[SOLVED] Unresolved External Symbol Error

[Paawan]

Hi All,

I am getting three errors when I try to pass an object to another class. The errors are:

film.obj:-1: error: LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __cdecl Film::metaObject(void)const " (?metaObject@Film@@UEBAPEBUQMetaObject@@XZ)

film.obj:-1: error: LNK2001: unresolved external symbol "public: virtual void * __cdecl Film::qt_metacast(char const *)" (?qt_metacast@Film@@UEAAPEAXPEBD@Z)

film.obj:-1: error: LNK2001: unresolved external symbol "public: virtual int __cdecl Film::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@Film@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z)

All have "File not found: film.obj" under the errors in red.

The class that I am trying to pass:

@class Film: public QObject
{
Q_OBJECT

Q_PROPERTY(QString title READ getTitle  WRITE setTitle)

Q_PROPERTY(QString director READ getDirector WRITE setDirector )
Q_PROPERTY(int duration READ getDuration WRITE setDuration )
Q_PROPERTY(QDate releaseDate READ getReleaseDate WRITE setReleaseDate)

public:
Film(); // Default constructor
Film(QString t,int dur, QString dir, QDate r ); // Constructor
void setTitle(QString t);
void setDuration (int dur);
void setDirector (QString dir);
void setReleaseDate (QDate r);

QString getTitle();
QString getDirector();
int getDuration();
QDate getReleaseDate();

private:
QString title;
int duration;
QString director;
QDate releaseDate;

};@

The class that has to receive it:

Header file:

@#include <QtCore>
#include <QTextStream>
#include <QFile>
#include <QString>
#include "film.h"

class FilmWriter
{

public:
FilmWriter();
FilmWriter(Film * myFilm);

private:

};
@

The CPP File:

@FilmWriter::FilmWriter(Film * myyFilm){

//Film myFilm(myyFilm);
QString mFileName = "F:/myFilms.txt"; //File to store the Films

QFile mFile(mFileName);

if (!mFile.open(QFile::WriteOnly | QFile::Text))

{
    qDebug()<< "Cannot open File";
    return;
}

QTextStream out(&mFile);



out<<myyFilm->getTitle();

out<<myyFilm->getDirector();

out<<myyFilm->getDuration();

out<<myyFilm->getReleaseDate().toString();

/*

out<< myFilm.getTitle();
out<< myFilm.getDirector();
out<< myFilm.getDuration();
out<<myFilm.getReleaseDate().toString();


*/

mFile.flush();
mFile.close();

}
@

Please help.

Thanks

[SGaist]

Hi,

Did you re-run qmake after adding Q_OBJECT to your Film class ?

[Paawan]

Sorted. Thanks for the help.

[SGaist]

You're welcome,

Don't forget to update the thread's title prepending solved so other forum users may know a solution has been found :)

[Lordon]

Hi, Im new in QT. Can you write more informations how to re-run qmake .
I have one more question. Is the qmake file the same as MyProject.pro ?? - the .pro file in my project ?

[mrjj]

@Lordon
Hi and welcome
Yes MyProject.pro is the qmake file.

• To re-run it means to go to build menu and select "Run qmake" to be sure.

In rare cases , you might also delete your build folder for things to be really remade.
To find build folder, look in "projects" tab, and its just Build directory.
This folder contains auto generated files and safe to delete all files in.
So you exploer to go there and delete all in those cases.

[Lordon]

Oh, my mistake. I forgot say, that Im working in VisualStudio. There is not something like "Run qmake". Is there any way to do this in Visual Studio ?

[mrjj]

Oh. I never used VS with Qt so Im not sure.

Normally you also install the Qt VS plugin that handles all this.

Since VS dont really use .pro files i assume you have this plugin as
you sound you can compile.

Did you install this plugin ?
http://doc.qt.io/vs-addin/
http://download.qt.io/official_releases/vsaddin/qt-vs-addin-1.2.5.exe.mirrorlist

If not, you will have that issue that Qt want a tool called moc.exe run on normal compiles.
This tools makes connect and a lot of other core features work.

If its not run, then you will see errors like in this thread.

What version of VS are you using ?
Make sure it all matches with version etc.

[KeithS]

@Lordon
You don't need to run qmake if using Visual Studio with the Qt VS plugin, as VS will set up custom build steps for your .ui files (to run uic) and .h files that use Q_OBJECT (to run moc).

[Xahon]

I have the same issue too, but with Visual Studio + Cmake setup.
There is something that cmake does about the moc:
[1/5] Automatic MOC and UIC for target MyProject
[2/5] Building CXX object Test05\CMakeFiles\MyProject.dir\MyProject_autogen\mocs_compilation.cpp.obj
[3/5] Building CXX object Test05\CMakeFiles\MyProject.dir\src\Main.cpp.obj
[4/5] Building CXX object Test05\CMakeFiles\MyProject.dir\src\MainWindow.cpp.obj
[5/5] Linking CXX executable bin\MyProject.exe
and the same errors in linking stage

In the build directory, after some searching, I found only a file called "mocs_compilation.cpp", but that file contains only

// This file is autogenerated. Changes will be overwritten.
// No files found that require moc or the moc files are included
enum some_compilers { need_more_than_nothing };

If I understand it correctly - moc should create an Q_OBJECT macro implementation for my class and that should be linked in final executable, but that file is not generated

UPD. A solution found
I also needed to add header files as source files in cmake add_library/add_executable functions, e.g. add_executable(MyProject "include/HeaderFileContaining_Q_OBJECT_Macro.hpp"). It seems weird because there is no need to "include" headers that way, it just doesn't make sense in non-qt cmake development