GStreamer：在C ++中与GST_OBJECT斗争

Question

I have started to take a look into GStreamer 1.0 in the last days. The first examples worked fine but now I am at a point where I need GST_OBJECT(obj) .
When I try to compile the example using it, the compiler outputs undefined reference to symbol 'g_type_check_instance_cast' . I am using Eclipse Luna for compiling. My OS is Ubuntu 14.04, as a compiler I use GCC. In Eclipse I have added
/usr/lib/x86_64-linux-gnu/glib-2.0/include
/usr/include/gstreamer-1.0
/usr/include/glib-2.0
to the include paths of the C++ Compiler and
glib-2.0
gstnet-1.0
gstbase-1.0
gstcheck-1.0
gstreamer-1.0
gstcontroller-1.0
to the GCC C++ Linker libraries. I am new to adding external libraries to C++ so I have no idea while the compiler fails.

Short code snippet I have used:
#include <iostream>
#include <gst/gst.h>

using namespace std;

int main(int argc, char **argv) { GstElement *myFirstElement;

gst_init(&argc, &argv);

myFirstElement = gst_element_factory_make("fakesrc", "source");

if(!myFirstElement)
    return -1;

gst_object_unref(GST_OBJECT(myFirstElement));

return 0;

}`

Answer 1

Well, if I compile

#include <iostream>
#include <gst/gst.h>

using namespace std;

int main(int argc, char **argv)
{
  GstElement *myFirstElement;

  gst_init(&argc, &argv);

  myFirstElement = gst_element_factory_make("fakesrc", "source");

  if(!myFirstElement)
      return -1;

  gst_object_unref(GST_OBJECT(myFirstElement));

  return 0;
}

using

g++ -o main main.cc  `pkg-config --cflags --libs gstreamer-1.0`

everything works fine. Might be a problem with your setup...

Answer 2

Your issue might be the linking order of the libraries. When linking libraries, the order actually matter. For example, if libA requires symbol from libB, then you need to link in the order of -lA -lB. If you reverse the order then the linking would fail.

My guess is that if you linked glib before gstreamer then it would fail, as gstreamer depends on symbols from glib.