QT GUI FFTSINK in C++ Flowgraph

GNU Radio
1

Hello,
I am attempting to use qt gui widgets in a C++ flowgraph. I managed to
get all of the build dependencies figured out, which was no easy task in
itself and required a lot of direct includes. Anyway, the error that I
am getting now deals directly with the make function. The line that is
giving me trouble is as follows

qtgui_sink_c_sptr qtsink = qtgui_make_sink_c (fftsize,
gr_firdes::WIN_HAMMING, 0, 1.0, “Spectrum Display”, true, true, true,
true, QWidget *parent=NULL);

Information on this function is available here.
http://gnuradio.org/redmine/projects/gnuradio/wiki/TutorialsQTGUI The
error that I am getting is that parent is undefined. I really don’t know
what to put for this. Note that I have also tried putting just NULL or
just 0 and it throws an undefined reference error (for the function
call). I was wondering if someone could give me some pointers on what to
use for parent? While I would eventually like to have both an fft and a
time domain view in a single window, I am currently just trying to get
the fft to show in its own window. Thanks ahead of time!

-Dan

2

I’ve been toying around with this a bit more. I added "#include
" to the top of my program. I also added “QWidget* parent = new
QWidget;” before my call to qtgui_make_sink_c and replaced “QWidget
*parent=NULL” white “parent”. I am now getting the following error

top_block.cc:(.text+0x8cd): undefined reference to
QWidget::QWidget(QWidget*, QFlags<Qt::WindowType>)' top_block.cc:(.text+0x94f): undefined reference toqtgui_make_sink_c(int, int, double, double, std::basic_string<char,
std::char_traits, std::allocator > const&, bool, bool,
bool, bool, QWidget*)’

I’ve double checked what little documentation I can find on
qtgui_make_sink_c and I think that I am passing appropriate parameters.
Any thoughts on what might be wrong?

-Dan

3

On Sun, Dec 16, 2012 at 5:23 PM, Daniel Labarowski
[email protected]wrote:

I’ve double checked what little documentation I can find on
qtgui_make_sink_c and I think that I am passing appropriate parameters. Any
thoughts on what might be wrong?

-Dan

This suggests that you are not linking against libgnuradio-qtgui.so.
Make
sure you are (-lgnuradio-qtgui should be used when linking).

You probably also want to use NULL for the parent. As it is now, you’re
using an empty QWidget, and I’m not sure what will happen with that, but
it
probably won’t work as expected.

From your first email, it looks like you are passing “QWiget*
parent=NULL”
as the last parameter. Just say “NULL” here, instead.

I’ve never tried to use QTGUI in C++ apps, so I’m curious to know if you
can get it to work.

Tom

4

I’ve never tried to use QTGUI in C++ apps, so I’m curious to know if
you can get it to work.

Tom

I believe that gqrx is an instance of an app that uses both QtGUI, and
Gnu Radio, and is largely written in C++, and is open source. Valuable
hints might be gleaned by looking at that source code.

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

5

On Mon, Dec 17, 2012 at 4:47 PM, Marcus D. Leech [email protected]
wrote:

I’ve never tried to use QTGUI in C++ apps, so I’m curious to know if you
can get it to work.

Tom

I believe that gqrx is an instance of an app that uses both QtGUI, and Gnu
Radio, and is largely written in C++, and is open source. Valuable
hints might be gleaned by looking at that source code.

Hi Marcus,

The initial gqrx was a python application that used gr-qtgui. Since
then I have started from scratch and created a new application using
C++ and Qt for gui but not the gr-qtgui component.

Alex

6

Thanks for the replies guys. Tom, I have modified this flowgraph
(extensively) from one of the examples and have been using its
CMakeLists.txt file (modifying it along the way of course). The commands
that I use to build it are

mkdir build
cd build
cmake …/
make

I believe that -l gnuradio-qtgui would be for g++. Since I am not using
g++ directly I tried adding the following to my CMakeLists.txt file.

libgnuradio-qtgui.so

#find_package(gnuradio-qtgui)
include_directories(/usr/local/lib)

When the find_package command did not work, I commented it out and
included the directory absolutely. I have had to do this a lot lately.
Some of the library variables seem to have not gotten set by the build
script (granted, this build is from the summer). Unfortunately I am
still getting the

undefined reference to `qtgui_make_sink_c(int, int, double, double,
std::basic_string<char, std::char_traits, std::allocator >
const&, bool, bool, bool, bool, QWidget*)’

error. My syntax is

qtgui_sink_c_sptr qtsink = qtgui_make_sink_c (fftsize,
gr_firdes::WIN_HAMMING, 0, 1.0, “Spectrum Display”, true, true, true,
true, NULL);

I am including the following relevant components

#include <qtgui_sink_c.h>
#include
#include

Can anyone spot my mistake?

-Dan

7

On Wed, Dec 19, 2012 at 2:56 AM, Daniel Labarowski
[email protected]wrote:

included the directory absolutely. I have had to do this a lot lately. Some

Can anyone spot my mistake?

-Dan

Hi Dan,

The problem is not in the includes, its in the linking library. Try
using:

target_link_libraries( )

Tom