对于什么是R for Windows'“当前版本”和“安装路径”注册表项使用？

Question

Here are the two registry entries I'm asking about.**

HKEY_LOCAL_MACHINE\Software\R-core\R\Current Version
HKEY_LOCAL_MACHINE\Software\R-core\R\version\InstallPath

When R is launched from the command line (or from emacs , or statconnDCOM for that matter) it uses whatever version appears first in Windows' Path environment variable. By contrast, double clicking on a *.Rdata file uses the version pointed to by the relevant file association entry in HKEY_CLASSES_ROOT .

But when or by what are the two HKEY_LOCAL_MACHINE entries used?

EDIT: Brian Diggs points to a bundle of Windows *.bat files that do use (and modify) these registry entries, but I'm still interested in whether anything closer to 'core' R uses these. (I'm hoping the answer is 'no'.)

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** As described in the R for Windows FAQ , these entries may be set either during installation (by clicking 'Save version number in registry') or later from the command line (by typing RSetReg.exe from within $RHOME\\bin ).

Answer 1

One set of programs which use these are the R batchfiles which states

These programs set the version of R (and version of R Tools and miktex) by (1) examining environment variables (R_HOME, R_MIKTEX, R_TOOLS) or (2) if not set they look in the registry.

Answer 2

Major edit:

It looks like those registry entries are primarily there for use by external applications.

Here's why I think that.

1. grep'ing HKEY_LOCAL_MACHINE in the R sources turns up four hits in just three files. The files -- "extra.c" , "RSetReg.c" , and "rhome.c" -- are all located in R-2.15.0/src/gnuwin/ or its subdirectories.

2. The relevant occurrence appears to be that in R-2.15.0/src/gnuwin/rhome.c , where it is used by the C function get_R_HOME . That function is designed to

   /* get R_HOME from environment or registry: used in embedded apps */

   and it searches in the registry only if R_HOME if it has not yet been found in the "C environment space" or the "Windows API environment space".

3. get_R_HOME , in turn, only appears in two other files, "R-2.15.0/src/gnuwin/embeddedR.c" , and "R-2.15.0/src/gnuwin/front-ends/rtest.c" . (According to its resident readme file, the role of "R-2.15.0/src/gnuwin/front-ends/" is to make it possible to "Link[...] the R DLL into other applications".)

4. R's *NIX origins and emphasis on portability make it seem unlikely that anything close to R's core functionality would depend on registry entries. (This item's obviously way more speculative.)

Unless I hear otherwise, that's enough to convince me that the registry entries' only purpose is to provide pointers for external applications, particularly those that use an embedded instance of R.