From cstrato at aon.at  Mon Jun 23 15:20:12 2014
From: cstrato at aon.at (cstrato)
Date: Mon, 23 Jun 2014 15:20:12 +0200
Subject: [Rd] =?windows-1252?q?operation_on_=91numsels=92_may_be_undefined?=
Message-ID: <53A8298C.9010605@aon.at>

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

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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[Rd] =?windows-1252?q?operation_on_=91numsels=92_may_be_undefined?=
cstrato