Hi Christian,
On 06/23/2014 11:54 AM, cstrato wrote:
Dear Romain,
I do not know enough about compilers, but as far as I remember, they
'work' from right to left,
Not necessarily. So you should not rely on that. This is what the
(somewhat obscure) warning you see on zin1 is trying to tell you.
Personally I would just do:
if (arrMask[i] == 1) numsels++;
which is the standard way to implement the "if (some condition)
then increment counter" idiom.
As Kasper mentioned, a similar issue was recently discussed here:
https://stat.ethz.ch/pipermail/bioc-devel/2014-June/005858.html
Cheers,
H.
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> 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> 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/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://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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