@node Internationalisation
@chapter Internationalisation

Internationalisation in pspp is complicated.
The most annoying aspect is that of character-encoding.
This chapter attempts to describe the problems and current ways 
in which they are addressed.


@section The working locales
Pspp has three ``working'' locales:

@itemize
@item The locale of the user interface.
@item The locale of the output.
@item The locale of the data. Only the character encoding is relevant.
@end itemize

Each of these locales may, at different times take 
separate (or identical) values.
So for example, a French statistician can use pspp to prepare a report 
in the English language, using 
a datafile which has been created by a Japanese researcher hence 
uses a Japanese character set.

It's rarely, if ever, necessary to interrogate the system to find out
the values of the 3 locales.
However it's important to be aware of the source (destination) locale
when reading (writing) string data.
When transfering data between a source and a destination, the appropriate
recoding must be performed.


@subsection The user interface locale
This is the locale which is visible to the person using pspp.
Error messages and confidence indications  are written in this locale.
For example ``Cannot open file'' will be written in the user interface locale.

This locale is set from the environment of the user who starts pspp@{ire@} or
from the system locale if not set.

@subsection The output locale
This locale is the one that should be visible to the person reading a 
report generated by pspp.  Non-data related strings (Eg: ``Page number'',
``Standard Deviation'' etc.) will appear in this locale.

@subsection The data locale
This locale is the one associated with the data being analysed with pspp.
The only important aspect of this locale is the character encoding.
@footnote {It might also be desirable for the LC_COLLATE category to be used for the purposes of sorting data.}
The dictionary pertaining to the data contains a field denoting the encoding.
Any string data stored in a @union{value} will be encoded in the
dictionary's character set.


@section System files
@file{*.sav} files contain a field which is supposed to identify the encoding
of the data they contain (@pxref{Machine Integer Info Record}).  
However, many
files produced by early versions of spss set this to ``2'' (ASCII) regardless
of the encoding of the data.
Later versions contain an additional
record (@pxref{Character Encoding Record}) describing the encoding.
When a system file is read, the dictionary's encoding is set using information 
gleened from the system file.
If the encoding cannot be determined or would be unreliable, then it 
remains unset.


@section GUI
The psppire graphic user interface is written using the Gtk+ api, for which 
all strings must be encoded in UTF8.
All strings passed to the GTK+/GLib library functions (except for filenames)
must be UTF-8 encoded otherwise errors will occur.
Thus, for the purposes of the programming psppire, the user interface locale 
should be assumed to be UTF8, even if setlocale and/or nl_langinfo
indicates otherwise.

@subsection Filenames
The GLib API has some special functions for dealing with filenames.
Strings returned from functions like gtk_file_chooser_dialog_get_name are not, 
in general, encoded in UTF8, but in ``filename'' encoding.
If that filename is passed to another GLib function which expects a filename, 
no conversion is necessary.
If it's passed to a function for the purposes of displaying it (eg. in a 
window's title-bar) it must be converted to UTF8 --- there is a special 
function for this: g_filename_display_name or g_filename_basename.
If however, a filename needs to be passed outside of GTK+/GLib (for example to fopen) it must be converted to the local system encoding.


@section Existing locale handling functions
The major aspect of locale handling which the programmer has to consider is
that of character encoding.

The following function is used to recode strings:

@deftypefun char * recode_string (const char *@var{to}, const char *@var{from}, const char *@var{text}, int @var{len});

Converts the string @var{text}, which is encoded in @var{from} to a new string encoded in @var{to} encoding.
If @var{len} is not -1, then it must be the number of bytes in @var{text}.
It is the caller's responsibility to free the returned string when no 
longer required.
@end deftypefun

In order to minimise the number of conversions required, and to simplify 
design, PSPP attempts to store all internal strings in UTF8 encoding.
Thus, when reading system and portable files (or any other data source),
the following items are immediately converted to UTF8 encoding:
@itemize
@item Variable names
@item Variable labels
@item Value labels
@end itemize
Conversely, when writing system files, these are converted back to the
encoding of that system file.

String data stored in union values are left in their original encoding.
These will be converted by the data_in/data_out functions.



@section Quirks
For historical reasons, not all locale handling follows posix conventions.
This makes it difficult (impossible?) to elegantly handle the issues.
For example, it would make sense for the gui's datasheet to display
numbers formatted according to the LC_NUMERIC category of the data locale.
Instead however there is the @func{data_out} function 
(@pxref{Obtaining Properties of Format Types}) which uses the
@func{settings_get_decimal_char} function instead of the decimal separator 
of the locale.  Similarly, formatting of monetary values is displayed 
in a pspp/spss specific fashion instead of using the LC_MONETARY category.



@c  LocalWords:  pspp itemize Eg LC Spss cmd sav pxref spss GUI psppire Gtk api
@c  LocalWords:  UTF gtk setlocale nl langinfo deftypefun enum conv var const
@c  LocalWords:  int len gui struct val utf GtkWidget posix gui's datasheet
@c  LocalWords:  func
