parent = 0);
~form1();
private slots:
void on_pushButton_clicked();
private:
Ui::form1 *ui;
};
#endif // FORM1_H
the controller class
#include "controller.h"
#include "ui_controller.h"
controller::controller(QWidget *parent) :
QWidget(parent),
ui(new Ui::controller) {
ui->setupUi(this);
show(1); }
void controller::show(int x) {
if(x==1)
{
myform1 = new form1(this);
myform1->show();
}
if(x==2)
{
myform2 = new form2(this);
myform2->show();
}
if(x==3)
{
myform3 = new form3(this);
myform3->show();
} }
controller::~controller() {
delete ui; }
controller.h:
#ifndef CONTROLLER_H
#define CONTROLLER_H
#include <QWidget>
#include <form1.h>
#include <form2.h>
#include <form3.h>
namespace Ui {
class controller;
}
class controller : public QWidget
{
Q_OBJECT
public:
form1 * myform1;
form2 * myform2;
form3 * myform3;
void show(int x);
explicit controller(QWidget *parent = 0);
~controller();
private:
Ui::controller *ui;
};
#endif // CONTROLLER_H

Answer 1

My guess is you have a circular include issue, meaning controller.h includes, either directly or indirectly, form1.h.
EDIT: Change the include I was talking about to a forward declaration - you don't need the full definition of form1:
#ifndef CONTROLLER_H
#define CONTROLLER_H
#include <QWidget>
class form1;
class form2;
class form3;
namespace Ui {
class controller;
}
class controller : public QWidget
{
//.................
//.................