External Variables not transferring

[thinkingcow]

Hi, I'm trying to create a program that takes inputs from an external file "C:/Repo/GraphTestData.txt". This takes place in my main.cpp file, where it is parsed into two double QVectors x and y. Then, I externally export x and y to a shared header "data.h", where it gets accessed in another file named "networkplot.cpp". Here, I use QCustomPlot to plot the data onto a graph. However, the console says that data.h is not used directly by either of the cpp files. How can I fix this?

// data.h
#ifndef DATA_H
#define DATA_H

#include <QVector>

extern QVector<double> x;
extern QVector<double> y;

#endif // DATA_H

#ifndef NETWORKPLOT_H
#define NETWORKPLOT_H

#include <QMainWindow>
#include <QVector>
QT_BEGIN_NAMESPACE
namespace Ui { class networkplot; }
QT_END_NAMESPACE

class networkplot : public QMainWindow
{
    Q_OBJECT

public:
    networkplot(QWidget *parent = nullptr);
    ~networkplot();

private:
    Ui::networkplot *ui;
};
#endif // NETWORKPLOT_H

#include "networkplot.h"
#include "ui_networkplot.h"
#include <QDebug>
#include "data.h"

networkplot::networkplot(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::networkplot)
{
    ui->setupUi(this);
    extern QVector<double> x, y;
    /*QVector<double> x(100),y(100);
    for(int i=0;i<100;i++)
    {
        x[i] = i/50.0 - 1; // x goes from -1 to 1
        y[i] = x[i]*x[i]; // quadratic function
    }*/
    ui->customplot->addGraph();

    ui->customplot->graph(0)->setScatterStyle(QCPScatterStyle::ssDot);
    ui->customplot->graph()->setLineStyle(QCPGraph::lsLine);
    ui->customplot->xAxis->setLabel("X");
    ui->customplot->yAxis->setLabel("Y");
    ui->customplot->yAxis->setRange(-6000,100);
    ui->customplot->yAxis->setRange(-6000,8000);

    ui->customplot->setInteractions(QCP::iRangeDrag | QCP::iRangeZoom | QCP::iSelectPlottables);
    ui->customplot->graph(0)->setData(x,y);
    ui->customplot->rescaleAxes();
    ui->customplot->replot();
    ui->customplot->update();
}

networkplot::~networkplot()
{
    delete ui;
}

#include "networkplot.h"
#include <QApplication>
#include <QFile>
#include <QTextStream>
#include <QVector>
#include <QDebug>
#include "data.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    // File path
    QString filePath = "C:/Repo/GraphTestData.txt";

    // Vectors to store data
    QVector<double> x;
    QVector<double> y;

    // Open the file
    QFile file(filePath);
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
        qDebug() << "Error opening file:" << file.errorString();
        return -1;
    }

    // Read the file line by line
    QTextStream in(&file);
    while (!in.atEnd()) {
        // Read each line
        QString line = in.readLine();

        // Split the line into two doubles
        QStringList parts = line.split(" ");
        if (parts.size() == 2) {
            bool conversionX, conversionY;
            double numberX = parts[0].toDouble(&conversionX);
            double numberY = parts[1].toDouble(&conversionY);

            // Check if conversion was successful
            if (conversionX && conversionY) {
                // Append to vectors
                x.append(numberX);
                y.append(numberY);
            } else {
                qDebug() << "Error converting line to numbers:" << line;
            }
        } else {
            qDebug() << "Invalid line format:" << line;
        }
    }

    // Close the file
    file.close();

    // Print the content of vectors
    qDebug() << "Vector x:" << x;
    qDebug() << "Vector y:" << y;
    networkplot w;
    w.show();
    return a.exec();
}

It's my first time working with C++, so I would greatly appreciate some help!

[JonB]

@thinkingcow
I think you can find more information for the "fix available" by hovering over the warning message or clicking something.

Anyway, data.h declares that there are two global variables somewhere, x and y (btw really bad names for global variables).

But in fact no such global variables are actually defined anywhere in your code (might be in a data.cpp but you don't show any such file). And the 2 extern variables are not referenced anywhere. networkplot::networkplot has its own extern statement for them, main() defines an x & y but they are local variables, not globals.

You may be new to C++ but presumably not to C, else you would likely not know about extern. So the code question you have is really about C rather than C++.

Don't use any extern here, you don't need it. By the look of things, pass x & y as parameters from where they are defined in main() to your networkplot class instance. Probably as extra parameters to the constructor. Or via a separate method, plot(), which you call after construction that does just the ui->customplot->graph(0)->setData(x,y); part.