linking libraries

Hi,

I've used Qt for two days now, as I need it to make my final project (exam).

I am trying to link a library called "Vortex" to my Qt-project.

First I generate the Makefile;

qmake -o Makefile client

I've appended 'pkg-config vortex --cflags' to CFLAGS and CXXFLAGS in the Makefile;

CFLAGS = <previous flags>... 'pkg-config vortex --cflags'
CXXFLAGS = <previous flags>... 'pkg-config vortex --cflags'

and also added 'pkg-config vortex --libs' to the Makefile, in the LIBS section;

LIBS = <previous libs>... 'pkg-config vortex --libs'

Then I try to compile the code with "make".
This only results in an error message;

undefined reference to 'vortex_init()'

(vortex_init() is a function to initialize the Vortex library)

I have used #include <vortex.h> in source-file, client.cpp.




Am I perhaps linking the library the wrong way?

You should probably implement vortex_init() function yourself. Or is it contained in the library? Do you get other unresolved symbols too or is it the only one?

this is the only error, but it is also the only function I have in client.cpp for now.

/usr/local/include/vortex.h contains

gboolean vortex_init ();

I don't really know how to implement this function in my client.cpp file.. :confused:

Thanks for the answer! :)


output from compiler when running "make"

Code:

---

g++ -c -pipe -Wall -W -O2 -D_REENTRANT  -DQT_NO_DEBUG -DQT_THREAD_SUPPORT -DQT_SHARED -DQT_TABLET_SUPPORT `pkg-config vortex --cflags` -I/usr/share/qt3/mkspecs/default -I. -I/usr/include/qt3 -I.ui/ -I.moc/ -o .obj/client.o client.cpp
/usr/include/qt3/private/qucom_p.h:69: warning: ‘struct QUBuffer’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:77: warning: ‘struct QUType’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:104: warning: ‘struct QUType_Null’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:287: warning: ‘struct QUType_enum’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:307: warning: ‘struct QUType_ptr’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:326: warning: ‘struct QUType_iface’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:345: warning: ‘struct QUType_idisp’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:364: warning: ‘struct QUType_bool’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:383: warning: ‘struct QUType_int’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:403: warning: ‘struct QUType_double’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:423: warning: ‘struct QUType_charstar’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:444: warning: ‘struct QUType_QString’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucomextra_p.h:65: warning: ‘struct QUType_QVariant’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucomextra_p.h:87: warning: ‘struct QUType_varptr’ has virtual functions but non-virtual destructor
g++  -o client .obj/client.o    -L/usr/share/qt3/lib -L/usr/X11R6/lib -lqt-mt -lXext -lX11 -lm -lpthread `pkg-config vortex --libs`
.obj/client.o: In function `main':
client.cpp:(.text+0x2a6): undefined reference to `vortex_init()'
collect2: ld returned 1 exit status
make: *** [client] Error 1

---

this is what I would need to run in order to get client.o compiled the right way:

Code:

---

g++ -c -pipe -Wall -W -O2 -D_REENTRANT -DQT_NO_DEBUG -DQT_THREAD_SUPPORT -DQT_SHARED -DQT_TABLET_SUPPORT `pkg-config --libs vortex --cflags` -I/usr/share/qt3/mkspecs/default -I. -I/usr/include/qt3 -I.ui/ -I.moc/ -o .obj/client.o client.cpp

---

but that only generates more error messages;

Code:

---

g++: -lvortex: linker input file unused because linking not done
g++: -lgthread-2.0: linker input file unused because linking not done
g++: -lxml2: linker input file unused because linking not done
g++: -lz: linker input file unused because linking not done
g++: -lm: linker input file unused because linking not done
g++: -lglib-2.0: linker input file unused because linking not done

---

Have you used that library before? Isn't there some reference which tells you what needs to be done to use it?

yup, have used it before in an application not invloving Qt. That application works just fine to compile with the instructions given at;

http://www.aspl.es/fact/files/af-arc...ml#using_linux

i.e. compile the source file with

Code:

---

gcc `pkg-config --cflags --libs vortex` your-program.c -o your-program

---

I think the problem may have something to do with the fact that Qt firstly compile my client.cpp to .obj/client.o and secondly compile the .o file;

Code:

---

g++ <FLAGS..> -o .obj/client.o client.cpp
 
g++  -o client .obj/client.o <FLAGS...>

---

From Qt Designer docs:

Quote:

---

For example, qmake can configure the build process to take advantage of external libraries that are supported by pkg-config, such as the D-BUS and ogg libraries, with the following lines:
CONFIG += link_pkgconfig
PKGCONFIG += ogg dbus-1
More information about features can be found in the Adding New Configuration Features section of the qmake Advanced Usage chapter.

---

That solution is for Qt 4.x, and I'm using Qt 3.3.4. (I found it in the 4.x manual, but not in the 3.3 manual)

http://doc.trolltech.com/4.0/qmake-p...ation-features

I tried to use this solution in my Qt 3.3.4, but qmake just ignores it, and makes the Makefile as it would be without

CONFIG += link_pkgconfig
PKGCONFIG += vortex

(I added the lines above to client.pro, then run qmake -o Makefile client)

Perhaps an upgrade to 4.x will do it then. I will try to install it and try this out! I'll post comments about this later.

Could you show us what parameters get passed to the compiler in the linking stage?

Quote:

---

Originally Posted by JustaStudent

That solution is for Qt 4.x, and I'm using Qt 3.3.4. (I found it in the 4.x manual, but not in the 3.3 manual)

---

Here's the contents of $QTDIR/mkspecs/features/link_pkgconfig.prf file from Qt4:

Quote:

---

# handle pkg-config files
for(PKGCONFIG_LIB, $$list($$unique(PKGCONFIG))) {
QMAKE_CXXFLAGS += $$system(pkg-config --cflags $$PKGCONFIG_LIB)
LIBS += $$system(pkg-config --libs $$PKGCONFIG_LIB)
}

---

It should work with Qt3 also.

jacek, this solution works also for Qt 3.3.4. (with a little modification)

I edit /usr/share/qt3/mkspecs/default/qmake.conf (after making backup) and the lines

QMAKE_CFLAGS = -pipe

to

QMAKE_CFLAGS = -pipe `pkg-config vortex --cflags`

and

QMAKE_LIBS =

to

QMAKE_LIBS =`pkg-config vortex --libs`


save it, run qmake -o Makefile client again, and then make.

but still I get the same error message:

Code:

---

g++  -o client .obj/client.o    -L/usr/share/qt3/lib -L/usr/X11R6/lib `pkg-config vortex --libs` -lqt-mt -lXext -lX11 -lm -lpthread
.obj/client.o: In function `main':
client.cpp:(.text+0x2a6): undefined reference to `vortex_init()'
collect2: ld returned 1 exit status
make: *** [client] Error 1

---

wysota, what do you mean with 'parameters passed to the compiler in the linking stage'?
After above error, it stops compiling..

What does pkg-config vortex --libs return?

pkg-config vortex --libs
-pthread -L/usr/local/lib -lvortex -lgthread-2.0 -lxml2 -lz -lm -lglib-2.0

pkg-config vortex --cflags
-pthread -I/usr/local/include/vortex -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2


I'll wait with the install of Qt 4.1.1 until I know for sure it won't mess up my current configuration.

Quote:

---

Originally Posted by JustaStudent

I edit /usr/share/qt3/mkspecs/default/qmake.conf (after making backup) and the lines

---

It would be better if you would add:

Code:

---

QMAKE_CXXFLAGS += $$system(pkg-config --cflags vortex)
LIBS += $$system(pkg-config --libs vortex)

---

to your .pro file.

ok I restored my qmake.conf file and added

QMAKE_CXXFLAGS += $$system(pkg-config --cflags vortex)
LIBS += $$system(pkg-config --libs vortex)

to my .pro file

but still I get the same error message "undefined reference to vortex_init()"

Any ideas?

Have you run "make clean && qmake && make" after all these changes?

> more dummy.cpp

Code:

---

#include <qapplication.h>
#include <vortex.h>
 
int main( )
{
    vortex_init();
}

---

> more dummy.pro

Code:

---

TEMPLATE        = app
LANGUAGE        = C++
 
CONFIG  += qt warn_on release
 
SOURCES += dummy.cpp
 
FORMS   = form1.ui
 
QMAKE_CXXFLAGS += $$system(pkg-config --cflags vortex)
LIBS += $$system(pkg-config --libs vortex)
 
unix {
  UI_DIR = .ui
  MOC_DIR = .moc
  OBJECTS_DIR = .obj
}

---

> make clean && qmake && make

Code:

---

rm -f .obj/moc_form1.o
rm -f .moc/moc_form1.cpp
rm -f .ui/form1.cpp .ui/form1.h
rm -f .obj/dummy.o .obj/form1.o
rm -f *~ core *.core
/usr/share/qt3/bin/uic form1.ui -o .ui/form1.h
g++ -c -pipe -pthread -I/usr/local/include/vortex -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2 -Wall -W -O2 -D_REENTRANT  -DQT_NO_DEBUG -DQT_THREAD_SUPPORT -DQT_SHARED -DQT_TABLET_SUPPORT -I/usr/share/qt3/mkspecs/default -I. -I/usr/include/qt3 -I.ui/ -I. -I.moc/ -o .obj/dummy.o dummy.cpp
/usr/share/qt3/bin/uic form1.ui -i form1.h -o .ui/form1.cpp
g++ -c -pipe -pthread -I/usr/local/include/vortex -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2 -Wall -W -O2 -D_REENTRANT  -DQT_NO_DEBUG -DQT_THREAD_SUPPORT -DQT_SHARED -DQT_TABLET_SUPPORT -I/usr/share/qt3/mkspecs/default -I. -I/usr/include/qt3 -I.ui/ -I. -I.moc/ -o .obj/form1.o .ui/form1.cpp
/usr/include/qt3/qtooltip.h:86: warning: ‘class QToolTip’ has virtual functions but non-virtual destructor
/usr/share/qt3/bin/moc .ui/form1.h -o .moc/moc_form1.cpp
g++ -c -pipe -pthread -I/usr/local/include/vortex -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2 -Wall -W -O2 -D_REENTRANT  -DQT_NO_DEBUG -DQT_THREAD_SUPPORT -DQT_SHARED -DQT_TABLET_SUPPORT -I/usr/share/qt3/mkspecs/default -I. -I/usr/include/qt3 -I.ui/ -I. -I.moc/ -o .obj/moc_form1.o .moc/moc_form1.cpp
/usr/include/qt3/private/qucom_p.h:69: warning: ‘struct QUBuffer’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:77: warning: ‘struct QUType’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:104: warning: ‘struct QUType_Null’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:287: warning: ‘struct QUType_enum’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:307: warning: ‘struct QUType_ptr’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:326: warning: ‘struct QUType_iface’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:345: warning: ‘struct QUType_idisp’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:364: warning: ‘struct QUType_bool’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:383: warning: ‘struct QUType_int’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:403: warning: ‘struct QUType_double’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:423: warning: ‘struct QUType_charstar’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucom_p.h:444: warning: ‘struct QUType_QString’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucomextra_p.h:65: warning: ‘struct QUType_QVariant’ has virtual functions but non-virtual destructor
/usr/include/qt3/private/qucomextra_p.h:87: warning: ‘struct QUType_varptr’ has virtual functions but non-virtual destructor
g++  -o dummy .obj/dummy.o .obj/form1.o .obj/moc_form1.o   -L/usr/share/qt3/lib -L/usr/X11R6/lib -pthread -L/usr/local/lib -lvortex -lgthread-2.0 -lxml2 -lz -lglib-2.0 -lqt-mt -lXext -lX11 -lm -lpthread
.obj/dummy.o: In function `main':
dummy.cpp:(.text+0xd): undefined reference to `vortex_init()'
collect2: ld returned 1 exit status
make: *** [dummy] Error 1

---

Does it link when you remove #include <qapplication.h> and change:

Code:

---

CONFIG += qt warn_on release

---

to

Code:

---

CONFIG += warn_on release
CONFIG -= qt

---

?

Code:

---

// main.cpp
#include <vortex.h>
 
void main( ){
    vortex_init();
}

---

Code:

---

g++ main.cpp `pkg-config vortex --cflags --libs` -o test

---

Does this compile?

I found the problem! It is my bad actually, the Vortex library is a C library, not a C++ library.
So,

I changed the name of dummy.cpp to dummy.c,
I changed CXXFLAGS to CFLAGS in dummy.pro as below, then run

make clean && qmake && make.

Code compiled! I feel stupid that I did not realise this earlier! :o
Thank you for the troubleshooting!

> more dummy.c

Code:

---

#include <vortex.h>
 
int main( )
{
    vortex_init();
}

---

> more dummy.pro

Code:

---

TEMPLATE        = app
LANGUAGE        = C++
 
CONFIG  += qt warn_on release
 
SOURCES += dummy.c
 
LIBS += $$system(pkg-config --libs vortex)
 
QMAKE_CFLAGS += $$system(pkg-config --cflags vortex)
 
unix {
  UI_DIR = .ui
  MOC_DIR = .moc
  OBJECTS_DIR = .obj
}

---

> make clean && qmake && make

Code:

---

qmake -o Makefile dummy.pro
rm -f .obj/dummy.o
rm -f *~ core *.core
gcc -c -pipe -pthread -I/usr/local/include/vortex -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2 -Wall -W -O2 -D_REENTRANT  -DQT_NO_DEBUG -DQT_THREAD_SUPPORT -DQT_SHARED -DQT_TABLET_SUPPORT -I/usr/share/qt3/mkspecs/default -I. -I/usr/include/qt3 -I.ui/ -I.moc/ -o .obj/dummy.o dummy.c
dummy.c: In function ‘main’:
dummy.c:6: warning: control reaches end of non-void function
g++  -o dummy .obj/dummy.o    -L/usr/share/qt3/lib -L/usr/X11R6/lib -pthread -L/usr/local/lib -lvortex -lgthread-2.0 -lxml2 -lz -lglib-2.0 -lqt-mt -lXext -lX11 -lm -lpthread

---

Quote:

---

Originally Posted by JustaStudent

I found the problem! It is my bad actually, the Vortex library is a C library, not a C++ library.

---

Then you should use Vortex headers like this:

Code:

---

extern "C" {
#include <vortex.h>
};

---

Athough it's strange that Vortex authors didn't take care of it.