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[Discuss-gnuradio] Printing from c++ code

From: David Knox
Subject: [Discuss-gnuradio] Printing from c++ code
Date: Wed, 14 Oct 2009 07:03:59 -0700 (PDT)

I am unable to print from C++ code in gnuradio.  I have tried various
combinations of included libraries and different types of print statements
in my C++ code.  However, nothing that I have tried yet (see some attempts
below) has let me see any output from the command terminal (where my printed
python output appears).  I found an old response from Eric B. for a similar
problem, but the offered solution did not work for me either.

// #include <iostream>   // DAK
#include <cstdio>
// #include <stdio.h>   // DAK
// #include <iostream> // DAK
#include <cstring>
 fprintf(stdout, "\nTEST"); 
 fprintf(stderr, "\nTEST");  
 printf ("\nThis is a test"); 
 fprintf(stderr, "Samples Processed: %d\n", d_processed), fflush(stderr);

During the make/make install process (executed from the /src and /src/lib
directories after my experimental changes; not sure where I'm supposed to do
this).  I see errors if my C++ syntax is not correct, so presumably my
changes are actually being compiled and I also see the corresponding object
file times changing appropriately.  There could well be a problem with the
importing of modules in python or C++ and/or my directory structure or
paths.... sort of why I need the print statements to work in the first

I don't claim to understand the hierarchy of python/swig/c++ calls or the
autotools processes yet.  My basic task is to figure out the execution
progress and sequencing of some routines written by others (which are a bit
more complicated than the one in D. Shen's tutorial).  I want to understand
the control flow for some ucla 802.15.4 extension code to gnuradio,
specifically in the receive direction.  

In general, how should/could standard I/O work out of a C++ program through
SWIG into python?  Could someone tell me what is *supposed* to work (i.e.
maybe the pertinent #include and (f)printf statements.  Alternatively, maybe
someone could give alternatives to my primitive approach for understanding
python/C++ program control flow and calling structure?  I have tried using
the python interpreter and manually listing modules and module paths after
each encountered import statement; pretty tedious.

Presumably, there could be issues if C++ print statements get executed at
the same rate as RF data is processed... but right now being swamped by
print statement output from the signal processing code would be a welcome

Thanks, David

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