Problem passing vector element

I have three classes.
Trial
Robot
WriteToFile

Trial is holding a pointer to a WriteToFile object and for a Robot object.

Trial is calling Robot method to return a string and passes it to his WriteToFile.

Robot is containing a private

Code:

vector<int> samplesRobotToKalmanFilter;

I initialized it using

Code:

samplesRobotToKalmanFilter.clear();

And the return method

Code:

const vector<int>& Robot::GetSamplesReadUsingRobot() const
{
        if(samplesRobotToKalmanFilter.empty())
               cout<<"empty\n";    //INDEED EMPTY
	return samplesRobotToKalmanFilter;
}

Inside this method I can see that samplesRobotToKalmanFilter is empty



WriteToFile has the following method

Code:

void WriteToExternalFile::WriteValuesToVector(const vector<int>& samplesvec, const vector<double>& valuesXY)
{
     if(samplesvec.empty())
               cout<<"empty\n";    //NOT SHOWING EMPTY
}

I call this last method from Trial instance:

Code:

writeinput->WriteValuesToVector(robot->GetSamplesReadUsingRobot() , robot->GetinputForKalmanFilter());

The problem: inside this last method samplesvec is no longer considered empty...

and does the argument robot->GetSamplesReadUsingRobot() output empty?

Originally Posted by Mario F.

and does the argument robot->GetSamplesReadUsingRobot() output empty?

Just checked; No, it is not empty. I guess that the problem is the output of this method

Code:

const vector<int>& Robot::GetSamplesReadUsingRobot() const
{
	return samplesRobotToKalmanFilter;
}

Inside the method samplesRobotToKalmanFilter is empty, but passing it by reference to another vector, the new vector is not considered empty.

How exactly is samplesRobotToKalmanFilter being initialized?

Please summarize the constructor and where is exactly is clear() being called.

Originally Posted by Mario F.

How exactly is samplesRobotToKalmanFilter being initialized?

Please summarize the constructor and where is exactly is clear() being called.

I run a clear method, right after it I call the method to return the vector and compare it to another. Then I check if the second vector is empty too.


I figured out that the problem is something about passing the vector by reference. I don't know the solution to the problem yet.

Is the Robot object that you get the values from still valid?

--
Mats

I figured out that the problem is something about passing the vector by reference. I don't know the solution to the problem yet.

I doubt it. When you pass by reference, you are not creating a copy of the object. If empty() is true for the original object, it should also be true for the reference.

What I suspect is that somewhere between you call clear() and Robot::GetSamplesReadUsingRobot() the object is being copied by value. Another option is that clear is never called.

You can test all of this by putting a break in the line clear() is called and start stepping through the code. If your app doesn't break, you know clear() is not being called.

EDITL: matsp also has a point