Basic question: Including headers with INCLUDEPATH doesn't work

Binary91

Hello together,

I'm working with QtCreator and for all my previous projects, I manually included libraries (headers & sources) by adding them these files to the project.

Well, I thought there should be an easier solution for that, because when I use pre-installed headers like QWidget.h or QApplication.h, I do not have to add these files to the project.

So I set an INCLUDEPATH to my project config file:

INCLUDEPATH += C:/Qt/projects/lib/headers \
                                   C./Qt/projects/lib/sources

and deleted the file attachments in the project.

By using INCLUDEPATH, QtCreator automatically autofills the name while I type it in my #include directive, BUT when I try to build/run the project, I get the following errors:
'undefined reference to vtable for "xxx"'
'undefined reference to vtable for "xxx"'
...

When I manually add the header files and the source files via project -> right mouse click --> add existing files, everything works fine again.

I think there should be a way to solve this without adding all those libraries manually to the project, because I also don't have to do this with the standard headers/sources from Qt...

Can someone help me with that?

Thank you in anticipation!
Binary

mrjj

Hi
'undefined reference to vtable for "xxx"'
often comes from lack of Q_OBJECT or not running qmake after adding it.
Are u sure its related to INCLUDEPATH ?
Remember to run qmake when changing .pro file

also , you show
C./Qt/projects/lib/sources
The DOT there is that typo and its : as it should ?

Also that seems to point to the CPP folder.

You only point INCLUDEPATH to .h files
You must still include the CPP files in the actual project OR
use the LIBS+= to point to any DLL/SO/LIB file produced.

as explained here
http://doc.qt.io/qtcreator/creator-project-qmake-libraries.html

Binary91

Hi and thank you for your post.

Yes, it should be ":" instead, that was not the problem.

You say, I still have to include the source files (cpp).

Two questions to that:

Why do I not have to include QWidget.cpp, QApplication.cpp and so on when including such standard headers?
Well, I did include the source files, set INCLUDEPATH to the directory where my header files are located, included them via #include directive in the source files (as I would do with a standard header file), built the project again and still get those errors.

When I follow thoses errors in QtCreator, I see that they all point to the corresponding source file, like for example:
project file:

INCLUDEPATH += C:/Qt/lib/headers

SOURCES += main.cpp \
libA.cpp \
libB.cpp

HEADERS += main.h

main.h:

#include <libA.h>
#include <libB.h>

libA.h

class test
{
  test();
  ~test();
};

libA.cpp

#include <libA.h>

test::test() // <-- error here
{
}

test::~test()  // <-- error here
{
}

As you can see, the problem is that including the header (path should be known because I set it with INCLUDEPATH) into its corresponding source file (which I manually included in my project file).

Can you imagine what's wrong with that?

mrjj

Hi

Why do I not have to include QWidget.cpp, QApplication.cpp and so on when including such standard headers?

You should not have to include any standard Qt cpp files. the .H is enough.
but if you write .pro file BY HAND make sure u include
TEMPLATE = app
and stuff like
QT += core gui
Else it wont link Qt to it!!

--

#include <libA.h>

test::test() // <-- error here
{
}

--

Is the file
libA.cpp IN THE SAME FOLDER as main.cpp ?

Binary91

@mrjj said in Basic question: Including headers with INCLUDEPATH doesn't work:

You should not have to include any standard Qt cpp files. the .H is enough.

Yeah but why do I have to with my own headers? Is there a list of pre-defined standard headers and their corresponding sources so compiler/linker knows that automatically? If yes, couldn't that list be extended by own headers/sources?

but if you write .pro file BY HAND make sure u include
TEMPLATE = app
and stuff like
QT += core gui
Else it wont link Qt to it!!

I do not create the whole project file by myself, QtCreator does that so all that stuff is included.

Is the file
libA.cpp IN THE SAME FOLDER as main.cpp ?

Nope, should it? I thought that exactly this could be avoided by setting an INCLUDEPATH, isn't it? I thought that after setting this path, the compiler/linker knows where to search for those headers, otherwise this INCLUDEPATH doesn't have any sense or am I missing something?

jsulm

@Binary91 said in Basic question: Including headers with INCLUDEPATH doesn't work:

error here

What is the error?
If it is something like "multiple definition" or "redefinition", then your header file probably does not contain "include guard", see here: https://en.wikipedia.org/wiki/Include_guard

jsulm

@Binary91 said in Basic question: Including headers with INCLUDEPATH doesn't work:

Yeah but why do I have to with my own headers?

Because those are yours and you have to care about them. How should the build system know?
You don't have to include any Qt cpp files simply because you link your application against already build Qt libraries.
If you add QT+= gui you tell qmake to link your application against QT GUI libraries.

Binary91

@jsulm said in Basic question: Including headers with INCLUDEPATH doesn't work:

@Binary91 said in Basic question: Including headers with INCLUDEPATH doesn't work:

Yeah but why do I have to with my own headers?

Because those are yours and you have to care about them. How should the build system know?
You don't have to include any Qt cpp files simply because you link your application against already build Qt libraries.
If you add QT+= gui you tell qmake to link your application against QT GUI libraries.

Ah that makes sense! So "gui" or "core" are libs that include the source code of the headers that I include? That sounds logically!

But I still do not know why my source files should be in the same directory as my headers when I use relative paths, because I set an INCLUDEPATH so compiler/linker should know where to search for it or am I wrong?

mrjj

@Binary91 said in Basic question: Including headers with INCLUDEPATH doesn't work:

Nope, should it?

Well it dont matter where it is, BUT you say it is in same folder!
So it cant find them and hence it dont like your test::test() as it never saw the .cpp file.

also INCLUDEPATH is for .H files and NOT .cpp files!

SOURCE is for .cpp files and iy MUST be correct path

like where where my xml lib is somewhere else
SOURCES += main.cpp
Configuration.cpp
Forms/AbstractForm.cpp \ <<<--------------- in a sub folder called Forms
Forms/ConfigurationForm.cpp
Forms/DefaultFormFooter.cpp \
../../Common/XML/pugixml-1.5/src/pugixml.cpp \

Look at the pugixml.cpp, here i tell it to go back 2 folders and into Common

So when you say

SOURCES += main.cpp \ CORRECT
libA.cpp \ WRONG. AS ITS NOT THERE
libB.cpp Also wrong ?

Binary91

@mrjj said in Basic question: Including headers with INCLUDEPATH doesn't work:

@Binary91 said in Basic question: Including headers with INCLUDEPATH doesn't work:

Nope, should it?

Well it dont matter where it is, BUT you say it is in same folder!
So it cant find them and hence it dont like your test::test() as it never saw the .cpp file.

also INCLUDEPATH is for .H files and NOT .cpp files!

SOURCE is for .cpp files and iy MUST be correct path

like where where my xml lib is somewhere else
SOURCES += main.cpp
Configuration.cpp
Forms/AbstractForm.cpp
Forms/ConfigurationForm.cpp
Forms/DefaultFormFooter.cpp \
../../Common/XML/pugixml-1.5/src/pugixml.cpp \

Look at the pugixml.cpp, here i tell it to go back 2 folders and into Common

So when you say

SOURCES += main.cpp \ CORRECT
libA.cpp \ WRONG. AS ITS NOT THERE
libB.cpp Also wrong ?

Yep I know that know and already fixed this. But I don't know why I have to set the full path of the header files after setting INCLUDEPATH?!

That is how my project file looks like now:

INCLUDEPATH += C:/Qt/lib/headers

SOURCES += main.cpp \
C:/Qt/lib/sources/libA.cpp \
C:/Qt/lib/sources/libB.cpp

HEADERS += main.h

It still throws these errors...
When I include those headers manually like I did with the sources, everything works fine. BUT I thought that I could avoid this with INCLUDEPATH...

mrjj

Well normally you do not need to do so...

INCLUDEPATH += ../../Common/CONET
../../Common/XML/pugixml-1.5/src/ \

the pugixml.h is in the src and i can just use
it like
#include "pugixml.h"

Binary91

@mrjj
What could cause that problems then? Do I have to change some build settings in QtCreator?

I mean, there is no error in the code, because after manually adding those headers to the project , like:

HEADERS += C:/Qt/lib/headers/libA.h

works without problems.
BUT something like this:

HEADERS += libA.h

also doesn't work!

I don't know what could be wrong. INCLUDEPATH does have an effect to QtCreator, because when I try to include one of my own headers, it searches and autofills the name of the header file. So QtCreator searches for those files in the INCLUDEPATH I set, but it can't combine them when trying to build the project...

mrjj

No, it works that way. pr default. Nothing I have seen in Creator adjust that.
Only thing that can go wrong is path is invalid ( on windows, spaces in path can be issue)

HEADERS += libA.h

Will work if the libA.h is in the same folder as the .pro file
Else its FALSE and will not work.

Binary91

@mrjj
I found out that the problem only appears to a few header files!

I include 3 headers, each declaring a subclass of a standard Qt class:

INCLUDEPATH += C:/Qt/lib/headers

HEADERS += main.h

SOURCES += main.cpp \
myQLineEdit.cpp \
myQPushButton.cpp \
myQString.cpp

The errors appear to the functions defined in the source files myQLineEdit.cpp and myQPushButton.cpp, but NOT in myQString.cpp!

I think I got the problem!! In myQLineEdit and myQPushButton class, I do have a Q_OBJECT. Can this cause the problems??

mrjj

Q_OBJECT is used by a tool called moc.exe to help make signals and slot possible
It should not to anything with regards to include files. :)
As far as I have ever seen.

Binary91

that is really annoying..
Why do those undefind reference errors appear to some of my source files but not to all of them?
Don't know where to search for an answer now

Binary91

By the way:
the problem really is Q_OBJECT...

I just wrote "Q_OBJECT" into the myQString class and look what happened: undefined reference vtable ... in myQString.cpp!

So Q_OBJECT makes the problems why I have to add all headers to the project! How can I avoid this?

mrjj

when u add Q_OBJECT, please run qmake!

Binary91

I already tried that.
Building, running
Building, qmake, running
qmake, running
qmake, building, running

None of the above ways succeded

mrjj

@Binary91
then please as last test
Complete delete the build folder.