Qt: Custom derived class not declared in scope - c++

Question

Qt Newbie here experiencing a problem where it claims that I did not declare a class which I'm pretty sure is declared.
I cannot for the life of me figure this out. Please help.
Commenting out the problematic lines in Connection.h and .cpp results in compilable output.
Here is a slimmed down version of my code where the problem still exists:
Btw, Map.ui only has a Graphics View dragged into it.
Error message:
In file included from ../Map/Map.h:17:0,
from ../Map/City.cpp:1:
../Map/Connection.h:14:11: error: 'City' was not declared in this scope
QPair<City*, City*> cities;
^
../Map/Connection.h:14:18: error: 'City' was not declared in this scope
QPair<City*, City*> cities;
^
../Map/Connection.h:14:23: error: template argument 1 is invalid
QPair<City*, City*> cities;
^
../Map/Connection.h:14:23: error: template argument 2 is invalid
../Map/Connection.h:19:22: error: 'City' was not declared in this scope
Connection(QPair<City*, City*> cities, int cost);
^
../Map/Connection.h:19:29: error: 'City' was not declared in this scope
Connection(QPair<City*, City*> cities, int cost);
^
../Map/Connection.h:19:34: error: template argument 1 is invalid
Connection(QPair<City*, City*> cities, int cost);
Map.pro:
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = Map
TEMPLATE = app
SOURCES +=\
City.cpp \
Connection.cpp \
Map.cpp \
Driver.cpp
HEADERS += \
City.h \
Connection.h \
Map.h
FORMS += \
Map.ui
Map.h:
#ifndef MAP_H
#define MAP_H
#include <QApplication>
#include <QGraphicsItem>
#include <QMainWindow>
#include <QtCore>
#include <QtGui>
#include <QGraphicsScene>
#include <QGraphicsEllipseItem>
#include <QDebug>
#include <QPainter>
#include <QString>
#include <QVector>
#include "ui_Map.h"
#include "Connection.h"
#include "City.h"
namespace Ui
{
class Map;
}
class Map : public QMainWindow
{
Q_OBJECT
public:
explicit Map(QWidget *parent = 0);
~Map();
private:
Ui::Map *ui;
QGraphicsScene *scene;
};
#endif // MAP_H
Map.cpp:
#include "Map.h"
#include "ui_Map.h"
Map::Map(QWidget *parent) : QMainWindow(parent), ui(new Ui::Map)
{
ui->setupUi(this);
scene = new QGraphicsScene(this);
ui->graphicsView->setScene(scene);
City *c1 = new City(30, 30, 30, "K");
City *c2 = new City(30, 90, 30, "O");
Connection *conn1 = new Connection(45, 45, 45, 105, 1);
c1->setZValue(4);
c2->setZValue(4);
conn1->setZValue(2);
scene->addItem(c1);
scene->addItem(c2);
scene->addItem(conn1);
}
Map::~Map()
{
delete ui;
}
City.h:
#ifndef CITY_H
#define CITY_H
#include "Map.h"
class City : public QGraphicsItem
{
private:
int x;
int y;
int r;
QString name;
QRectF bounds;
QVector<QPair<City*, int> > neighbors;
public:
City();
City(int x, int y, int r, QString name);
int getX() { return this->x; }
int getY() { return this->y; }
int getR() { return this->r; }
QString getName() { return this->name; }
QVector<QPair<City*, int> > getNeighbors() { return this->neighbors; }
void setNeighbors(QVector<QPair<City*, int> >) { this->neighbors = neighbors; }
QRectF boundingRect() const;
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};
#endif // CITY_H
City.cpp:
#include "Map.h"
City::City()
{
this->bounds = QRectF(0, 0, 0, 0);
}
City::City(int x, int y, int r, QString name)
{
this->x = x;
this->y = y;
this->r = r;
this->name = name;
this->bounds = QRectF(x, y, r, r);
}
QRectF City::boundingRect() const
{
return QRectF(x, y, r, r);
}
void City::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QRectF rec;
if (this->bounds == QRectF(0, 0, 0, 0))
rec = boundingRect();
else
rec = this->bounds;
QBrush brush(Qt::blue);
QPen pen(Qt::blue);
painter->setBrush(brush);
painter->setPen(pen);
painter->drawEllipse(rec);
}
Connection.h:
#ifndef CONNECTION_H
#define CONNECTION_H
#include "Map.h"
class Connection : public QGraphicsItem
{
private:
int x1, x2;
int y1, y2;
int cost;
QRectF bounds;
QPair<City*, City*> cities; // PROBLEMATIC LINE -- CLAIMS CITY WAS NOT DECLARED
public:
Connection();
Connection(int x1, int y1, int x2, int y2, int cost);
Connection(QPair<City*, City*> cities, int cost); // PROBLEMATIC LINE -- CLAIMS CITY WAS NOT DECLARED
int getCost() { return this->cost; }
QRectF boundingRect() const;
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};
#endif // CONNECTION_H
Connection.cpp:
#include "Map.h"
Connection::Connection()
{
this->bounds = QRectF(0, 0, 0, 0);
}
Connection::Connection(int x1, int y1, int x2, int y2, int cost)
{
this->x1 = x1;
this->x2 = x2;
this->y1 = y1;
this->y2 = y2;
this->bounds = QRectF(x1, x2, y1, y2);
}
Connection::Connection(QPair<City*, City*> cities, int cost) // PROBLEMATIC BLOCK
{
int r = cities.first->getR();
this->x1 = cities.first->getX() + r/2;
this->x2 = cities.second->getX() + r/2;
this->y1 = cities.first->getY() + r/2;
this->y2 = cities.second->getY() + r/2;
this->cost = cost;
this->bounds = QRectF(x1, x2, y1, y2);
}
QRectF Connection::boundingRect() const
{
return QRectF(0, 0, 0, 0);
}
void Connection::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QRectF rec;
if (this->bounds == QRectF(0, 0, 0, 0))
rec = boundingRect();
else
rec = this->bounds;
QBrush brush(Qt::red);
QPen pen(Qt::red);
painter->setPen(pen);
painter->drawLine(QLine(this->x1, this->y1, this->x2, this->y2));
}
Driver.cpp:
#include "Map.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Map w;
w.show();
return a.exec();
}
Thank you for taking the time to look at this. I appreciate any feedback whatsoever. The problematic lines were compilable for a while but it seems that adding certain things "broke" it.
The answer to this thread got me thinking it might be something silly, but my attempts to change the order of things have not fixed it.

Answer 1

Just looking at the error message one can see that the City class is indeed not defined at Connection.
In file included from ../Map/Map.h:17:0,
from ../Map/City.cpp:1:
City.cpp starts out with a #include "Map.h" which is odd because there are no references to the Map type in the cpp file. City.cpp should start out with an #include "City.h".
City.h starts out with an #include "Map.h" which is even stranger because the City class make no mention of Map.
So at this point City.cpp:1 -> Map.h :17 you are including "Connection.h". At this point, there are no defined types. Not City, not Map. The compiler approaches the class Connection with no types defined.
Fixing it:
It is hard to guess how your dependencies actually look like but one solution for this particular include might be.
Start by including City.h first in your City.cpp. You should #include "X.h" for all X.cpp files.
Remove the #include "Map.h" from the City.h file.
If the Map type is required in City.cpp, include it.
The Connection.h obviously requires at least a forward declared class class City because of the pointers. So either do a forward declaration or an `#include "City.h"
In conclusion: Only include files in the header that your class actually requires. In the corresponding cpp, first include the header. Any type the header requires will also be required by the implementation. After that you include the additional types your implementation requires.