getting value from another function and class c++

Question

Sorry guys I'm new to C++ and I have this silly question to ask. how to I retrieve the value of civIndex from LocationData computeCivIndex function to PointTwoD class. does the GET function help in this situation?

LocationData.h

class LocationData
{
  private:
    string sunType;
    int noOfEarthLikePlanets, noOfEarthLikeMoons;
    float aveParticulateDensity, avePlasmaDensity;
    static float civIndex;

  public:
    LocationData(); //default constructor

    LocationData(string, int, int, float, float); // no default constructor
    void setLocationData(string, int, int, float, float);
    void displaydata();


    static float computeCivIndex(string st, int earth, int moons, float particle, float plasma);

};

locationdataimp.cpp

float LocationData::civIndex = 0;

//convert sunType to sunTypePercentage
float LocationData::computeCivIndex(string st, int earth, int moons, float particle, float plasma)
{

    float sunTypePercent;

    if(st == "Type 0")
    {
        sunTypePercent = 80.0;
    }
    else if(st == "Type B")
    {
        sunTypePercent = 45.0;
    }
    else if(st == "Type A")
    {
        sunTypePercent = 60.0;
    }
    else if(st == "Type F")
    {
        sunTypePercent = 75.0;
    }
    else if(st == "Type G")
    {
        sunTypePercent = 90.0;
    }
    else if(st == "Type K")
    {
        sunTypePercent = 80.0;
    }
    else if(st == "Type M")
    {
        sunTypePercent = 70.0;
    }

    // calculate CIV Value
    float civNum,civNum1,civNum2,civNum3,civNum4,civNum5;

    civNum1 = sunTypePercent / 100;
    civNum2 = plasma + particle;
    civNum3 = civNum2 / 200;
    civNum4 = civNum1 - civNum3;
    civNum5 = earth + moons;

    civNum = civNum4 * civNum5;

    civIndex = civNum;
    //return civNum;
}

pointtwod.h file

class PointTwoD
{
private:
    int xcord,ycord;
    float civIndex;
    LocationData locationdata;

public:
        PointTwoD();

        PointTwoD(int, int, string, int, int, float, float, float);

    string toString();

    void displayPointdata();        

};

pointtwod.cpp

void PointTwoD::displayPointdata()
{
    PointTwoD pointtwod;
    LocationData locationdata;
    cout << "X axis: " << xcord << endl;
    cout << "Y axis: " << ycord << endl;
    cout << "civ: " << locationdata.civIndex  << endl;
    //locationdata.displaydata();
}

so what should i include or what mistake have i made?

Answer 1

The declaration of static float LocationData::civIndex; means that civIndex is static and private(*) in LocationData.

(*) as the default access modifier

The private access means that you cannot access it directly via a variable of type LocationData if that class does not explicitly allow it. You have two options:

1) Provide a public getter function:

public static float LocationData::getCivIndex()
{
  return civIndex;
}

Note: you will need to declare this function in the class definition as well:

class LocationData
{
  // ...
  public static float getCivIndex();
};

2) Make the access of civIndex in LocationData public.

The second option is not advised as that would allow any code to directly access and modify the value of civIndex, which can easily lead to errors (and errors of these types are hard to track down in a large project). Even if you need a setter function that only sets the passed-in value, it is advisable to declare the variable private as that forces other code to go through the public method, making it easier to identify what code is accessing the variable during debugging in case of an error.

You can use option 1) like this:

LocationData locationData;
locationdata.getCivIndex();

Or even without having a variable of type LocationData, as the variable is static in that class:

LocationData::getCivIndex();

Answer 2

You can not directly access locationdata.civIndex like you did. Why? Because you set civIndex as a private member of the LocationData class.

There are a few solutions depending on your needs:

Make civIndex a public member of LocationData

or

Create a getter method to provide civIndex such as

  static float getCivIndex( )
  {
      return civIndex;
  }

See:

C++ Public

C++ Protected

C++ Private

Answer 3

computeCivIndex is a static member, so the correct syntax is:

cout << "civ: " << LocationData::civindex << endl;

However, your civindex variable is private, so you have to create a getter:

static float getCivIndex()
{
    return civIndex;
}

cout << "civ: " << LocationData::getCivIndex() << endl;