Linking Qt DLL to Qt App - unresolved references - qt

Question

I've just installed Qt 4.7.4 and trying to make a simple Qt App that uses Qt DLL. I added export/import in a class in DLL through ifdef as usual but when compiling App I het unresolved references. I also set that App depends on the DLL.
Here are the main files:
Lib.pro
QT -= gui
TARGET = Lib
TEMPLATE = lib
DEFINES += LIB_LIBRARY
SOURCES += lib.cpp
HEADERS += lib.h\
Lib_global.h
symbian {
MMP_RULES += EXPORTUNFROZEN
TARGET.UID3 = 0xE10C4E25
TARGET.CAPABILITY =
TARGET.EPOCALLOWDLLDATA = 1
addFiles.sources = Lib.dll
addFiles.path = !:/sys/bin
DEPLOYMENT += addFiles
}
unix:!symbian {
maemo5 {
target.path = /opt/usr/lib
} else {
target.path = /usr/lib
}
INSTALLS += target
}
App.pro
QT += core gui
TARGET = App
TEMPLATE = app
SOURCES += main.cpp\
mainwindow.cpp
HEADERS += mainwindow.h
FORMS += mainwindow.ui
lib.h
#ifndef LIB_H
#define LIB_H
#include "Lib_global.h"
#include <QString>
class LIBSHARED_EXPORT Lib {
public:
Lib();
~Lib();
QString Hello(QString a);
};
#endif // LIB_H
Lib_global.h
#ifndef LIB_GLOBAL_H
#define LIB_GLOBAL_H
#include <QtCore/qglobal.h>
#if defined(LIB_LIBRARY)
# define LIBSHARED_EXPORT Q_DECL_EXPORT
#else
# define LIBSHARED_EXPORT Q_DECL_IMPORT
#endif
#endif // LIB_GLOBAL_H
What's wrong with this code? Why is it unresolved reference?
In App I just include "../Lib/lib.h" and try to use the class.

Answer 1

What looks to be missing is the link between your application and your dynamic library.
I usually do something like this for my desktop (linux) apps:
INCLUDEPATH += ./include
LIBS += -L./lib -lLib
Where:
INCLUDEPATH defines the path to where your shared library .h files are located.
LIBS defines the path to where your built library is.
You can find the relevant documentation here: QMake - Declaring Other Libraries
Updated:
I was able to build the project (Linux Qt v4.7.4) and link to the library using the code you posted. I will try to clarify as my response may not be entirely clear.
The INCLUDEPATH and LIBS variables must be added to the App.pro file.
For the linker to properly find the library the paths must be adjusted to the paths you are using for your project:
LIBS += -L PATH -l LIBNAME
Supposing your folder structure is similar to the following:
Project
|_ Lib (your sharded library project files)
|_ App (your application project files)
You would adjust the variables like so:
INCLUDEPATH += ../Lib
LIBS += -L../Lib -lLib
Note that you link differently depending on your platform, you can do something like this to cover Windows and Linux:
unix {
INCLUDEPATH += ../Lib
LIBS += -L../Lib -lLib
}
win32 {
INCLUDEPATH += ../Lib
LIBS += ../Lib.lib
}