Class variable resets after function completes - c++

Question

I'm new to C++ from a java/python/etc background, and am trying to teach myself OO programming before I have to take a class on it next semester.
I'm trying to make an animation system using SFML, but am having some trouble with one of my class variables; it keeps resetting to 0 after I increment it. I'll start with the code and follow with a log output I'm using to help figure out what's going on.
SOLUTION: Being new to C++, I was an idiot and returned a new instance of my class in my getter functions; using [class]& func()... instead of [class] func() solved this, but now I have some refactoring to do.
Code (header):
...
typedef std::vector<Frame> frameVect; // (Frame defined above)
typedef std::vector<double> dubVect;
...
class limbAnim
{
private:
int limbNum;
int numFrames;
int curFrame;
frameVect frames;
public:
limbAnim(int limb, int nFrames, frameVect F);
<getters/setters>
void incCurFrame();
dubVect incrementAnimation(dubVect curPos, double curRot);
}
Code (cpp):
... (include vector, ofstream, etc)
std::ofstream AnimLog("log.log")
typedef std::vector<Frame> frameVect; // (Frame defined above)
typedef std::vector<double> dubVect;
...
limbAnim::limbAnim(int limb, int nFrames, frameVect F)
{
limbNum = limb;
curFrame = 0;
numFrames = nFrames;
frames = F;
}
void limbAnim::incCurFrame()
{
curFrame=curFrame+1;
if (curFrame >= numFrames)
{
curFrame = 0;
AnimLog << "Greater than." << std::endl;
}
}
dubVect limbAnim::incrementAnimation(dubVect curPos, double curRot)
{
AnimLog << limbNum << ", " << numFrames << std::endl;
if (numFrames > 0)
{
AnimLog << curFrame << std::endl;
dubVect curStepP = frames[curFrame].getStepPos();
double curStepR = frames[curFrame].getStepRot();
curPos[0] = curPos[0] + curStepP[0];
curPos[1] = curPos[1] + curStepP[1];
curRot = curRot + curStepR;
incCurFrame();
AnimLog << "Incremented: " << curFrame << std::endl;
}
dubVect retV = curPos;
retV.push_back(curRot);
return retV;
}
So, my log output looks good since I'm testing with 2 frames on limbs 6 & 8, except those limbs' curFrame seems to reset to 0 after incrementing:
...
5, 0
6, 2
0
Incremented: 1
7, 0
8, 2
0
Incremented: 1
9, 0
...
5, 0
6, 2
0
Incremented: 1
7, 0
8, 2
0
Incremented: 1
9, 0
...(ad nauseam)
Edit: Code calling the increment function.
(main.cpp)
// (Outside main loop.)
Animation walk_anim(12, "assets/anim/walk.dat");
// (Inside main loop.)
for (int i=0; i<12; i++)
{
dubVect animDat = walk_anim.getLimbFrame(i).incrementAnimation(limbPos[i], curDegs[i]);
dubVect newPos = getDVect(animDat[0], animDat[1]);
double newRot = animDat[2];
curDegs[i] = newRot;
if (curDegs[i] >= 360)
curDegs[i] -=360;
limbPos[i] = newPos;
}
getLimbFrame
Animation::Animation(int lNum, string fName)
{
numLimbs = lNum;
fileName = fName;
// Fill up limbVect with correct # of empty frames.
for (int i=0; i<numLimbs; i++)
{
frameVect emptyFVect;
limbAnim LA(i, 0, emptyFVect);
limbFrames.push_back(LA);
}
// Boring .dat parsing, populates the 'frames' var of each limbAnim.
loadAnim();
}
limbAnim Animation::getLimbFrame(int index)
{
if (index < numLimbs)
{
return limbFrames[index];
}
}

Answer 1

Hopefully you're aware that your functions take arguments by value, so they work on a copy of something.
You carefully avoided to show the really interesting code parts where you call incrementAnimation, most likely it follows the same bad pattern as the other functions.
I suggest reading up on how to pass objects by reference and const reference -- and how function arguments work in C++.

Answer 2

I think you need to declare that member variable, with the static keyword, then you can say it is a class variable, where it will be the shared for every instance of your class. Like this:
static int curFrame;
Then you need to initialize it from outside de class. Have in mind that declaration, is a lot different to initialization.
You can read about it here and here