'''`[http://www.tcl-lang.org/man/tcl/TclCmd/chan.htm%|%chan] configure`''', a
[Tcl Commands%|%built-in] [Tcl] command, sets and retrieves configuration values for
[channel%|%channels].  It replaces the older `[fconfigure]`.


** Synopsis **

    :   '''chan configure''' ''channelId''
    :   '''chan configure''' ''channelId name''
    :   '''chan configure''' ''channelId name value'' ?''name value ...''?


** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/chan.htm%|%official reference]:   



** See Also **

   [channel]:   
   
   [open]:   
   
   [socket]:   




** Examples **

Configure a channel so that no buffering is done, meaning that all input and output are immediately 
flushed through the channel:

======
chan configure stdout -buffering none
======

Configure a channel to be byte-oriented, meaning that no newline conversions
are performed, that on input each byte is interpreted as a separate Unicocde
character, and that on output the bottom 8 bits of the number that is the code
point for each character are written to the channel:

======
chan configure $binaryDataFile -translation binary
======



** Binary **

The `binary` encoding is an alias for `iso8859-1` which is a subset of
[Unicode] comprised of the code points `\u0000`-`\u00ff` and contains the
characters in the [https://unicode.org/charts/PDF/U0000.pdf%|%Basic Latin] and
the [https://unicode.org/charts/PDF/U0080.pdf%|%Latin-1] Supplement Unicode
code charts.  `-encoding binary` was introduced as a migration aid to help with
either the transition from Tcl 7.6 to 8.0 or the transition from 8.0 to 8.1.

Warning:  `-encoding binary` turns off `-translation`, but `-encoding iso8859-1`
does not.

    :   ref [dgp] and [kbk] in [Tcl Chatroom] ,2013-12-02

When data is read from a binary channel, each byte constitutes the Unicode
character indicated by that byte.

When a string is [puts%|%put] into a binary channel, the lower 8 bits of the
number representing the code point of each character are written to the
channel.  If every character in the string has a code point of 255 or less no
data is lost.



** stdout encoding bug **

[RS] 2015-04-13: On Windows 7, stdout (if not redirected) breaks in a funny way when the encoding is changed - notice the "%" prompt:

 D:\>Tcl85\bin\tclsh
 % fconfigure stdout -encoding utf-8
 ‥
 ‥^C
 D:\>Tcl86\bin\tclsh
 % fconfigure stdout -encoding utf-8
 ‥exit

With longer output, the whole console (Cygwin bash in cmd.exe) freezes and can only be closed, but no longer be used. In cmd.exe without Cygwin, Ctrl-C makes the console responsive again.

A workaround in both cases is to pipe stdout through [cat]. When stdout is redirected to a file, the problem is likewise not seen.

This behavior was not the case in Tcl 8.4:

 D:\>Tcl84\bin\tclsh
 % fconfigure stdout -encoding utf-8
 %

[DKF]: This is a consequence of the special channel type used to handle the console on Windows (which uses direct writing to the console API using unicode characters). Its encoding should not be changed, but we can't prevent that from happening without extra magic to let channel types veto changes to generic properties (something that currently isn't supported).

Tcl 8.4 “worked” because it was doing the wrong thing entirely that just happened to be more resistant to this problem.



** Misc **

[LV] 2008 02 28:

Some of the wiki pages talk about the construct,

======
chan configure $serial_port -mode $baudRate,$plex,$bits,$polarity
======

or some such thing. The `-mode` flag, used for specifying baud rate, etc,  has
moved to [open] now. I don't know how one would change those values on an open
descriptor...

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