[R-pkg-devel] ucrt is not 64-bit clean

Just wanted to share something I just run into and fixed - when an R 
package is compiled for 64-bit Windows using "ucrt" C library, functions 
like ftell() and fseek() use 32-bit arguments for offsets, rather than 
64-bit.

What's worse the type "off_t" is 32-bit as well, which defeats the 
purpose of introducing off_t in the first place.

The solution for me was to replace ftell()/fseek() with MS-specific 
_lseeki64(), _ftelli64() and _fseeki64(), and redefine off_t to be 64-bit
"long long int".

So typical MS - there is a C-library to compile against but without 
changes the code only works up to 2GB.

It might be a good idea to have an R-shim to isolate ucrt() and provide 
64-bit functions for R packages.

What do you think?

best

Vladimir Dergachev