C++ "undefined reference to class::function" [duplicate] - c++

Question

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What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 9 years ago.
So far I've managed to fix my own errors, but this one is keeping me puzzled for a while now. If any of you have any hints, that would be greately appreciated! Thanks.
I'm using Eclipse on a Windows laptop, which gives me the following error after building:
undefined reference to `Point::Point()' circle.cpp
/Assignment4_1/IN4084MSc line 13 C/C++ Problem
All my files (main4_1.cpp, point.h, point.cpp, circle.h, circle.cpp) are part of a project (called Assignment4_1).
#include "point.h"
#include "circle.h"
#include <cmath>
using namespace std;
Circle::Circle(Point ct, double rd):Point(ct)
{
center = ct;
if(rd > 0)
{
radius = rd;
}
radius = -1;
}
Point Circle::get_center(){
return center;
}
double Circle::get_radius(){
return radius;
}
void Circle::print(){
cout << " <Circle(<Point(“"<<center.get_x()<<"”,“"<<center.get_y()<<"”)>,”"<<radius<<"”)>";
}
void Circle::print(string s){
cout << s;
print();
}
void Circle::println(){
print();
cout << endl;
}
void Circle::println(string s){
print(s);
cout << endl;
}
#ifndef CIRCLE_H_
#define CIRCLE_H_
#include <iostream>
#include "point.h"
using namespace std;
class Circle: public Point{
Point center;
double radius;
public:
Circle(Point ct, double rd);
Point get_center();
double get_radius();
void print();
void print(string s);
void println();
void println(string s);
};
#endif /* CIRCLE_H_ */
#include "point.h"
#include <cmath>
using namespace std;
Point::Point(double x, double y){
x_coord = x;
y_coord = y;
}
double Point::get_x(){
return x_coord;
}
double Point::get_y(){
return y_coord;
}
void Point::print(){
//post: has printed the contents of the Point object in the format
cout << "<Point( “ " << x_coord <<" ” , “ " << y_coord << " ” )>";
}
void Point::print(string s){
//post: has printed string s first, then printed the contents of the Point object
cout << s << " ";
print();
}
void Point::println(){
//post: has printed the contents of Point object, then moved the cursor to the next line
print();
cout << endl;
}
void Point::println(string s){
//post: has printed string s first, then printed the contents of the Point object, and moved the cursor to the next line
cout << s << " ";
println();
}
void Point::move(double dx, double dy){
// post: x_coord = x_coord + dx, y_coord = y_coord + dy
x_coord = x_coord + dx;
y_coord = y_coord + dy;
}
double Point::distance(Point that){
//post: returns the distance between this Point and that Point
return sqrt( pow(x_coord - that.get_x(),2) + pow(y_coord - that.get_y(),2) );
}
bool Point::equals(Point that){
//post : returns true if this Point and that Point have the same coordinates
return (x_coord = that.get_x());
}
#ifndef POINT_H_
#define POINT_H_
#include <iostream>
using namespace std;
class Point{
protected:
double x_coord;
double y_coord;
public:
Point(double x, double y);
Point();
double get_x();
double get_y();
void print();
void print(string s);
void println();
void println(string s);
void move(double dx, double dy);
double distance(Point that);
bool equals(Point that);
};
#endif /* POINT_H_ */
#include <iostream>
#include <cstdlib>
using namespace std;
#include "point.h"
#include "circle.h"
void test1(){
cout << "test1:" << endl;
Point p1 = Point(2,3);
cout << "Point p1 is created, the data of p1 = (2,3)" << endl;
cout << "p1.get_x() -> " << p1.get_x() << endl;
cout << "p1.get_y() -> " << p1.get_y() << endl << endl;
p1.println("p1.println() -> ");
cout << endl;
cout << "end test1" << endl << endl;
}
void test2(){
cout << "test2:" << endl;
cout << "Point p1 is created, the data of p1 = (2,3)" << endl;
cout << "Point p2 is created, the data of p2 = (0,0)" << endl;
Point p1 = Point(2,3);p1.println("p1.println() -> ");
Point p2 = Point(0,0);p2.println("p2.println() -> ");
cout << endl;
p1.println("p1 before move -> ");
cout << "p1.move(1,1)" << endl;p1.move(1,1);
p1.println("p1 after move -> ");
cout << endl;
cout << "p1.distance(p2) -> " << p1.distance(p2) << endl << endl;
cout << "p1.equals(p1) -> " << p1.equals(p1) << endl;
cout << "p1.equals(p2) -> " << p1.equals(p2) << endl;
cout << "end test2" << endl << endl;
}
int main(){
test1();
test2();
return 0;
}

Answer 1

The compiler is telling you to define
Point::Point()
which you have only declared in the Point class definition. A possible implementation would be to initialize both coordinates with 0.0:
Point::Point() : x_coord(0.0), y_coord(0.0) {}
You have to explicitly initialize the members in this case because built-in types do not get zero-initialized when default constructed.