Static members in static library

Mark81

I have a QWidget project with several sub-projects as static libraries.
One of them contains s tatic member (I tried also with a static function).


class myClass : public QObject
{
    Q_OBJECT

public:
    explicit myClass(QObject *parent = 0);
    static int myStaticMember;
}

The library compiles fine (i.e. libmyClass is generated).
In another static library of my project I want to use myStaticMember.
Thus I imported the library in the project file:

LIBS += -L$$OUT_PWD/../myClass/ -lmyClass
INCLUDEPATH += $$PWD/../myClass
DEPENDPATH += $$PWD/../myClass
PRE_TARGETDEPS += $$OUT_PWD/../myClass/libmyClass.a

Also this library compiles fine, and contains a call to that member:

#include "myClass.h"
//
qDebug() << myClass::myStaticMember;

The problem rises when I build the whole project. I get the following error:

myClass/myClass.cpp:15: error: undefined reference to `myClass::myStaticMember'

Another weird thing is that the line pointed by the error is few lines below the actual call to the myStaticMember - and it isn't related at all (I declare a QTimer...).

Why the linker cannot find the member?

kshegunov

@Mark81
What platform are you running, windows or *nix? Do you have that static member defined in the cpp file for myClass?

Mark81

@kshegunov Linux. mmm, no, it's just a public variable. What do you mean with "define in the cpp file"?

kshegunov

@Mark81 said:
Having this:

class myClass
{
     static int myStaticMember;
}

You should also do in the cpp file (usually on top):

int myClass::myStaticMember = 12345; //< Definition and initialization

On Linux the archive (static lib) is not checked for pretty much anything before linking, so you can have the *.a generated and still fail to link.

Mark81

@kshegunov Ok, I thought is was optional, not mandatory. My fault. Now it compiles fine, thanks.

kshegunov

@Mark81
No problem.