[R-pkg-devel] Canonical way to Rprintf R_xlen_t

[Henrik Bengtsson]

"%td" is not supported on all platforms/compilers.  This is what I got
when I added it to 'matrixStats';

* using log directory 'D:/a/matrixStats/matrixStats/check/matrixStats.Rcheck'
* using R Under development (unstable) (2023-11-26 r85638 ucrt)
* using platform: x86_64-w64-mingw32
* R was compiled by
gcc.exe (GCC) 12.3.0
GNU Fortran (GCC) 12.3.0
* running under: Windows Server 2022 x64 (build 20348)
* using session charset: UTF-8
* using options '--no-manual --as-cran'
* checking for file 'matrixStats/DESCRIPTION' ... OK
* this is package 'matrixStats' version '1.1.0-9003'
* checking package namespace information ... OK
* checking package dependencies ... OK
* checking if this is a source package ... OK
* checking if there is a namespace ... OK
* checking for executable files ... OK
* checking for hidden files and directories ... OK
* checking for portable file names ... OK
* checking serialization versions ... OK
* checking whether package 'matrixStats' can be installed ... [22s] WARNING
Found the following significant warnings:
binCounts.c:25:81: warning: unknown conversion type character 't' in
format [-Wformat=]
binCounts.c:25:11: warning: too many arguments for format [-Wformat-extra-args]
binMeans.c:26:60: warning: unknown conversion type character 't' in
format [-Wformat=]
binMeans.c:26:67: warning: unknown conversion type character 't' in
format [-Wformat=]
...
See 'D:/a/matrixStats/matrixStats/check/matrixStats.Rcheck/00install.out'
for details.
* used C compiler: 'gcc.exe (GCC) 12.2.0'

It worked fine on Linux. Because of this, I resorted to the coercion
strategy, i.e. "%lld" and (long long int)value.  FWIW, on MS Windows,
I see 'ptrsize_t' being 'long long int', whereas on Linux I see 'long
int'.

/Henrik

On Tue, Nov 28, 2023 at 11:51 AM Ivan Krylov <krylov.r00t using gmail.com> wrote:
>
> On Wed, 29 Nov 2023 06:11:23 +1100
> Hugh Parsonage <hugh.parsonage using gmail.com> wrote:
>
> > Rprintf("%lld", (long long) xlength(x));
>
> This is fine. long longs are guaranteed to be at least 64 bits in size
> and are signed, just like lengths in R.
>
> > Rprintf("%td, xlength(x));
>
> Maybe if you cast it to ptrdiff_t first. Otherwise I would expect this
> to fail on an (increasingly rare) 32-bit system where R_xlen_t is int
> (which is an implementation detail).
>
> In my opinion, ptrdiff_t is just the right type for array lengths if
> they have to be signed (which is useful for Fortran interoperability),
> so Rprintf("%td", (ptrdiff_t)xlength(x)) would be my preferred option
> for now. By definition of ptrdiff_t, you can be sure [*] that there
> won't be any vectors on your system longer than PTRDIFF_MAX.
>
> > using the string macro found in Mr Kalibera's commit of r85641:
> > R_PRIdXLEN_T
>
> I think this will be the best solution once we can afford
> having our packages depend on R >= 4.4.
>
> --
> Best regards,
> Ivan
>
> [*] https://en.cppreference.com/w/c/types/ptrdiff_t posits that there
> may exist long vectors that fit in SIZE_MAX (unsigned) elements but not
> PTRDIFF_MAX (signed) elements. If such vector exists, subtracting two
> pointers to its insides may result in undefined behaviour. This may be
> already possible in a 32-bit process on Linux running with a 3G
> user-space / 1G kernel-space split. The only way around the problem is
> to use unsigned types for lengths, but that would preclude Fortran
> compatibility.
>
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