Qt5 Compile with an error "undefined reference" when linking static libraries or dynamic libraries

[Alex_wang]

Qt5 linked the static libraries which have defined by this function,but the error still appear:

qt_odin.o：‘QOdinMsg::MsgQCreate()’ ：
qt_odin.cpp.text+0x14)：function ‘od_msg_create_fix_trans(char const*, unsigned int, unsigned int, unsigned int) ’  undefined reference

linked lib：

LIBS += $$PWD/interface/lib/tx1/libparam_msg.a  \
             $$PWD/interface/lib/tx1/libengine.a  \
             $$PWD/interface/open_lib/json-c-0.12.1/tx1/lib/libjson-c.a

nm：

nm libengine.a | grep od_msg_create_fix_trans:
0000000000000000 T od_msg_create_fix_trans

Regards

[koahnig]

@Alex_wang

Did you check the signatures of paramters?

What is the tool chain you are using?

[Alex_wang]

the compiler cmd :

/home/suma/tx1/gcc/gcc-linaro-6.2.1-2016.11-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-g++ 
-Wl,-rpath-link,/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib/aarch64-linux-gnu 
-Wl,-rpath-link,/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib/aarch64-linux-gnu/tegra 
-Wl,-rpath-link,/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib 
-Wl,-rpath-link,/home/suma/tx1/Linux_for_Tegra/rootfs/lib/aarch64-linux-gnu 
--sysroot=/home/suma/tx1/Linux_for_Tegra/rootfs
 -Wl,-O1 -Wl,-rpath,/usr/local/qt5/lib 
-o GUIControlSystem 
main.o ... ...  qt_odin.o qrc_qml.o ... ... moc_qt_odin.o   
-L/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib/aarch64-linux-gnu 
-L/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib 
-L/home/suma/tx1/Linux_for_Tegra/rootfs/lib/aarch64-linux-gnu 
/home/suma/interface/lib/tx1/libparam_msg.a 
/home/suma/interface/lib/tx1/libengine.a 
/home/suma/interface/open_lib/json-c-0.12.1/tx1/lib/libjson-c.a 
-L/home/suma/tx1/qt/qt5/lib 
-lQt5QuickWidgets -lQt5Quick -lQt5Widgets -lQt5Multimedia -lQt5Gui -lQt5Qml 
-lQt5Network -lQt5Sql -lQt5SerialPort -lQt5Core -lGLESv2 
-lpthread 

[Alex_wang]

@koahnig
hi,
the tool chain is aarch64-linux-gnu-g++ (version 6.2.1)

[koahnig]

@Alex_wang

For linux systems I am suggesting that you follow the rules for declaring libraries. or this here

When I read your first post, I thought you are on windows because you are using windows notation for library declaration.

AFAIK that would help in your case. For linux there has been always the split between library path (-L) and library (-l) in declaration. Not sure, if there are really any linux systems around being able to handle differently. Anyway it will not hurt following these rules. You can even do it on windows with MinGW tool chain.

@Alex_wang said in Qt5 Compile with an error "undefined reference" when linking static libraries or dynamic libraries:

main.o ... ... qt_odin.o qrc_qml.o ... ... moc_qt_odin.o
-L/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib/aarch64-linux-gnu
-L/home/suma/tx1/Linux_for_Tegra/rootfs/usr/lib
-L/home/suma/tx1/Linux_for_Tegra/rootfs/lib/aarch64-linux-gnu
/home/suma/interface/lib/tx1/libparam_msg.a <<<<<< those need a split
/home/suma/interface/lib/tx1/libengine.a <<<<<< those need a split
/home/suma/interface/open_lib/json-c-0.12.1/tx1/lib/libjson-c.a <<<<<< those need a split
-L/home/suma/tx1/qt/qt5/lib
-lQt5QuickWidgets -lQt5Quick -lQt5Widgets -lQt5Multimedia -lQt5Gui -lQt5Qml
-lQt5Network -lQt5Sql -lQt5SerialPort -lQt5Core -lGLESv2
-lpthread

I have marked in the quoted section the three lines the linker cannot understand.

@Alex_wang said in Qt5 Compile with an error "undefined reference" when linking static libraries or dynamic libraries:

LIBS += -L$$PWD/interface/lib/tx1 -llibparam_msg.a  \
             -L$$PWD/interface/lib/tx1 -llibengine.a  \
             -L$$PWD/interface/open_lib/json-c-0.12.1/tx1 -llib/libjson-c.a

This may work.
I am not sure about the notation of libraries in linux. The naming seem to be too close to windows MinGW libs.

[mvuori]

If that function is originally in a .c file, the traditional error is that in the header file (or in your manually pasted prototype) it has not been defined as extern "C".

[kshegunov]

Read this very carefully.

As @koahnig said you're not linking properly, also for static linking it's advisable (very, very advisable) you add the libraries to the PRE_TARGETDEPS variable in your project file, explanation here.

Finally, if libengine.a has dependencies of its own on dynamic libraries, those have to be linked with the application/user code, which is my "educated" guess for why od_msg_create_fix_trans can't be found (the library list is on the short side). Where is this function defined?

[Alex_wang]

@kshegunov @koahnig

Hi,
.pro has been changed :

unix:!macx: LIBS += -L$$PWD/../../../../../opt/odin/lib/tx1/ -lparam_msg
INCLUDEPATH += $$PWD/../../../../../opt/odin/lib/tx1
DEPENDPATH += $$PWD/../../../../../opt/odin/lib/tx1
unix:!macx: PRE_TARGETDEPS += $$PWD/../../../../../opt/odin/lib/tx1/libparam_msg.a

unix:!macx: LIBS += -L$$PWD/../../../../../opt/odin/lib/tx1/ -lengine
INCLUDEPATH += $$PWD/../../../../../opt/odin/lib/tx1
DEPENDPATH += $$PWD/../../../../../opt/odin/lib/tx1
unix:!macx: PRE_TARGETDEPS += $$PWD/../../../../../opt/odin/lib/tx1/libengine.a


unix:!macx: LIBS += -L$$PWD/../../../../../opt/odin/open_lib/json-c-0.12.1/tx1/lib/ -ljson-c
INCLUDEPATH += $$PWD/../../../../../opt/odin/open_lib/json-c-0.12.1/tx1/include
DEPENDPATH += $$PWD/../../../../../opt/odin/open_lib/json-c-0.12.1/tx1/include
unix:!macx: PRE_TARGETDEPS += $$PWD/../../../../../opt/odin/open_lib/json-c-0.12.1/tx1/lib/libjson-c.a

But the error still ......

[Alex_wang]

@mvuori
Hi,

I find that function is really in a .c file, and in the header file it is not be defined as extern "C".

I will try it.

[Alex_wang]

Hi,
@mvuori
@kshegunov @koahnig

Thank you for your reply

the error has been solved:
as mvuori said, the header file of the libs is not been defined extern "C"