Question

I have a piece of code and some errors and warnings, I could not understand why they occur. Could you give me your advice?

The first:

#pragma once

#include "Vector3.h"
#include <vector>

#include <GL/glew.h>

class BoundingSphere
{
public:
    float radius;
    Vector3 center;
    BoundingSphere(float radius, Vector3 center) : radius(radius),center(center) {};
    BoundingSphere() {};
};

class TriangleFace;

class MeshVertex
{

private:
    Vector3 position; 
    std::vector<TriangleFace *> faces;
    Vector3 normal;
    bool normalUpdateNeeded;

public:

    unsigned int index;

    MeshVertex(void);
    MeshVertex(Vector3 position);
    ~MeshVertex(void);

    Vector3 &getPos() {return position;};
    void addFace(TriangleFace *face);
    const std::vector<TriangleFace*>& getFaces() {return faces;  };
    Vector3 getNormal();

    void setPos(Vector3 & pos) {position = pos; }
    bool isSurfaceParticle() {return faces.size()>0;}
    void updateNormal();
};

class TriangleFace
{
private:
    Vector3 normal;
    bool normalUpdateNeeded;

public:
    MeshVertex* particles[3];
    TriangleFace(void);
    TriangleFace(MeshVertex *p1, MeshVertex *p2, MeshVertex *p3);
    MeshVertex& operator[](int i) {  return *(particles[i]); }
    Vector3 getNormal();
    ~TriangleFace(void);
    void updateNormal();
};

class TriangleMesh
{
protected:
    std::vector<MeshVertex> particles;
    std::vector<TriangleFace> faces;

public:
    TriangleMesh(string filename);
    ~TriangleMesh(void);

    void reserveNumberOfFaces(unsigned int n) { faces.reserve(n); };
    void addFace(TriangleFace &f) {faces.push_back(f);};
    void addFace(MeshVertex *p1, MeshVertex *p2, MeshVertex *p3) {faces.push_back(TriangleFace(p1,p2,p3));};

    std::vector<TriangleFace>& getFaces() {return faces;};
    std::vector<MeshVertex>& getParticles() { return particles; };

    void updateNormals();

    BoundingSphere getBoundingSphere();
};


class RenderTriangleMesh
{
private: 
    TriangleMesh &m;

    GLuint vboid[2];

    GLfloat *vertices;
    GLfloat *normals;

public:
    RenderTriangleMesh(TriangleMesh &m);
    void draw();

private:
    void generateVBOs();
    void updateVBOs();

};

Errors:

error C2220: warning treated as error – no ‘object’ file generated

warning C4512: ‘RenderTriangleMesh’ : assignment operator could not be generated

And the other:

 virtual short SimpleAddOK(const GeneralMatrix* gm) { return 0; }

error :

error C2220: warning treated as error – no ‘object’ file generated

warning C4100: ‘gm’ : unreferenced formal parameter

Answer 1

The first is saying that the compiler could not generate an assignment operator. This happens because of your reference member, as references cannot be reseated:

struct foo
{
    int& i;
};

int x, y;
foo f = { x };
foo g = { y };

f = g; // ??? 

You can silence the warning by explicitly disabling it yourself:

struct foo
{
    int& i;

private:
    foo& operator=(const foo&); // declared but never defined
};

That’s an old trick to make the assignment operator unusable, but stops the compiler from generating it.

In C++11, you can do this:

struct foo
{
    int& i;

private:
    foo& operator=(const foo&) = delete;
};

which is more explicit and much less hacky.

---

The other is because you never used your argument, which can often be an error in program logic. You should probably remove its name if you don’t use it:

virtual short SimpleAddOK(const GeneralMatrix* /* gm */) { return 0; } 

Personally I delete it completely. Others do this:

virtual short SimpleAddOK(const GeneralMatrix* gm)
{
    (void)gm; // this "uses" gm

    return 0;
} 

It’s sometimes wrapped in a macro called USE:

#define USE(x) (void)x

virtual short SimpleAddOK(const GeneralMatrix* gm)
{
    USE(gm);

    return 0;
} 

I consider these inferior to simply deleting the name, because if the warning is actually correct (that is, you do have a flaw in your program and aren’t seeing it), you’re masking the warning, defeating the purpose.

Warnings should always be fixed, not silenced.