4. Why Qt can't detect library from /usr/lib...

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Why Qt can't detect library from /usr/lib...


  • I created a library of my own and i install it using

    sudo make install

    And my library file successfully builds and copies at "/usr/lib". But when I include the library to another app of mine by

    LIBS += -llibraryname

    When building it says 'undefined reference to libraryFunction'. But if I do this

    LIBS += -L/usr/lib -llibraryname

    It got no error.
    Please tell me why is this happens.

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  • Lifetime Qt Champion

    Hi,

    Run gcc -print-search-dirs, what do you get ?

    1

  • I found this...

    install: /usr/lib/gcc/x86_64-linux-gnu/7/
programs: =/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/bin/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/bin/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/bin/
libraries: =/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/lib/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/lib/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../lib/:/lib/x86_64-linux-gnu/7/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/7/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/lib/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../:/lib/:/usr/lib/
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  • Lifetime Qt Champion

    So as you can see, /usr/lib/ is not in the search path list, hence you have to add it yourself to your projects. Nothing Qt specific here.

    1

  • Can you please tell me how to do so...

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  • Lifetime Qt Champion

    You already know:

    @Abrar said in Why Qt can't detect library from /usr/lib...:

    LIBS += -L/usr/lib

    That's the correct way.

    1

  • Is there any other way without specifying the lib path?

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  • Lifetime Qt Champion

    What's the problem with that ?

    An alternative for you is to set the LIBRARY_PATH environment variable.

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  • Thanks for the alternative...

    0 1 Reply

  • @Abrar i think this way calling lib is standard as it is included in qt.

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  • Can you tell me what is the standard way @saber ....

    0 1 Reply

  • @Abrar both

    LIBS += -llibraryname

    and

    LIBS += -L/usr/lib -llibraryname

    i am pretty sure , i know only this tow way. i think @mrjj , @JonB , @VRonin can help you better.

    0 2 Replies

  • @saber Ok i am waiting for there statement...
    @mrjj , @JonB , @VRonin

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  • @saber
    Like @SGaist has said, you change the library search path you must either use -L... or alter the LIBRARY_PATH environment variable. What is the problem with one of these?

    0 1 Reply

  • @JonB Actually there is no problem. But I just faced another issue that is I created another library and when I include that by -llibraryname that just builds fine...
    And why is that. As one(my 2nd library) got the path but other(1st library) can't....
    !!!
    Please reply....

    0
  • Lifetime Qt Champion

    Where's that library located ?
    How are you linking to it ?
    Do you have any flags set for it that is not set for the first one ?

    0 1 Reply

  • @SGaist the 2nd library also installs at /usr/lib
    And I just link it by typing
    LIBS += -llibraryname
    Like the 1st library.
    But didn't add any more thing. And also I test two of them at once.
    Is there any thing you can tell what is happening?

    0
  • Lifetime Qt Champion

    As already asked, show your .pro file.

    From what you wrote, you just added a new library to the list. So the folder was already added earlier.

    1 

  • #-------------------------------------------------
#
# Project created by QtCreator 2018-08-20T09:12:54
#
#-------------------------------------------------

QT       += core gui widgets

TARGET = help
TEMPLATE = app

# library for theme
unix:!macx: LIBS += -lcprime
unix:!macx: LIBS += -lcsys

SOURCES += \
    main.cpp \
    help.cpp

HEADERS += \
    help.h

FORMS += \
    help.ui

RESOURCES += \
    icons.qrc

# Disable warnings, enable threading support and c++11 
CONFIG += thread silent build_all c++11

# Disable Debug on Release
# CONFIG(release):DEFINES += QT_NO_DEBUG_OUTPUT

# Build location

BUILD_PREFIX = $$(CA_BUILD_DIR)

isEmpty( BUILD_PREFIX ) {
        BUILD_PREFIX = ./build
}

MOC_DIR       = $$BUILD_PREFIX/moc-qt5
OBJECTS_DIR   = $$BUILD_PREFIX/obj-qt5
RCC_DIR	      = $$BUILD_PREFIX/qrc-qt5
UI_DIR        = $$BUILD_PREFIX/uic-qt5


unix {
        isEmpty(PREFIX) {
                PREFIX = /usr
        }
        BINDIR = $$PREFIX/bin

        target.path = $$BINDIR

        desktop.path = $$PREFIX/share/applications/
        desktop.files = "Help CoreApps.desktop"

        icons.path = $$PREFIX/share/coreapps/icons/
        icons.files = icons/Help.svg

        INSTALLS += target icons desktop
}

DEFINES += QT_DEPRECATED_WARNINGS
DEFINES += "HAVE_POSIX_OPENPT"

    This is the .pro file of my application.
    And my 1st library

    QT       += widgets core network gui charts concurrent dbus

TARGET = csys
TEMPLATE = lib

# disable all build warnings
CONFIG += silent warn_on static

# Disable Debug on Release
#CONFIG(release):DEFINES += QT_NO_DEBUG_OUTPUT

VERSION = 1.0.10
DEFINES += LIBCSYS_LIBRARY

HEADERS += \
    csys/cpu_info.h \
    csys/disk_info.h \
    csys/memory_info.h \
    csys/network_info.h \
    csys/process.h \
    csys/process_info.h \
    csys/system_info.h \
    csys/command_util.h \
    csys/file_util.h \
    csys/format_util.h \
    csys/battery.h \
    csys/info_manager.h \
    csys/upower.h \
    csys/udisks2.h \
    libcsys_global.h

SOURCES += \
    csys/cpu_info.cpp \
    csys/disk_info.cpp \
    csys/memory_info.cpp \
    csys/network_info.cpp \
    csys/process.cpp \
    csys/process_info.cpp \
    csys/system_info.cpp \
    csys/command_util.cpp \
    csys/file_util.cpp \
    csys/format_util.cpp \
    csys/battery.cpp \
    csys/info_manager.cpp \
    csys/upower.cpp \
    csys/udisks2.cpp

MOC_DIR			= ../build/moc
OBJECTS_DIR		= ../build/obj
RCC_DIR			= ../build/qrc
UI_DIR			= ../build/uic

unix {
        isEmpty(PREFIX) {
                PREFIX = /usr
        }

        INSTALLS	+= target includes
        CONFIG		+= create_pc no_install_prl link_pkgconfig
        contains(DEFINES, LIB64): target.path = $$INSTALL_PREFIX/lib64
        else: target.path = $$INSTALL_PREFIX/lib

        target.path			= $$PREFIX/lib/
        includes.files	                = libcsys_global.h csys/*.h
        includes.path		        = $$PREFIX/include/csys

        QMAKE_PKGCONFIG_NAME = libcsys
        QMAKE_PKGCONFIG_DESCRIPTION = Library for coreapps
        QMAKE_PKGCONFIG_PREFIX  = $$INSTALL_PREFIX
        QMAKE_PKGCONFIG_LIBDIR  = $$target.path
        QMAKE_PKGCONFIG_INCDIR  = $$includes.path
        QMAKE_PKGCONFIG_VERSION = $$VERSION
        QMAKE_PKGCONFIG_DESTDIR = pkgconfig
}

    And 2nd Library is

    QT       += widgets core gui

TARGET    = cprime
TEMPLATE  = lib

# disable all build warnings
CONFIG   += silent warn_on thread silent build_all c++11

DEFINES  += LIBCPRIME_LIBRARY

INCLUDEPATH += ./cprime/
DEPENDPATH  += ./cprime/

# Disable Debug on Release
#CONFIG(release):DEFINES += QT_NO_DEBUG_OUTPUT

VERSION  = 1.1.1
DEFINES += LIBCPRIME_LIBRARY

MOC_DIR			= ../build/moc
OBJECTS_DIR		= ../build/obj
RCC_DIR			= ../build/qrc
UI_DIR			= ../build/uic

unix {
        isEmpty(PREFIX) {
                PREFIX = /usr
        }

        INSTALLS	 += target includes data themefiles
        CONFIG		 += create_pc no_install_prl link_pkgconfig
        contains(DEFINES, LIB64): target.path = $$INSTALL_PREFIX/lib64
        else: target.path = $$INSTALL_PREFIX/lib

        target.path	  = $$PREFIX/lib/

        includes.files    = cprime/*.h libcprime_global.h
        includes.path     = $$PREFIX/include/cprime/

        data.path         = $$PREFIX/share/coreapps/docs
        data.files        = docs/Changelog docs/LICENSE docs/To-Do.txt

        themefiles.path   = $$PREFIX/share/coreapps/Theme
        themefiles.files  = style/*.qss style/*.ini

        QMAKE_PKGCONFIG_NAME        = libcprime
        QMAKE_PKGCONFIG_DESCRIPTION = Library for coreapps
        QMAKE_PKGCONFIG_PREFIX      = $$INSTALL_PREFIX
        QMAKE_PKGCONFIG_LIBDIR      = $$target.path
        QMAKE_PKGCONFIG_INCDIR      = $$includes.path
        QMAKE_PKGCONFIG_VERSION     = $$VERSION
        QMAKE_PKGCONFIG_DESTDIR     = pkgconfig
}

HEADERS += \
    cprime/globalfunctions.h \
    cprime/utilities.h \
    cprime/settingsmanage.h \
    cprime/bookmarkmanage.h \
    cprime/bookmarkdialog.h \
    libcprime_global.h \

SOURCES += \
    cprime/globalfunctions.cpp \
    cprime/utilities.cpp \
    cprime/settingsmanage.cpp \
    cprime/bookmarkmanage.cpp \
    cprime/bookmarkdialog.cpp
    
FORMS += \
    cprime/bookmarkdialog.ui
    0 1 Reply
  • Lifetime Qt Champion

    Did you check whether you have these libraires in multiple places on your system ?

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  • @Abrar i think you should check if it is installed earlier in other places by you while you are testing.

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  • That's not installed anywhere else. But the thing is, i found this problem on xubuntu 18.04 at Qt 5.9. But i tried this on Ubuntu 18.04 at Qt 5.9 and it works without typing
    -L/usr/lib
    i think i have to use -L/usr/lib for me...
    And i found my solution. Like
    LIBS += -L/usr/lib -llibraryname
    Thanks all of you...

    0
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