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

Abrar

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.

SGaist

Hi,

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

Abrar

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/

SGaist

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.

Abrar

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

SGaist

You already know:

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

LIBS += -L/usr/lib

That's the correct way.

Abrar

Is there any other way without specifying the lib path?

SGaist

What's the problem with that ?

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

Abrar

Thanks for the alternative...

saber

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

Abrar

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

saber

@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.

Abrar

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

JonB

@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?

Abrar

@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....

SGaist

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 ?

Abrar

@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?

SGaist

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.

Abrar

#-------------------------------------------------
#
# 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

SGaist

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