4. C++ - Can't access function in another class

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C++ - Can't access function in another class


  • Hello,

    I've got a problems accessing a function in another class.
    Help would be appriciated.

    Regards

    Compiler: GNU GCC 5.3.0
    Qt Version: 5.11.2
    System: Windows 10 (10.0)

    Header file for the class to access:-

    class QG_CommandEdit: public QLineEdit {
    Q_OBJECT

public:
    QG_CommandEdit(QWidget* parent=0);
    virtual ~QG_CommandEdit()=default; //line 43 ****

    void readCommandFile(const QString& path);
    ... ...

    my.cpp file

    QString where = qApp->applicationDirPath().append("/").append(fileName); //this is valid

QG_CommandEdit inst;
inst.readCommandFile( where ); //line 222 ***

    errors:-
error: undefined reference to `vtable for QG_CommandEdit'                  - qg_commandedit.h #43
error: undefined reference to `QG_CommandEdit::QG_CommandEdit(QWidget*)'   - my.cpp #222
    0 1 Reply

  • @mad-hatter

    Is the associated source file included in the .pro file?

    0

  • @koahnig

    Is the associated source file included in the .pro file?

    Yes.

    0 1 Reply
  • Lifetime Qt Champion

    @mad-hatter please clean your project (worst case: delete build directory), run qmake and build again.

    1
  • Lifetime Qt Champion

    Hi,

    Usually, vtable related errors comes after you added or remove the Q_OBJECT macro. Either re-run qmake by hand or do as @aha_1980 suggested: nuke the build folder and re-build.

    2

  • Hello,

    Thanks for all your repies.

    Deleted build folder
    Deleted *.pro.usr
    Ran clean
    Ran Qmake
    Ran Rebuild

    Deleted build folder
    Deleted *.pro.usr
    Ran clean
    Ran Qmake
    Ran Build

    same errors,

    Is it something to do with virtual?
    virtual ~QG_CommandEdit()=default;

    Regards

    0
  • Lifetime Qt Champion

    Might be a silly question but did you implement your class constructor ?

    2

  • @SGaist
    A silly answer, I don't know about class constructors in this context.

    0 1 Reply
  • Qt Champions 2019

    @mad-hatter said in C++ - Can't access function in another class:

    I don't know about class constructors in this context

    Then you should learn.
    Do you have this in your cpp file:

    QG_CommandEdit::QG_CommandEdit(QWidget* parent=0)
{
}
    3

  • Hello,

    Thanks for your response.
    I can't change this file as its part of an open source project.

    @jsulm
    This is in the qg_commandedit.cpp file.

    QG_CommandEdit::QG_CommandEdit(QWidget* parent)
        : QLineEdit(parent)
        , keycode_mode(false)
        , relative_ray("none")
        , calculator_mode(false)

{
    setStyleSheet("selection-color: white; selection-background-color: green;");
    setFrame(false);
    setFocusPolicy(Qt::StrongFocus);
}

    Regards

    0 1 Reply

  • @mad-hatter

    Show the .pro or .pri file where the source "qg_commandedit.cpp" is included.

    0

  • @koahnig

    Pro file

    TEMPLATE = app

DISABLE_POSTSCRIPT = false

#uncomment to enable a Debugging menu entry for basic unit testing
#DEFINES += LC_DEBUGGING

DEFINES += DWGSUPPORT
DEFINES -= JWW_WRITE_SUPPORT

LC_VERSION="2.2.0-alpha"
VERSION=$${LC_VERSION}

# Store intermedia stuff somewhere else
GENERATED_DIR = ../../generated/librecad
# Use common project definitions.
include(../../common.pri)
include(./boost.pri)
include(./muparser.pri)

CONFIG += qt \
    warn_on \
    link_prl \
    verbose \
    depend_includepath

QT += widgets printsupport
CONFIG += c++11
*-g++ {
    QMAKE_CXXFLAGS += -fext-numeric-literals
}

GEN_LIB_DIR = ../../generated/lib
PRE_TARGETDEPS += $$GEN_LIB_DIR/libdxfrw.a \
		$$GEN_LIB_DIR/libjwwlib.a

DESTDIR = $${INSTALLDIR}

# Make translations at the end of the process
unix {
    LC_VERSION=$$system([ "$(which git)x" != "x" -a -d ../../.git ] && echo "$(git describe --tags)" || echo "$${LC_VERSION}")

    macx {
        TARGET = LibreCAD
        VERSION=$$system(echo "$${LC_VERSION}" | sed -e 's/\-.*//g')
        QMAKE_INFO_PLIST = Info.plist.app
        DEFINES += QC_APPDIR="\"LibreCAD\""
        ICON = ../res/main/librecad.icns
        contains(DISABLE_POSTSCRIPT, false) {
            QMAKE_POST_LINK = /bin/sh $$_PRO_FILE_PWD_/../../scripts/postprocess-osx.sh $$OUT_PWD/$${DESTDIR}/$${TARGET}.app/ $$[QT_INSTALL_BINS];
            QMAKE_POST_LINK += /usr/libexec/PlistBuddy -c \"Set :CFBundleGetInfoString string $${TARGET} $${LC_VERSION}\" $$OUT_PWD/$${DESTDIR}/$${TARGET}.app/Contents/Info.plist;
        }
    }
    else {
        TARGET = librecad
        DEFINES += QC_APPDIR="\"librecad\""
        RC_FILE = ../res/main/librecad.icns
        contains(DISABLE_POSTSCRIPT, false) {
            QMAKE_POST_LINK = cd $$_PRO_FILE_PWD_/../.. && scripts/postprocess-unix.sh
        }
    }
}
win32 {
    TARGET = LibreCAD
    DEFINES += QC_APPDIR="\"LibreCAD\""

    # add MSYSGIT_DIR = PathToGitBinFolder (without quotes) in custom.pro file, for commit hash in about dialog
    !isEmpty( MSYSGIT_DIR ) {
        LC_VERSION = $$system( \"$$MSYSGIT_DIR/git.exe\" describe --tags || echo "$${LC_VERSION}")
    }

    RC_FILE = ../res/main/librecad.rc
    contains(DISABLE_POSTSCRIPT, false) {
        QMAKE_POST_LINK = "$$_PRO_FILE_PWD_/../../scripts/postprocess-win.bat" $$LC_VERSION
    }
}

DEFINES += LC_VERSION=\"$$LC_VERSION\"

# Additional libraries to load
LIBS += -L../../generated/lib  \
    -ldxfrw \
    -ljwwlib

INCLUDEPATH += \
HEADERS += ui/lc_actionfactory.h \
    ....
    ui/qg_commandedit.h \
    ... 
SOURCES += ui/lc_actionfactory.cpp \
    ...
    ui/qg_commandedit.cpp \
    ...
    0
  • Moderators

    @mad-hatter said in C++ - Can't access function in another class:

    INCLUDEPATH +=
    HEADERS += ui/lc_actionfactory.h \

    Add a newline between these lines! Or rather, remove the INCLUDEPATH entirely.

    1

  • @sierdzio

    Thanks for your reply.
    I don't want to alter the pro file as it belongs to an open source project that works as it is.

    Regards

    0
  • Moderators

    It is a bug, at least tell them to fix it if you don't want to do it yourself. If a project is open source, by the way, you do have all the rights to do that modification on your own.

    4

  • Hello,

    @sierdzio

    INCLUDEPATH +=
    HEADERS += ui/lc_actionfactory.h \

    I'm sorry, ' INCLUDEPATH += ' should not be there, its a copy and paste error on my part.

    Regards

    0

  • Hello,

    I've changed the code and I am left with one error now.
    Is there something I should add in the header file?
    Help please!

    Regards

    QG_CommandEdit *inst = nullptr;
inst->QG_CommandEdit::readCommandFile( where ); //line 248

error: undefined reference to `QG_CommandEdit::readCommandFile(QString const&)' // line 248
    0 1 Reply
  • Lifetime Qt Champion

    Hi @mad-hatter

    Is there something I should add in the header file?

    That would help to resolve compile errors, when the compiler cannot find the definition of a function.

    Linker errors mean, the linker cannot find the implementation of the function.

    Usually this means either the implementation is missing in your source file or you have it in a source file that is not compiled/linked.

    Regards

    3
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