Unable to set library dependency in Qt - c++

Question

I have a project in Qt, with a class defined of the form
Project MyP --- file p.h
#ifndef P_H
#define P_H
#include <QImage>
class PP
{
public:
static QImage P1(const QImage& a);
}
#endif
Project MyP --- file p.cpp
#include "p.h"
QImage PP::P1(const QImage& a)
{
QImage b;
return b;
}
I created a test project for the class above
project test, file test.h
#ifndef TEST_H
#define TEST_H
#include <QtTest/QtTest>
class Test : public QObject
{
Q_OBJECT
private slots:
void TestSomething();
};
#endif
#include "test.h"
#include "p.h"
void Test::TestSomething()
{
QImage sourceImage = QImage("source.png");
QImage newImage = PP::P1(sourceImage);
int result = 1*2;
QVERIFY(result == 2);
}
QTEST_MAIN(Test)
doing the same thing in c++ works but there I can easily add a lib dependency)... but in Qt i get an error
error: undefined reference to `_imp___ZN6PPP1ENS_12P1MethodERK6QImage'
I tried to add library dependency like i saw here
http://qt-project.org/wiki/How_to_create_a_library_with_Qt_and_use_it_in_an_application
I added in the MyP header file
#if defined MYP_LIB
#define MYP_COMMON_DLLSPEC Q_DECL_EXPORT
#else
#define MYP_COMMON_DLLSPEC Q_DECL_IMPORT
#endif
and changed the class declaration to
class MYP_COMMON_DLLSPEC Dither
{
....
}
I added in the pro file ( I will post the entire file for ease)
TEMPLATE = lib
VERSION = 1.0.0.0
CONFIG += staticlib debug
debug {
DESTDIR = bin/debug
}
release {
DESTDIR = bin/release
}
HEADERS += \
pp.h
SOURCES += \
pp.cpp
DEFINES += MYP_LIB
then in the test project, I added in the pro file
DEPENDPATH += . ../myp
INCLUDEPATH += ../myp
win32:LIBS += ../myp/bin/debug/libmyp.a
LIBS+= -L../myp/bin/debug -lmyp
I have been unable to create a lib file, or a dll file, and have been unable to get the projects to work together. Note: they are all in the same solution.
How can I properly run the test from a separate project ?

Answer 1

You have to tell the linker to import and export (respectively) a symbol from or to a DLL, so you have to declare your class like:
Project MyP --- file p.h
#ifndef P_H
#define P_H
#if defined(MyP_LIBRARY)
# define MyPSHARED_EXPORT Q_DECL_EXPORT
#else
# define MyPSHARED_EXPORT Q_DECL_IMPORT
#endif
#include <QImage>
MyPSHARED_EXPORT class PP
{
public:
...
And add
DEFINES += MyP_LIBRARY
to your MyP.pro file
more information at
http://qt-project.org/doc/qt-4.8/sharedlibrary.html