Compatibility of external C code across platforms

A package I have written makes considerable use of external C code. 
There appear to be no problems building a Windows binary with the 
GNU C compiler, but now I would like to make the package available 
for other platforms.  A stringent check of the code with the gcc 
options '-Wall -pedantic' flags many nested functions and 
variable-length arrays that are not allowed in ISO C.  Is it 
essential that distributed C source code for R packages conforms to 
ISO C in this respect?  I'm working in Windows XP with R2.9.2 and 
Rtools 2.9.
Yes, it is essential.  R does not assume gcc, and it does not even 
assume gcc 4.x (and people are still using gcc 3.x on some platforms, 
e.g. the sunfreeware R builds).  This is why we publish test result on 
CRAN for a completely different compiler (from SunPro).

However, if is not clear which standard you mean by 'ISO C': assuming 
C99 is fairly safe, but GNU extensions from C99 are not -- nested 
functions are one such.
[Incidentally, when I use a makevars.win file to include these gcc 
options in Rcmd build etc. the problem with variable-length arrays 
is not flagged; maybe my command-line gcc is a different version 
from that in Rtools]
Well, you (and only you) can easily check that for yourself, but the 
other flags also matter, especially --std.  Because it has been needed 
for the use of the MinGW headers, R on Windows is built with 
--std=gnu99.  (Linux headers have a similar problem: using --std=c99 
disables some features we test for in configure and wish to use -- and 
there are OS features, not language extensions.)
Murray Efford
University of Otago
Dunedin, New Zealand
murray.efford at otago.ac.nz<mailto:murray.efford at otago.ac.nz>

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Brian D. Ripley,                  ripley at stats.ox.ac.uk
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Compatibility of external C code across platforms

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