beginner's question: simple class usage compiler error.

[yaraeovento]

I apologize for posting such a simple question, but after several tries, I am still confused.

Full disclosure: this is an exercise from "Sams Teach Yourself C++ in 24 Hours" by Jesse Liberty and Rogers Candenhead. This refers to Chapter 9 (Hour 9 Activity 1)

I created a class called Point, in Point.h

I created a class called Rectangle in Rectangle.h and Rectangle.cpp

If I create an int main() function in Rectangle.cpp (that includes Rectangle.h), I can compile Rectangle.cpp and run the resulting program. Fine.

Question:

I create a separate file called main.cpp. I include Rectangle.h. But now the compiler complains.

$ g++ main.cpp -o main
/tmp/cc38JIph.o: In function `main':
main.cpp:(.text+0x26): undefined reference to `Rectangle::Rectangle(int, int, int, int)'
main.cpp:(.text+0x32): undefined reference to `Rectangle::getArea() const'
collect2: ld returned 1 exit status

If I can create a class in Point.h and use it in Rectangle.h, why can I not just use Rectangle in main.cpp?

I am sure this is a very simple question, I deeply appreciate your pacience and help.

And the files, of course:


file: main.cpp

#include <iostream>
#include "Rectangle.h"

using std::cout;
using std::endl;

int main() {

  //intitialize a local Rectangle variable
  Rectangle myRectangle(100, 20, 50, 80);

  int area = myRectangle.getArea();

  std::cout << "Area: " << area << endl;
  std::cout << "Upper left X coordinate: " << myRectangle.getUpperLeft().getX() << endl;
  return 0;
}

file: Rectangle.h

#include "Point.h"

class Rectangle {
 public:

  Rectangle(int newTop, int newLeft, int newBottom, int newRight);
  ~Rectangle() {}

  int getTop() const {return top; }
  int getLeft() const {return left; }
  int getBottom() const {return bottom; }
  int getRight() const {return right; }

  Point getUpperLeft() const {return upperLeft; }
  Point getLowerLeft() const {return lowerLeft; }
  Point getUpperRight() const {return upperRight; }
  Point getLowerRight() const {return lowerRight; }

  void setUpperLeft(Point location);
  void setLowerLeft(Point location);
  void setUpperRight(Point location);
  void setLowerRight(Point location);

  void setTop(int newTop);
  void setLeft(int newLeft);
  void setBottom(int newBottom);
  void setRight(int newRight);

  int getArea() const;

 private:

  Point upperLeft;
  Point upperRight;
  Point lowerLeft;
  Point lowerRight;
  int top;
  int left;
  int bottom;
  int right;
};

file: Rectangle.cpp

#include "Rectangle.h"

Rectangle::Rectangle(int newTop, int newLeft, int newBottom, int newRight) {
  top = newTop;
  left = newLeft;
  bottom = newBottom;
  right = newRight;

  upperLeft.setX(left);
  upperLeft.setY(top);

  upperRight.setX(right);
  upperRight.setY(top);

  lowerLeft.setX(left);
  lowerRight.setY(bottom);

  lowerRight.setX(right);
  lowerRight.setY(bottom);
}


void Rectangle::setUpperLeft(Point location) {
  upperLeft = location;
  upperRight.setY(location.getY());
  lowerLeft.setX(location.getX());
  top = location.getY();
  left = location.getX();
}

void Rectangle::setLowerLeft(Point location) {
  lowerLeft = location;
  lowerRight.setY(location.getY());
  upperLeft.setX(location.getX());
  bottom = location.getY();
  left = location.getX();
}


void Rectangle::setLowerRight(Point location) {
  lowerRight = location;
  lowerLeft.setY(location.getY());
  upperRight.setX(location.getX());
  bottom = location.getY();
  right = location.getX();
}

void Rectangle::setUpperRight(Point location) {
  upperRight = location;
  upperLeft.setY(location.getY());
  lowerRight.setX(location.getX());
  top = location.getY();
  right = location.getX();
}

void Rectangle::setTop(int newTop) {
  top = newTop;
  upperLeft.setY(top);
  upperRight.setY(top);
}

void Rectangle::setLeft(int newLeft) {
  left = newLeft;
  upperLeft.setX(left);
  lowerLeft.setX(left);
}


void Rectangle::setBottom(int newBottom) {
  bottom = newBottom;
  lowerLeft.setY(bottom);
  lowerRight.setY(bottom);
}

void Rectangle::setRight(int newRight) {
  right = newRight;
  upperRight.setX(right);
  lowerRight.setX(right);
}


int Rectangle::getArea() const {
  int width = right - left;
  int height = top - bottom;
  return (width * height);
}

file: Point.h

class Point {
 public:

  //no constructor
  void setX(int newX) { x = newX; }
  void setY(int newY) { y = newY; }
  int getX() const {return x; }
  int getY() const {return y; }

 private:
  int x;
  int y;
};

[ZuK]

You have to add Rectangle.cpp to your project or compile like

g++ main.cpp Rectangle.cpp -o main

Kurt

[yaraeovento]

I see, sorry. I knew it must have been something stupid. Many thanks for taking the time and providing a reply so fast.

[Elysia]

No question is stupid. As long as you show that are willing and eager to put a little time to solve the problem yourself, you are more than welcome to post trivial questions you cannot grasp.
In fact, some may even like it when you do since it gives them something trivial to answer (and why do we answer, if not because we want?).