1994-01-25  94-0036; N0423; Proposed criteria for locales and streams;
T Plum 


1. C provides a simple "go-native" call, setlocale(LC_ALL, "") .
This is important enough in non-English environments that WG14 is
sometimes asked to make this the default behavior for main.  Our
eventual C++ solution should provide some simple go-native call
(either this one or another one) such that both C and C++ libraries
are consistently imbued with the native locale.

2. C provides a "go-specific" call, setlocale(LC_xxx, str) .  Our C++
solution should provide a means (either this one or another one)
of imbuing the C and C++ locale consistently.

3.  In multi-threaded environments, the mechanism chosen should allow
(but not require) an implementation to provide the same simple
go-native and go-specific calls on a per-thread basis.

4.  The committee should hear reasons why methods are required that
are more elaborate than the mechanisms of 1, 2, and 3.

5.  Amendment 1 of ISO C ("MSE") and the X/Open "locale-object"
proposal are available for study.  Each took two or three years to
define precisely.  The committee should know how a C++ locale object
compares in semantics to these other standards, with an estimate of
the effort to standardize and implement.

The preceding items concern the question "Should we have locale
objects"; the rest assume that we decide "Yes" to this question.

6.  It should be possible to make use of one low-level locale object,
such as X/Open's, as the (hidden) implementation of the C and C++
locales.  (I believe that this is true for C.)

7.  On systems with a full C implementation of the C MSE,
it should be possible (but not required) for the C++ library to be
hosted on top of C's wide-oriented files.

8.  Programmers should be able to provide their own wide/narrow
transformations beyond what is provided by the library.

9.  The integration of C++ locale object and streams should allow
efficient implementation of inserters and extractors for char,
wchar_t, array of char, and array of wchar_t.  It should be possible
for each inserter and extractor to execute without any extra overhead
beyond byte-movement.  (The ability to add user-programmed
transformations may be useful, but should not degrade basic
operations.)

10. The POSIX locale definition is an ISO standard, so any C++ locale
object should include those POSIX features that go beyond ISO C,
including LANG, MESSAGES, time formats, etc.

11. A locale object could provide locale encapsulation for any other
object class if it provided a mode in which its construction imbued
both C and C++ locales, and its destruction restored the C and C++
locales to their entry values.