Pointer/Array and Struct Problems

[rookie]

Hello @all,
I am new to c++ so also to pointers/arrays and structs. I thought I understood them but now I've got some problems.

I'm about to write an OpenGL project with a 3D-Camera.
I used a struct for the cam and implemented some initialisation methods:

typedef struct Camera {
	float position[3];
	float upVector[3];
	float lookAtVector[3];
	float perpendicular[3];
} Camera;

float* crossProduct(float* v1, float* v2) {
	float result[3];
	result[0] = v1[1]*v2[2] - v1[2]*v2[1];
	result[1] = v1[2]*v2[0] - v1[0]*v2[2];
	result[2] = v1[0]*v2[1] - v1[1]*v2[0];
	return result;
}

void calculatePerpendicular(Camera *c) {
	Camera cam = *c;
	float* perpendicular = crossProduct(cam.upVector, cam.lookAtVector);
	cam.perpendicular[0] = perpendicular[0];
	cam.perpendicular[1] = perpendicular[1];
	cam.perpendicular[2] = perpendicular[2];
}

void initCamera(Camera cam) {
	//Camera cam = *c;
	cam.position[0] = 0.0f;
	cam.position[1] = 0.0f;
	cam.position[2] = 0.0f;

	cam.lookAtVector[0] = 0.0f;
	cam.lookAtVector[1] = 0.0f;
	cam.lookAtVector[2] = 1.0f;

	cam.upVector[0] = 0.0f;
	cam.upVector[1] = 1.0f;
	cam.upVector[2] = 0.0f;

	calculatePerpendicular(&cam);
}

now in my main.cpp I deklared the cam and wanted to initialize it but all values stay at their default value 0.0f

struct Camera cam;//global

initCamera(cam);//in main 

well I guess I just messed up something with the pointers because when I debugged

	cam.lookAtVector[0] = 0.0f;
	cam.lookAtVector[1] = 0.0f;
	cam.lookAtVector[2] = 1.0f;

worked but it wasnt save in the object i wanted to use in the prog. Also calculatePerpendicular(&cam); didn't work.

I wanted to learn these things so I used a camera object as parameter for initialisation and a pointer to the camera for the perpendicular.

I hope the problem is clear.

Greetings,
jan

[Darkmaster]

pass as reference, because this:

void initCamera(Camera cam) {
	//Camera cam = *c;
	cam.position[0] = 0.0f;
	cam.position[1] = 0.0f;
	cam.position[2] = 0.0f;

	cam.lookAtVector[0] = 0.0f;
	cam.lookAtVector[1] = 0.0f;
	cam.lookAtVector[2] = 1.0f;

	cam.upVector[0] = 0.0f;
	cam.upVector[1] = 1.0f;
	cam.upVector[2] = 0.0f;

	calculatePerpendicular(&cam);
}

does nothing.

[rookie]

yeah this was my first thought too as you can see in my comment :) but its just the same.
calculatePerpendicular(&cam); doesnt set the perpendicular either.

[Darkmaster]

you can also write it in the constructor

[S G H]

Do you know what "Pass as reference" Means? Because it's almost impossible that the results are the same.

[rookie]

well i used a reference here: calculatePerpendicular(&cam) didn't I?

u mean this right?

void initCamera(Camera *c) {
	Camera cam = *c;
	cam.position[0] = 0.0f;
	cam.position[1] = 0.0f;
	cam.position[2] = 0.0f;

	cam.lookAtVector[0] = 0.0f;
	cam.lookAtVector[1] = 0.0f;
	cam.lookAtVector[2] = 1.0f;

	cam.upVector[0] = 0.0f;
	cam.upVector[1] = 1.0f;
	cam.upVector[2] = 0.0f;

	calculatePerpendicular(c);
}

[rookie]

ah i thought 'Camera *c' is a reference to the cam but its actually 'Camera &c'

void calculatePerpendicular(Camera &c) {
	float* perpendicular = crossProduct(c.upVector, c.lookAtVector);
	c.perpendicular[0] = perpendicular[0];
	c.perpendicular[1] = perpendicular[1];
	c.perpendicular[2] = perpendicular[2];
}

void initCamera(Camera &c) {
	c.position[0] = 0.0f;
	c.position[1] = 0.0f;
	c.position[2] = 0.0f;

	c.lookAtVector[0] = 0.0f;
	c.lookAtVector[1] = 0.0f;
	c.lookAtVector[2] = 1.0f;

	c.upVector[0] = 0.0f;
	c.upVector[1] = 1.0f;
	c.upVector[2] = 0.0f;

	calculatePerpendicular(c);
}

ok solved this problem: Thanks Darkmaster and EssGeEich
finally better understanding of pointers :)

[S G H]

Yeah, the last example is the pass-by-reference.
The '*' simbol means passing a pointer.
Where there is none of them, it means passing by value.