[linrad] Re: xlinrad 02.05. Problem solved(?)

[Robert McGwier <comcast.net; rwmcgwier@xxxxxxxxxxxxxxxx>]

The first one cannot know whether or not a separate thread using a 
pointer or the variable has initialized the contents.  In the second,  
typically the construct inside the

if  (A ==0) {
}

braces, requires that A be initialized to zero and that some action 
required by the inside of braces area has been accomplished.  Otherwise, 
there would be no need for the if test.  This is typically why the 
second fails and the first does not.  If A is an unsigned integer 
quantity, it does not matter that B is unitialized.  The operation is 
legal even if the contents are not.   These kinds of assignments 
typically succeed except in the case of floating point where a floating 
point exception is thrown (if you are lucky!).

gdb and valgrind are tools that aid (as you can see) but they cannot 
tease apart all of the logical ways things can happen.  If I may,  they 
are not mind readers,  they are the assistant in the audience aiding the 
mentalist by picking the unsuspecting customer's pocket for 
information!  With that attitude,  you will find a way to properly use 
valgrind or gdb to eventually come to arrive at the error by logical 
inference and deduction.  I wish I could give a more satisfying answer 
but you can see why it is not possible for valgrind or gdb to understand 
all of the ways these things can happen.

The best case you can hope for is an explosion where valgrind gives you 
the line of interest and you back it up logically to the nexus of the 
problem.

73's
Bob





leif@xxxxxxxxxx wrote:
> Hi Bob,
>
>   
> > You will probably need to turn on the debug symbol generation and turn 
> > off optimizations and then you will be able to follow the progress.  You 
> > do not care that it is slow here,  you are attempting to find logic and 
> > other errors. 
> >     
> OK. The problem is to know all the details....
>
>   
> > gcc -g -O0  will turn off optimizations, insert debug symbols and you 
> > can then debug with gdb or valgrind. 
> >     
> Hmmm, so far gdb is black magic to me, but valgrind gives 
> info I can understand:-)
>
> I tried several times (various things) until I discovered I have to 
> put -g in the compiler stage and not the linker stage;-)
> Another thing was that I had to remove -s from the linker options....
>
> Now it works! 
>
> Is there a way to get an error message when an uninited variable
> is used ? Things like this:
> (B not initialised)
> A=B;
> .
> .
> .
> .
> if(A==0)whatever();
>
> I get an error message from the last line but not from the first one
> which may be very far away in the code an have inherited its non-init
> status through a long chain through several intermediate variables.
>
>
> 73
>
> Leif
>
>   


--
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity.  Guilty as charged!


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