[Rd] c++ code on amd64

[Prof Brian Ripley]

You mention 'float' repeatedly.  A %f argument in Rprintf (and printf) 
refers to a _double_.  Given how little you have shown us it has to be 
entirely guesswork, but is cel.GetIntensity(1) perhaps a float?  If so 
what happens is I believe undefined and compiler-specific.  (Normally 
headers force conversions, but not for variable-argument-list functions.)

On Sun, 16 Apr 2006, Kasper Daniel Hansen wrote:

> Hi
>
> Brief synopsis:
>
> I am having a rather peculiar problem regarding a C++ library. It
> seems that functions from this library behave differently when
> compiled using R as opposed to being compiled directly from the
> command line. The problem is only seen on the amd64 platform (using
> gcc 4.0.2) and not on either of Solaris (both 32 bit and 64 bit), Mac
> OS and Windows.
>
> A bit more detail:
>
> Basically the c++ library contains a class and methods for parsing
> text files in specific formats. These files contains integers as well
> floats.
>
> If I write a stand-alone c++ program with a line like
>
>   ....
>   cout << "x: " cel.GetIndexToX(1) << " intensity: " <<
> cel.GetIntensity(1) << endl;
>   ....
>
> (here cel is pointing to a specific file while GetIndexToX returns an
> integer (in what is essentially the first row), while GetIntensity
> returns a float), it works fine: the two numbers are printed to stdout.
>
> If I instead embed the code inside R like
>
> extern "C" {
>    ....
>    Rprintf("x: %d intensity: %f", cel.GetIndexToX(1),
> cel.GetIntensity(1)):
>   ...
> }
>
> and do a R CMD INSTALL, I am able to read the integer from the file,
> but not the float. The float always returns 0.00000. This is very
> strange considering that the code is basically identical in the two
> cases (except for the extern part and inclusion of the R header
> files), and that the integer number is being read perfectly!
>
> I would say that the fact that the stand-alone program works is
> indicating that the C++ library actually works. Further indication
> that this is the case is the fact that our R package works fine on
> Mac G4, Solaris and Windows.
>
> The only real difference I can see is that the amd64 platform is the
> only little-endian 64-bit platform.
>
> My working hypothesis is that the float is being read and then
> truncated.
>
> I am extremely baffled by this. Do anyone have an idea on where I
> should start looking?
>
> System details:
>
> uname -a
> Linux shadowfax.berkeley.edu 2.6.12-1-amd64-k8-smp #1 SMP Wed Sep 28
> 02:57:49 CEST 2005 x86_64 GNU/Linux
>
> gcc --version
> gcc (GCC) 4.0.2 20050808 (prerelease) (Ubuntu 4.0.1-4ubuntu9)
>
> R is version 2.2.1 build using a standard ./configure, make step.
>
>
> /Kasper
>
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>
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595