C++ linker problems with static method

c++, linker, static-methods

Solution

You're missing this:

//VectorMath.cpp
#include "VectorMath.h"

             |
             V - here
Vector3D* VectorMath::norm(Vector3D* vector)
{
    ...
}

The `norm` function is part of `VectorMath::`. Without that, you just have a free function.

This is more about your design, but why are you using pointers to everything? This is much cleaner:

class VectorMath {
    public:
    static Vector3D norm(const Vector3D&);
};

Take references, you're in C++ so don't write C code. What happens when I call this?

VectorMath::norm(0); // null

It will either crash, you have to put in a check, in which case, what should it return? This is all cleaned up by using references.

Also, why not just make these members of the `Vector3D` class?

Vector3D* v = new Vector3D(x, y, z);
v->norm(); // normalize would be better, in my opinion

Lastly, stack-allocate things. Your code right now has a memory leak:

int main(void) {
    Vector3D* v = new Vector3D(x, y, z);
    Vector3D* normVector = VectorMath::norm(v); 

    // delete v;
    // ^ you're not deleting it!
}

Change it to this, and use RAII concepts:

int main(void) {
    Vector3D v(x, y, z);
    Vector3D* normVector = VectorMath::norm(v);

    // delete v;
    // ^ you're not deleting it!
}

And by making `norm` a member function you end up with the very clean code:

int main(void) {
    Vector3D v(x, y, z);
    Vector3D normVector(v.norm());
}

No pointers, no leaks, all sexy.

Problem

I'm writing a Vector3D class that calls a static method on a VectorMath class to perform a calculation. When I compile, I get this: ``` bash-3.1$ g++ VectorMath.cpp Vector3D.cpp /tmp/cc5cAPia.o: In function `main': Vector3D.cpp:(.text+0x4f7): undefined reference to 'VectorMath::norm(Vector3D*)' collect2: ld returned 1 exit status ``` The code: VectorMath.h: ``` #ifndef VECTOR3D_H #include "Vector3D.h" #endif class VectorMath { public: static Vector3D* calculatePerpendicularVector(Vector3D*, Vector3D*); static Vector3D* norm(Vector3D*); static double length(Vector3D*); }; ``` VectorMath.cpp ``` #include "VectorMath.h" Vector3D* norm(Vector3D* vector) { // can't be found by linker // do vector calculations return new Vector3D(xHead, yHead, zHead, xTail, yTail, zTail); } // other methods ``` Vector3D.cpp ``` #include "Vector3D.h" #include "VectorMath.h" // ... // vector implementation // ... int main(void) { Vector3D* v = new Vector3D(x, y, z); Vector3D* normVector = VectorMath::norm(v); // error here } ``` Why can't the linker find the `VectorMath::norm` method? At first glance I'd think that I'd need to declare norm like this: ``` Vector3D* VectorMath::norm(Vector3D* vector) { ``` but that doesn't help either...

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