Qt Creator does not find functions inside library

Question

I'm on Ubuntu 13.04 trying to use functions from the gsettingsschema.h library

This is my .pro file

QT+=core
QT-=gui
TARGET=gsettings_test
CONFIG+=console
CONFIG-=app_bundle

CONFIG+=link_pkgconfig
PKGCONFIG+=gio-2.0

TEMPLATE=app

SOURCES+=main.cpp

pkg-config --libs gio-2.0 reports :

-lgio-2.0 -lgobject-2.0 -lglib-2.0

which sounds good to me.

In my program I use both the gio/gio.h and gio/gsettingsschema.h libraries. The compiler is able to find the functions from gio.h (like g_settings_new_full()) but it is not able to find the functions from gsettingsschema.h

I get an error like:

undefined reference to 'g_settings_schema_source_get_default()'

What's happening here?

EDIT: Full compilation output (as reported from Qt Creator):

01:46:09: Running steps for project gsettings_test...
01:46:09: Starting: "/usr/bin/qmake" /home/alex/Qt/gsettings_test/gsettings_test.pro -r -spec linux-g++ CONFIG+=debug CONFIG+=declarative_debug CONFIG+=qml_debug
01:46:09: The process "/usr/bin/qmake" exited normally.
01:46:09: Starting: "/usr/bin/make" 
g++  -o gsettings_test main.o   -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lQt5Core -lpthread 
main.o: In function `gsettings_get(QString, QString)':
/home/alex/Qt/build-gsettings_test-Desktop-Debug/../gsettings_test/main.cpp:17: undefined reference to `g_settings_schema_source_get_default()'
/home/alex/Qt/build-gsettings_test-Desktop-Debug/../gsettings_test/main.cpp:17: undefined reference to `g_settings_schema_source_ref(_GSettingsSchemaSource*)'
/home/alex/Qt/build-gsettings_test-Desktop-Debug/../gsettings_test/main.cpp:19: undefined reference to `g_settings_schema_source_lookup(_GSettingsSchemaSource*, char const*, int)'
collect2: error: ld returned 1 exit status
make: *** [gsettings_test] Error 1
01:46:10: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project gsettings_test (kit: Desktop)
When executing step 'Make'
01:46:10: Elapsed time: 00:01.

Libgio exact filename:

/usr/lib/i386-linux-gnu/libgio-2.0.so.0.3600.0

Helpful command:

alex@MaD-pc:~$ sudo ldconfig -v | grep gio
[sudo] password for alex: 
/sbin/ldconfig.real: Can't stat /lib/i686-linux-gnu: No such file or directory
/sbin/ldconfig.real: Can't stat /usr/lib/i686-linux-gnu: No such file or directory
/sbin/ldconfig.real: Path `/lib/i386-linux-gnu' given more than once
/sbin/ldconfig.real: Path `/usr/lib/i386-linux-gnu' given more than once
    libgiomm-2.4.so.1 -> libgiomm-2.4.so.1.3.0
    libgio-2.0.so.0 -> libgio-2.0.so.0.3600.0

Answer 1

I know this is rather outdated, but I recently had the same issue, found this question without any real answer and was finally able to solve it. So hopefully this will help others having the same issue.

The problem was related to different function name mangling between C and C++, so if you include the GLib files from C++ code, you will get the undefined reference errors.

The solution was to change my includes from

#include <gio/gio.h>
#include <glib.h>

to

extern "C" {
#include <gio/gio.h>
#include <glib.h>
}

After that, compilation (and linking!) worked just fine.