Apple Mach-O Linker (Id) Error when making operator friend function in C++

Question

I'm fairly new to C++, so maybe I'm doing something wrong, but I cannot figure out what it is.

My assignment for a Data Structures class is to implement the following header file:

#ifndef __CS20A__Test__
#define __CS20A__Test__

#include <stdio.h>

namespace cs20a
{
class ThreeDPoint
{
public:
    ThreeDPoint(int x, int y, int z);

    double Distance() const;

    friend bool operator ==(const ThreeDPoint &pt1, const ThreeDPoint &pt2);
    friend bool operator !=(const ThreeDPoint &pt1, const ThreeDPoint &pt2);

    friend ThreeDPoint operator +(const ThreeDPoint& pt1, const ThreeDPoint& pt2);
    friend ThreeDPoint operator -(const ThreeDPoint& pt1, const ThreeDPoint& pt2);

    //dot product
    friend int operator *(const ThreeDPoint& pt1, const ThreeDPoint& pt2);

    int getX() const;
    int getY() const;
    int getZ() const;

private:
    int x;
    int y;
    int z;
};
}
#endif /* defined(__CS20A__Test__) */

Here's my implementation: #include "ThreeDPoint.h" #include #include

using namespace cs20a;

ThreeDPoint::ThreeDPoint(int x, int y, int z)
{
    this->x = x;
    this->y = y;
    this->z = z;
}

double ThreeDPoint::Distance() const
{
    return sqrt(pow(x, 2) + pow(y, 2) + pow(z, 2));
}

bool operator== (ThreeDPoint &pt1, ThreeDPoint &pt2)
{
    return ((pt1.getX() == pt2.getX()) && (pt1.getY() == pt2.getY()) && (pt1.getZ() == pt2.getZ()));
}
bool operator !=(const ThreeDPoint &pt1, const ThreeDPoint &pt2)
{
    return !(pt1.getX() == pt2.getX() && pt1.getY() == pt2.getY() && pt1.getZ() == pt2.getZ());
}

ThreeDPoint operator +(const ThreeDPoint& pt1, const ThreeDPoint& pt2)
{

    return ThreeDPoint(pt1.getX() + pt2.getX(), pt1.getY() + pt2.getY(), pt1.getZ() + pt2.getZ());
}
ThreeDPoint operator -(const ThreeDPoint& pt1, const ThreeDPoint& pt2)
{

    return ThreeDPoint(pt1.getX() - pt2.getX(), pt1.getY() - pt2.getY(), pt1.getZ() - pt2.getZ());
}

int operator *(const ThreeDPoint& pt1, const ThreeDPoint& pt2)
{
    return pt1.getX() * pt2.getX() + pt1.getY() * pt2.getY() + pt1.getZ() * pt2.getZ();
}

int ThreeDPoint::getX() const {
    return x;
}
int ThreeDPoint::getY() const {
    return y;
}
int ThreeDPoint::getZ() const {
    return z;
}

These two files in themselves compile fine, but when I add a driver like

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

int main(int argc, const char * argv[]) {
    cs20a::ThreeDPoint pt1(1,2,3);
    cs20a::ThreeDPoint pt2(1,2,3);

    // insert code here...
    std::cout << (pt1 == pt2);
    return 0;
}

Or any driver with ThreeDPoint == ThreeDPoint or ThreeDPoint + ThreeDPoint, When I try to build it, I get this error:

Ld /Users/jaredjensen/Library/Developer/Xcode/DerivedData/CS20A-fztpdusrphrftebtzmkhjpjcduym/Build/Products/Debug/CS20A normal x86_64
cd "/Users/jaredjensen/Google Drive/XCode/CS20A"
export MACOSX_DEPLOYMENT_TARGET=10.9    /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -L/Users/jaredjensen/Library/Developer/Xcode/DerivedData/CS20A-fztpdusrphrftebtzmkhjpjcduym/Build/Products/Debug -F/Users/jaredjensen/Library/Developer/Xcode/DerivedData/CS20A-fztpdusrphrftebtzmkhjpjcduym/Build/Products/Debug -filelist /Users/jaredjensen/Library/Developer/Xcode/DerivedData/CS20A-fztpdusrphrftebtzmkhjpjcduym/Build/Intermediates/CS20A.build/Debug/CS20A.build/Objects-normal/x86_64/CS20A.LinkFileList -mmacosx-version-min=10.9 -stdlib=libc++ -Xlinker -dependency_info -Xlinker /Users/jaredjensen/Library/Developer/Xcode/DerivedData/CS20A-fztpdusrphrftebtzmkhjpjcduym/Build/Intermediates/CS20A.build/Debug/CS20A.build/Objects-normal/x86_64/CS20A_dependency_info.dat -o /Users/jaredjensen/Library/Developer/Xcode/DerivedData/CS20A-fztpdusrphrftebtzmkhjpjcduym/Build/Products/Debug/CS20A

Undefined symbols for architecture x86_64:
"cs20a::operator==(cs20a::ThreeDPoint const&, cs20a::ThreeDPoint const&)", referenced from:
  _main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I've tried everything and I can't fix this error. This only happens when I make the operators friend functions. If I make them members, and delete one of the parameters, it works fine. Is there something I'm doing wrong?

See this question: http://stackoverflow.com/questions/10934226/class-friend-function-inside-a-namespace — xcvr, Jun 27 '15 at 17:46
I looked at that one, and added a forward declare in the header file but that didn't fix anything — jaredjxyz, Jun 27 '15 at 19:39
Did you add the `::` before operator? Like `friend bool ::operator ==(/*params*/)` in the friend declaration? — xcvr, Jun 27 '15 at 22:37

Quentin Perez · Accepted Answer · 2015-06-29T16:40:59.527

You forgot ThreeDPoint:: before operator in cpp file, and use binary operator instead of friend

/*.cpp add ThreaDproint before operator*/ 
bool ThreeDPoint::operator== (ThreeDPoint const & pt2)
{
    return ((this->x == pt2.getX()) && (this->y == pt2.getY()) && (this->z == pt2.getZ()));
}
bool ThreeDPoint::operator !=(const ThreeDPoint &pt2)
{
    return !(this->x == pt2.getX() && this->y == pt2.getY() && this->z == pt2.getZ());
    /* here you can do this 
    return !(this->operator==(pt2)); */
}

/* .h change friend for binary operator*/
bool operator ==(const ThreeDPoint &pt2);
bool operator !=(const ThreeDPoint &pt2);

EDIT: force use friend keyword

/* add cs20a:: before operator== */
bool cs20a::operator==(const ThreeDPoint &pt1, const ThreeDPoint &pt2)
{
     return (pt1.x == pt2.x && pt1.y == pt2.y && pt1.z == pt2.z);
}

Good luck :)

Thank you for answering. I see what you're saying, and that works, but my professor said we should be using the operators as friend functions. Is this possible? — jaredjxyz, Jun 28 '15 at 21:18

Apple Mach-O Linker (Id) Error when making operator friend function in C++

1 Answers1