Undefined Reference Linker Error

nekkceb

I am getting the Undefined Reference Error in the linker step to my now sizeable project. Windows 11, Qt Ver 6.6.2 MinGW 64, Qt Creator ver 15.0.0-
I just added two new classes derived from QChart: Realtimeplot0 and MultSersPlot.
Here is the relevant items for Realtimeplot0:

#include <QChart>

#include "Macros.h"
#include <boost/circular_buffer.hpp>

class QGestureEvent;
class TDADataMap;
class QLineSeries;

class Realtimeplot0 : public QChart
{
private:
    Q_OBJECT
public:
    explicit Realtimeplot0(QGraphicsItem *parent = nullptr, Qt::WindowFlags wFlags = {});
...... (Lots of other declarations...)

    QColor &GetSeriesColor(int cc);

...... (Lots of protected and private stuff...)
};

In the .cpp file:

static QList<QColor> __rtpColors;
// Defined in the Constructor:
    __rtpColors << Qt::blue << Qt::red << Qt::yellow << Qt::green << Qt::magenta << Qt::black
                << Qt::darkGray;


QColor &GetSeriesColor(int cc)
{
    static QColor __rtrnClr = __rtpColors[0];
    int ndx = cc % __rtpColors.size();
    __rtrnClr = __rtpColors[ndx];
    return __rtrnClr;
}

Here is header to MuiltsersPlot:


class MultSersPlot : public Realtimeplot0
{
private:
    Q_OBJECT
public:
    MultSersPlot(QGraphicsItem *parent = nullptr, Qt::WindowFlags wFlags = {});

    void FinishPlot(TDADataMap *) override;

    void setAxisRange(QPointF minrng, QPointF maxrng, bool frc = false) override;

    void SetYVarData(int srsnr, int vnr);

};

And the Source file that generates the error (the only place currently where GetSeriesColor is invoked:

void MultSersPlot::SetYVarData(int srsnr, int vnr)
{
    QString srsName = QString("RealTime%1").arg(srsnr);
    switch (srsnr) {
    case 1:
        SetYVar1(vnr);
        break;
    case 2:
        SetYVar2(vnr);
        break;
    case 3:
        SetYVar3(vnr);
        break;
    case 4:
        SetYVar4(vnr);
        break;
    default:
        return;
    }

    if (m_data.size() < srsnr) {
        m_data.append(QList<QPointF>());
    } else {
        m_data[srsnr - 1].clear();
    }

    if (m_buffData.size() < srsnr) {
        m_buffData.append(boost::circular_buffer<QPointF>(GetBuffSz()));
    } else
        m_buffData[srsnr - 1].clear();
    if (m_plotSeries.size() < srsnr) {
        QLineSeries *realtimeseries = new QLineSeries;
        realtimeseries->setName(srsName);
        QColor srsClr = GetSeriesColor(srsnr);
        QPen srsPen;
        srsPen.setWidth(2);
        srsPen.setColor(srsClr);

        realtimeseries->setPen(srsPen);
        realtimeseries->setPointsVisible(true);
        QList<QAbstractAxis *> axs;
        axs = axes(Qt::Vertical, m_plotSeries[0]);
        realtimeseries->attachAxis(axs[0]);
        axs = axes(Qt::Horizontal, m_plotSeries[0]);
        realtimeseries->attachAxis(axs[0]);
        m_plotSeries.append(realtimeseries);
    }
}

The compile output (though I think the last are linker errors)

D:\kcbdev\bips_svn\CommonWidgets\CalEditFormBase.ui:-1: Warning: The name 'horizontalLayout' (QHBoxLayout) is already in use, defaulting to 'horizontalLayout1'.
D:\kcbdev\bips_svn\CommonWidgets\CalEditFormBase.ui:-1: Warning: The name 'gridLayout_8' (QGridLayout) is already in use, defaulting to 'gridLayout_81'.
D:\kcbdev\bips_svn\CommonWidgets\advProtocolDlgBase.ui:-1: Warning: The name 'gridLayout' (QGridLayout) is already in use, defaulting to 'gridLayout3'.
D:\kcbdev\bips_svn\CommonWidgets\advProtocolDlgMGABase.ui:-1: Warning: The name 'gridLayout' (QGridLayout) is already in use, defaulting to 'gridLayout3'.
D:\kcbdev\bips_svn\CommonWidgets\AWProtocolDlgBase.ui:-1: Warning: The name 'gridLayout' (QGridLayout) is already in use, defaulting to 'gridLayout1'.
D:\kcbdev\bips_svn\BIPS10\BIPSMain\BIPSMain.cpp:5: '#pragma message: In BIPSMain: Qt Version: 6.6.2'
D:/kcbdev/bips_svn/BIPS10/BIPSMain/BIPSMain.cpp:5:59: note: '#pragma message: In BIPSMain: Qt Version: 6.6.2'
    5 | #pragma message("In BIPSMain: Qt Version: " QT_VERSION_STR)
      |                                                           ^
:-1: error: CMakeFiles/BIPSMain.dir/D_/kcbdev/bips_svn/CommonWidgets/MultSersPlot.cpp.obj:MultSersPlot.c:(.bss+0x0): multiple definition of `savvmx'; CMakeFiles/BIPSMain.dir/D_/kcbdev/bips_svn/CommonWidgets/FVCalPlot.cpp.obj:FVCalPlot.cpp:(.bss+0x0): first defined here
:-1: error: CMakeFiles/BIPSMain.dir/D_/kcbdev/bips_svn/CommonWidgets/MultSersPlot.cpp.obj:MultSersPlot.c:(.bss+0x4): multiple definition of `savvmn'; CMakeFiles/BIPSMain.dir/D_/kcbdev/bips_svn/CommonWidgets/FVCalPlot.cpp.obj:FVCalPlot.cpp:(.bss+0x4): first defined here
:-1: error: CMakeFiles/BIPSMain.dir/D_/kcbdev/bips_svn/CommonWidgets/MultSersPlot.cpp.obj:MultSersPlot.c:(.text+0xe66): undefined reference to `Realtimeplot0::GetSeriesColor(int)'
:-1: error: collect2.exe: error: ld returned 1 exit status
:-1: error: ninja: build stopped: subcommand failed.

I have tried all sorts of solutions, none worked:
I moved the RealtimePlot.h and .cpp files to the top of my CMakeLists.txt file
I deleted the build folders to force Qt to start the build from scratch
I have run several 'Rebuild' operations from the QtCreator menu.
None work, I always get this error. The program worked fine until I recently added this new GetSeriesColor method.
Any help?

SGaist

Hi,

You declared that function in your class but you implemented it without the class scope in your .cpp file.

ChrisW67

@SGaist has addressed the last error message from your linker.

The two preceding error messages regarding savvmx and savvmn are probably because you have the storage for these allocated in a header file rather than a cpp file. Everywhere you include the header you get another instance of the same storage and symbol.

The use of names starting with double-underscore are reserved for the compiler implementation and should not be present in user code. It may work with a given toolchain but I would expect compiler warnings and portability will be degraded.
See 7.1.3 in ISO/IEC 9899:201x (draft)

nekkceb

@SGaist Well that is truly embarrassing! I guess it compiled OK because it did not use class-defined variables.

nekkceb

@ChrisW67 Thanks for that tip, I was not aware of that, in fact I use that for local non-class variables a lot! I guess I should back off. What is standard for naming non-class but file-local variables, or is that just bad practice?

ChrisW67

Any descriptive name that is not explicitly reserved should be fair. So defaultColors or _defaultColors would be OK; _DefaultColors or __defaultColors would not.

File-scoped variables can be declared static and become invisible outside the translation unit. Standard advice is to question the need for such variables and use an anonymous namespace instead of static:

namespace {
        QList<QColor> defaultColors  { 
                Qt::blue, Qt::red, Qt::yellow, Qt::green, 
                Qt::magenta, Qt::black, Qt::darkGray 
        };
};
// rest of file can see defaultColors

If your file-local color list is being populated in the constructor of a class then that strongly suggests it should be part of the class or initialised outside the class (as above).

__rtrnClr in GetSeriesColor seems to have no need to exist.
Are you sure the function needs a non-const reference return value and not just a QColor?