Re: default encoding on Japanese windows environment

[Ethan M. <eam...@gm...>]

On Thursday, 16 December 2021 11:50:25 PST Tatsuro MATSUOKA wrote:
> We consider the case where there is no "set encoding xxxx" in GNUPLOT.INT and GNUTERM is not specified.
> At start up, excution result of "show encoding"
> Cygwin => default (Perhaps on Linux the same)
> Windows (on Japanese env.) => sjis (ShiftJIS, old Japanese encording)
> Windows (not Japanese env.) => I do not know
> 
> Now even on Windows standard text editor notepad.exe, default encoding is utf8 but not sjis.
> Sjis encording is only for backward compatibility.

Are you sure this is set by the program and not by the system or user preferences?
 
> sjis being default encoding on windows on Japanese env. is better to be stopped.

So far as I know gnuplot would only start with encoding SJIS if the user's computer
has current locale set to use sjis.

Gnuplot's initialization is done in routine encoding_from_locale() in file encoding.c.

It first tries to use the system function
	    l = setlocale(LC_CTYPE, "");

The man page says
       If locale is an empty string, "", each part of the locale that should be  modified  is
       set according to the environment variables.  The details are implementation-dependent.
       For glibc, first (regardless of category), the  environment  variable  LC_ALL  is  in‐
       spected, next the environment variable with the same name as the category (see the ta‐
       ble above), and finally the environment variable LANG.  The first existing environment
       variable is used.  If its value is not a valid locale specification, the locale is un‐
       changed, and setlocale() returns NULL.

On linux an appropriate japanese locale string is "ja_JP.UTF-8"
but I know that Windows uses different names for locales.

Do you know if your Japanese env. machine is returning a valid locale specification at this
point?   If so, that is what gnuplot will use.   If no valid return is detected, the program
then falls through to this code:
#ifdef _WIN32
    /* get encoding from currently active codepage */
    if (encoding == S_ENC_INVALID) {
#ifndef WGP_CONSOLE
        encoding = map_codepage_to_encoding(GetACP());
#else
        encoding = map_codepage_to_encoding(GetConsoleCP());
#endif
    }
#endif

So I think that to change the initial encoding in gnuplot, the user needs to either
(1) set an appropriate environmental variable global to the session or
(2) set the code page to CP65001.

Is there a good place to find instructions on how to do this?
Should we add a section to the installation instructions or the user manual?