please provide your linkedin. <3

Anyway, your error message implies to me you are using that QSvgGenerator Class, from whatever route, and I said:

If you are indeed using the QSvgGenerator Class, what did you do about the qmake: QT += svg from the doc page?

So try changing to first line to

QT += core gui svg

Clear out build output directory and try re-running qmake and rebuilding from scratch. Does that help?

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++11

You can make your code fail to compile if it uses deprecated APIs.

In order to do so, uncomment the following line.

#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0

SOURCES +=
../Source/array.cpp
../Source/button.cpp
../Source/class.cpp
../Source/constructor.cpp
../Source/container.cpp
../Source/function.cpp
../Source/functions.cpp
../Source/globals.cpp
../Source/variable.cpp
../Source/win_main.cpp
main.cpp

HEADERS +=
../Headers/array.h
../Headers/button.h
../Headers/class.h
../Headers/constructor.h
../Headers/container.h
../Headers/function.h
../Headers/functions.h
../Headers/globals.h
../Headers/variable.h
../Headers/win_main.h

FORMS +=

Default rules for deployment.

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

It looks like you are missing a library for this "SVG Generator", or possibly have not specified it correctly, or it's the wrong version/compiler, or other possibilities.

You need to state things like: what version of Qt, what platform, what compiler, where this SvgGenerator stuff is supposed to come from (is it the QSvgGenerator Class?), whether you build Qt yourself or got it from somewhere? And most important show your project's .pro file so we can see how you are trying to link?

If you are indeed using the QSvgGenerator Class, what did you do about the qmake: QT += svg from the doc page?

//Save file as SVG

QString path = QFileDialog::getSaveFileName(w,("Save as image"), "/demo.svg", ("SVG file (*.svg)"));

if (path.isEmpty())
    return;
temp_img.setFileName(path);

//temp_img.setViewBox(QRect(0, 0, 1000, 1000));

temp_img.setSize(QSize(2000, 2000));

I am trying to get Class Diagrams in svg format.

What does this mean? Something in a program of your own, something in Qt Creator, something else?

However, at run-time this error comes

So you are saying this this comes up at run-time (when you run your application), not at link time (during the build)?