Why has assignment to a gr_complex variable (GNU Radio) stopped working for me?

Question

In the block definition for my custom SDR transceiver hardware I use the following complex variable:

gr_complex complexSample;

In my code, which has worked successfully for two years before a recent upgrade to the latest gnuradio release, I use the following assignments:

complexSample.real() = realInt;
complexSample.imag()= imagInt;

However, when I try to compile now, I get the following error:

error: lvalue required as left operand of assignment

Frustratingly, if I remove the pair of parentheses, I get the following error:

error: invalid use of member function 'void std::complex::imag(float)' (did you forget the '()'? )

The original version of gnuradio I have been using is 3.7.5-5, and the latest I have upgraded to is: 3.7.10.1-2.

Has something significant changed between these two releases which could explain this difference in behaviour?

If so, what is the solution?

Could this be something to do with 'Volk integration' (whatever that is...).

score 3 · Answer 1 · answered May 01 '18 at 07:33

3

No, GNU Radio didn't change gr_complex. It's still but an alias for std::complex<float>.

What probably has changed is that you're now using a compiler set to C++14, and that makes std::complex<float>.real() return a const that you can't assign to. (I think that's what happens.)

You should either just construct the value like you mean to, i.e.

gr_complex foo(realpart, imagpart)

or use the setters

gr_complex foo;
foo.real(realpart);
foo.imag(imagpart);

answered May 01 '18 at 07:33

Marcus Müller

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Thank you, also, and for the useful explanation. – Caleb Price May 01 '18 at 22:18
Thanks Marcus, could you also tell me how to define an 'exp(j(2*pifT+phase))' type of expression in gnuradio using c++ ? – Dec 18 '19 at 08:55
sounds like a job for the "rotator" block. Or, look at that block's source code. – Marcus Müller Dec 18 '19 at 12:21

score 2 · Answer 2 · answered May 01 '18 at 07:25

2

As the error message shows, gr_complex is a typedef for std::complex<float>. That means the .real() and .imag() methods are getters, not setters.

That's not what you want anyway. You just want to assign the number, not its separate components: complexSample = gr_complex{realInt, imagInt}.

answered May 01 '18 at 07:25

MSalters

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Thanks Salters, could you also tell me how to define an 'exp(j(2*pifT+phase))' type of expression in gnuradio using c++ ? – Dec 18 '19 at 08:55

Why has assignment to a gr_complex variable (GNU Radio) stopped working for me?

2 Answers2