x86和ARM上的共享指针

Question

In a shared library (.so) I define a std::shared_ptr to a class object which is returned to the caller accross the library boundary to the main routine which is a Qt5.4 project. There the pointer is used in a if statement. As the bool operation is the last owner of the shared pointer it is deleted after finishing this operation and the destructor is called.

.so file (an Autotools-project):

#define STD_SHARED_PTR std::shared_ptr
#define STD_WEAK_PTR std::weak_ptr

typedef STD_SHARED_PTR<RenderingControl> RDCH;
typedef STD_WEAK_PTR<RenderingControl> WEAK;

class MediaRenderer {
    public:
        RDCH rdc();
}

class RenderingControl {
    public:
        RenderingControl();
        virtual ~RenderingControl();
}

RenderingControl::RenderingControl() {
    ...
}

RendeneringControl::~RenderingControl() {
    cerr << "Destructor called" << endl;
}

RDCH MediaRenderer::rdc() {

    RDCH rdcl = RDCH(new RenderingControl());
    long foo = rdcl.use_count();

    WEAK rdc = rdcl; 
    return rdcl;
}

.cpp (a Qt5.4 project):

typedef STD_SHARED_PTR<RenderingControl> MRDH;

MRDH renderer = MRDH(new MediaRenderer());

if (renderer->rdc()) {
    ...
    return;
}

Everything works fine on a x86 machine compiled with either Qt4.8 or Qt5.4. The destructor is called after finishing the if statement. Cross compiled for an ARM (Raspberry Pi 2) using Qt5.4, however, the destructor is not called. If I additionally add use_count() for debugging, it yields 1 in both the .so and the .cpp file on the x86, but 1 in the .so and 0 in the .cpp for the ARM.

If I compile on ARM using Qt4.8 everything is fine on ARM, too. But why does it not work on ARM using Qt5.4?

Thank you!

Answer 1

Obviously, the reason was different versions of libstdc++ I have on the same system for compiling a autotools project and a Qt project. However, even if I solved the problem by converting the library into an Qt project ensuring the use of the same libstdc++ for both parts, I do not understand why there are different versions on the same machine? Is this a specific feature of Qt? Mayby, anybody could explain...