Dear Kasper,
What do you mean with 'undefined aspect of ++'?
Every compiler has to evaluate first the expression on the right side
and then apply the result to the variable on the left side, as in:
i = i + 1;
I understand that the expression:
i = i++;
may be confusing, but the expression:
i = ++i;
should work. What about:
i = (++i); or i = {++i}
Would this also result in a warning message?
Best regards,
Christian
On 6/23/14 10:05 PM, Kasper Daniel Hansen wrote:
You're getting this message because you are using an undefined aspect of
++. Depending on compiler convention re. the interpretation of ++, your
code may be interpreted differently; ie. different compilers will
interpret the code differently. This is a bad thing.
You're presumably getting the warning now, because the compiler flag has
been added on the Bioc build servers.
There was a recent thread on this specific aspect of ++ recently, but I
forgot which email list.
Kasper
On Mon, Jun 23, 2014 at 2:54 PM, cstrato <cstr...@aon.at
<mailto:cstr...@aon.at>> wrote:
Dear Romain,
I do not know enough about compilers, but as far as I remember, they
'work' from right to left, so numsels = ++numsels should not confuse
the compiler. Anyhow I will change my code to your first suggestion
since it is more elegant.
Best regards,
Christian
On 6/23/14 7:13 PM, Romain François wrote:
Le 23 juin 2014 à 18:28, cstrato <cstr...@aon.at
<mailto:cstr...@aon.at>> a écrit :
Dear Romain,
Thank you for your suggestions, I like especially the first one.
However, you did not explain why I have never got this
warning message on any compiler, and why only one of the two
identical Ubuntu compilers did give this warning message?
Best regards,
Christian
I don’t know, but this:
numsels = ++numsels ;
seems fishy to me, and so it keeps feeling weird with the
addition of the ternary operator.
There is obviously a difference of setup between these two
machines, but I don’t have time to sherlock that for you. One of
the compilers is getting more careful than the other. Getting
warnings you did not get before is a good thing, as it helps you
update the code with that new insight.
Welcome to my world, I’m sometimes thrown all kinds of new
warnings from esoteric compilers, all of them have value .
Romain
On 6/23/14 3:45 PM, Romain François wrote:
Le 23 juin 2014 à 15:20, cstrato <cstr...@aon.at
<mailto:cstr...@aon.at>> a écrit :
Dear all,
Since many years the following C++ code does compile
on ALL Bioconductor servers (Linux, Windows, Mac)
without any warnings:
Int_t numsels = 0; //number of selected entries
...
for (Int_t i=0; i<size; i++) {
numsels = (arrMask[i] == 1) ? ++numsels :
numsels;
}//for_i
This is confusing. I would write the loop body like this:
numsels += (arrMask[i] == 1) ;
or preferably using the STL:
Int_t numsels = std::count( begin(arrMask),
end(arrMask), 1 ) ;
or some other variation of this, i.e. perhaps you don’t
have a C++11 compiler, so perhaps one of these depending
on what is arrMask:
Int_t numsels = std::count( arrMask.begin(),
arrMask.end(), 1 ) ;
Int_t numsels = std::count( arrMask, arrMask + size, 1 ) ;
Romain
Even on the recently added release server 'zin2'
Linux (Ubuntu 12.04.4 LTS) the above code compiles
w/o warnings.
However, on the new development server 'zin1' Linux
(Ubuntu 12.04.4 LTS) I get suddenly the following
warning message:
Found the following significant warnings:
XPSPreProcessing.cxx:3026:56: warning: operation
on ‘numsels’ may be undefined [-Wsequence-point]
Interestingly, both servers do not only run the same
version of Ubuntu, but also the same version of the
C++ compiler, i.e. g++ (Ubuntu/Linaro
4.6.3-1ubuntu5) 4.6.3, and use the same flags, see:
http://bioconductor.org/__checkResults/2.14/bioc-LATEST/__zin2-NodeInfo.html
<http://bioconductor.org/checkResults/2.14/bioc-LATEST/zin2-NodeInfo.html>
http://bioconductor.org/__checkResults/devel/bioc-__LATEST/zin1-NodeInfo.html
<http://bioconductor.org/checkResults/devel/bioc-LATEST/zin1-NodeInfo.html>
My question is now, why do I suddenly get the
compiler warning?
The reason why I ask at R-devel and not Bioc-devel
is that it may not only be a Bioc question, since I
found the following links:
http://c-faq.com/expr/__seqpoints.html
<http://c-faq.com/expr/seqpoints.html>
http://stackoverflow.com/__questions/16838884/why-i-got-__operation-may-be-undefined-in-__statement-expression-in-c
<http://stackoverflow.com/questions/16838884/why-i-got-operation-may-be-undefined-in-statement-expression-in-c>
I am not sure if I understand the meaning, but until
now I have never got any warning from any compiler
the I have used (including MS Visual C++).
Do I really have to replace '++numsels' with
'numsels+1'?
Best regards,
Christian
_._._._._._._._._._._._._._._.___._._
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V.i.e.n.n.a A.u.s.t.r.i.a
e.m.a.i.l: cstrato at aon.at <http://aon.at>
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