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encoding(n) Tcl Built-In Commands encoding(n)
encoding - Manipulate encodings
encoding option ?arg arg ...?
Strings in Tcl are logically a sequence of 16-bit Unicode characters.
These strings are represented in memory as a sequence of bytes that may
be in one of several encodings: modified UTF-8 (which uses 1 to 3 bytes
per character), 16-bit "Unicode" (which uses 2 bytes per character,
with an endianness that is dependent on the host architecture), and
binary (which uses a single byte per character but only handles a
restricted range of characters). Tcl does not guarantee to always use
the same encoding for the same string.
Different operating system interfaces or applications may generate
strings in other encodings such as Shift-JIS. The encoding command
helps to bridge the gap between Unicode and these other formats.
Performs one of several encoding related operations, depending on
option. The legal options are:
encoding convertfrom ?encoding? data
Convert data to Unicode from the specified encoding. The
characters in data are treated as binary data where the lower
8-bits of each character is taken as a single byte. The
resulting sequence of bytes is treated as a string in the
specified encoding. If encoding is not specified, the current
system encoding is used.
encoding convertto ?encoding? string
Convert string from Unicode to the specified encoding. The
result is a sequence of bytes that represents the converted
string. Each byte is stored in the lower 8-bits of a Unicode
character (indeed, the resulting string is a binary string as
far as Tcl is concerned, at least initially). If encoding is
not specified, the current system encoding is used.
encoding dirs ?directoryList?
Tcl can load encoding data files from the file system that
describe additional encodings for it to work with. This command
sets the search path for *.enc encoding data files to the list
of directories directoryList. If directoryList is omitted then
the command returns the current list of directories that make up
the search path. It is an error for directoryList to not be a
valid list. If, when a search for an encoding data file is
happening, an element in directoryList does not refer to a
readable, searchable directory, that element is ignored.
Returns a list containing the names of all of the encodings that
are currently available. The encodings "utf-8" and "iso8859-1"
are guaranteed to be present in the list.
encoding system ?encoding?
Set the system encoding to encoding. If encoding is omitted then
the command returns the current system encoding. The system
encoding is used whenever Tcl passes strings to system calls.
It is common practice to write script files using a text editor that
produces output in the euc-jp encoding, which represents the ASCII
characters as singe bytes and Japanese characters as two bytes. This
makes it easy to embed literal strings that correspond to non-ASCII
characters by simply typing the strings in place in the script.
However, because the source command always reads files using the
current system encoding, Tcl will only source such files correctly when
the encoding used to write the file is the same. This tends not to be
true in an internationalized setting. For example, if such a file was
sourced in North America (where the ISO8859-1 is normally used), each
byte in the file would be treated as a separate character that maps to
the 00 page in Unicode. The resulting Tcl strings will not contain the
expected Japanese characters. Instead, they will contain a sequence of
Latin-1 characters that correspond to the bytes of the original string.
The encoding command can be used to convert this string to the expected
Japanese Unicode characters. For example,
set s [encoding convertfrom euc-jp "\xA4\xCF"]
would return the Unicode string "\u306F", which is the Hiragana letter
Tcl 8.1 encoding(n)