Question

i get 2 linker errors when trying to compile my program which includes these two files (causing the problem, in particular the lines in bold)

and i’m new to C++ so excuse my ignorance.

Assignment1.obj : error LNK2001: unresolved external symbol “public: class Vector __thiscall Vector::operator^(class Vector)” (??TVector@@QAE?AV0@V0@@Z)

1>Assignment1.obj : error LNK2001: unresolved external symbol “class std::basic_ostream > & __cdecl operator<<(class std::basic_ostream > &,class Point)” (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@VPoint@@@Z)

1>c:……\visual studio 2010\Projects\Assignment1\Release\Assignment1.exe : fatal error LNK1120: 2 unresolved externals

point.h file:

#ifndef SS_Point_H
#define SS_Point_H

#include "common.h"

//==================================================================
//  Point Class Definition
//==================================================================

class Point {
friend class Vector;
protected:
 int dimn;            // # coords (1, 2, or 3 max here)
 Error err;           // error indicator
public:
 double x, y, z;      // z=0 for 2D, y=z=0 for 1D

 //----------------------------------------------------------
 // Lots of Constructors (add more as needed)
 Point() { dimn=3; x=y=z=0; err=Enot; }
 // 1D Point
 Point( int a) {
  dimn=1; x=a; y=z=0; err=Enot; }
 Point( double a) {
  dimn=1; x=a; y=z=0; err=Enot; }
 // 2D Point
 Point( int a, int b) {
  dimn=2; x=a; y=b; z=0; err=Enot; }
 Point( double a, double b) {
  dimn=2; x=a; y=b; z=0; err=Enot; }
 // 3D Point
 Point( int a, int b, int c) {
  dimn=3; x=a; y=b; z=c; err=Enot; }
 Point( double a, double b, double c) {
  dimn=3; x=a; y=b; z=c; err=Enot; }
 // n-dim Point
 Point( int n, int a[]);
 Point( int n, double a[]);
 // Destructor
 ~Point() {};

 //----------------------------------------------------------
 // Input/Output streams
 **friend std::istream& operator>> ( std::istream&, Point&);
 friend std::ostream& operator<< ( std::ostream&, Point );**

….}

while point.c file:

#include "point.h"
#include "vector.h"
#include <iostream.h>
//==================================================================
// Point Class Methods
//==================================================================

//------------------------------------------------------------------
// Constructors (add more as needed)
//------------------------------------------------------------------

// n-dim Point
Point::Point( int n, int a[]) {
 x = y = z = 0;
 err = Enot;
 switch (dimn = n) {
 case 3: z = a[2];
 case 2: y = a[1];
 case 1: x = a[0];
  break;
 default:
  err=Edim;
 }
}

Point::Point( int n, double a[]) {
 x = y = z = 0.0;
 err = Enot;
 switch (dimn = n) {
 case 3: z = a[2];
 case 2: y = a[1];
 case 1: x = a[0];
  break;
 default:
  err=Edim;
 }
}

//------------------------------------------------------------------
// IO streams
//------------------------------------------------------------------

// Read input Point format: "(%f)", "(%f, %f)", or "(%f, %f, %f)"


**std::istream& operator>>( std::istream& input, Point& P) {**
     char c;
     input >> c;                // skip '('
     input >> P.x;
     input >> c;                
     if (c == ')') {
      P.setdim(1);       // 1D coord
      return input;
     }
     // else                    // skip ','
     input >> P.y;
     input >> c;
     if (c == ')') {
      P.setdim(2);       // 2D coord
      return input;
     }
     // else                    // skip ','
     input >> P.z;
     P.setdim(3);               // 3D coord
     input >> c;                // skip ')'
     return input;
    }

// Write output Point in format: "(%f)", "(%f, %f)", or "(%f, %f, %f)"
**std::ostream& operator<<( std::ostream& output, Point P) {**
 switch (P.dim()) {
 case 1:
  output << "(" << P.x << ")";
  break;
 case 2:
  output << "(" << P.x << ", " << P.y << ")";
  break;
 case 3:
  output << "(" << P.x << ", " << P.y << ", " << P.z << ")";
  break;
 default:
  output << "Error: P.dim = " << P.dim();
 }
 return output;
}

…..
…..
…..
}

Answer 1

Its hard from the information given to see the problem; you have C++ code in a .c file, but presumably your compiler would complain if you hadn’t got it to recognize that. To avoid doubt, rename your point.c file point.cpp.

Generally, its a good idea to use forward declarations of things you want to be friends; this ensures you are befriending some top-level function and not some inner function (particularly regards to friend classes).

// forward declarations
class Point;
std::istream& operator>> ( std::istream&, Point&);
std::ostream& operator<< ( std::ostream&, Point );

// point class
class Point {
   ...
   friend std::istream& operator>> ( std::istream&, Point&);
   friend std::ostream& operator<< ( std::ostream&, Point );
   ...