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Tcl_OpenFileChannel(3)	    Tcl Library Procedures	Tcl_OpenFileChannel(3)

______________________________________________________________________________

NAME
       Tcl_OpenFileChannel,    Tcl_OpenCommandChannel,	  Tcl_MakeFileChannel,
       Tcl_GetChannel, Tcl_RegisterChannel, Tcl_UnregisterChannel,  Tcl_Close,
       Tcl_ReadChars,	 Tcl_Read,    Tcl_GetsObj,   Tcl_Gets,	 Tcl_WriteObj,
       Tcl_WriteChars, Tcl_Write, Tcl_Flush, Tcl_Seek, Tcl_Tell,  Tcl_GetChan‐
       nelOption,  Tcl_SetChannelOption, Tcl_Eof, Tcl_InputBlocked, Tcl_Input‐
       Buffered - buffered I/O facilities using channels

SYNOPSIS
       #include <tcl.h>

       typedef ... Tcl_Channel;

       Tcl_Channel
       Tcl_OpenFileChannel(interp, fileName, mode, permissions)

       Tcl_Channel
       Tcl_OpenCommandChannel(interp, argc, argv, flags)

       Tcl_Channel							       │
       Tcl_MakeFileChannel(handle, readOrWrite)				       │

       Tcl_Channel
       Tcl_GetChannel(interp, channelName, modePtr)

       void
       Tcl_RegisterChannel(interp, channel)

       int
       Tcl_UnregisterChannel(interp, channel)

       int
       Tcl_Close(interp, channel)

       int								       │
       Tcl_ReadChars(channel, readObjPtr, charsToRead, appendFlag)	       │

       int								       │
       Tcl_Read(channel, byteBuf, bytesToRead)				       │

       int								       │
       Tcl_GetsObj(channel, lineObjPtr)					       │

       int								       │
       Tcl_Gets(channel, lineRead)					       │

       int								       │
       Tcl_WriteObj(channel, writeObjPtr)				       │

       int								       │
       Tcl_WriteChars(channel, charBuf, bytesToWrite)			       │

       int								       │
       Tcl_Write(channel, byteBuf, bytesToWrite)			       │

       int
       Tcl_Flush(channel)

       int
       Tcl_Seek(channel, offset, seekMode)

       int
       Tcl_Tell(channel)

       int
       Tcl_GetChannelOption(interp, channel, optionName, optionValue)

       int
       Tcl_SetChannelOption(interp, channel, optionName, newValue)

       int
       Tcl_Eof(channel)

       int
       Tcl_InputBlocked(channel)

       int
       Tcl_InputBuffered(channel)

ARGUMENTS
       Tcl_Interp	 *interp	    (in)      Used for error reporting
						      and to look up a channel
						      registered in it.

       char		 *fileName	    (in)      The name of a  local  or
						      network file.

       char		 *mode		    (in)      Specifies	 how  the file
						      is to be accessed.   May
						      have  any	 of the values
						      allowed  for  the	  mode
						      argument to the Tcl open
						      command.	For  Tcl_Open‐
						      CommandChannel,  may  be
						      NULL.

       int		 permissions	    (in)      POSIX-style   permission
						      flags  such as 0644.  If
						      a new file  is  created,
						      these  permissions  will
						      be set  on  the  created
						      file.

       int		 argc		    (in)      The  number  of elements
						      in argv.

       char		 **argv		    (in)      Arguments for construct‐
						      ing  a command pipeline.
						      These  values  have  the
						      same meaning as the non-
						      switch arguments to  the
						      Tcl exec command.

       int		 flags		    (in)      Specifies	 the  disposi‐
						      tion of the  stdio  han‐
						      dles  in pipeline: OR-ed
						      combination	    of
						      TCL_STDIN,   TCL_STDOUT,
						      TCL_STDERR,	   and
						      TCL_ENFORCE_MODE.	    If
						      TCL_STDIN is set,	 stdin
						      for  the	first child in
						      the  pipe	 is  the  pipe
						      channel, otherwise it is
						      the same as the standard
						      input  of	 the  invoking
						      process;	likewise   for
						      TCL_STDOUT	   and
						      TCL_STDERR.	    If
						      TCL_ENFORCE_MODE	is not
						      set, then the  pipe  can
						      redirect	stdio  handles
						      to  override  the	 stdio
						      handles	  for	 which
						      TCL_STDIN,    TCL_STDOUT
						      and TCL_STDERR have been
						      set.  If it is set, then
						      such  redirections cause
						      an error.		       │

       ClientData	 handle		    (in)			       │
						      Operating	 system	  spe‐ │
						      cific  handle for I/O to │
						      a file. For Unix this is │
						      a	 file  descriptor, for │
						      Windows it is a HANDLE.  │

       int		 readOrWrite	    (in)			       │
						      OR-ed   combination   of │
						      TCL_READABLE	   and │
						      TCL_WRITABLE to indicate │
						      what    operations   are │
						      valid on handle.	       │

       char		 *channelName	    (in)			       │
						      The name of the channel.

       int		 *modePtr	    (out)     Points  at  an   integer
						      variable	  that	  will
						      receive an OR-ed	combi‐
						      nation  of  TCL_READABLE
						      and TCL_WRITABLE	denot‐
						      ing  whether the channel
						      is open for reading  and
						      writing.

       Tcl_Channel	 channel	    (in)      A	 Tcl channel for input
						      or  output.   Must  have
						      been  the	 return	 value
						      from a procedure such as
						      Tcl_OpenFileChannel.

       Tcl_Obj		 *readObjPtr	    (in/out)			       │
						      A	  pointer   to	a  Tcl │
						      Object in which to store │
						      the characters read from │
						      the channel.	       │

       int		 charsToRead	    (in)			       │
						      The number of characters │
						      to  read	from the chan‐ │
						      nel.  If	the  channel's │
						      encoding is binary, this │
						      is  equivalent  to   the │
						      number  of bytes to read │
						      from the channel.	       │

       int		 appendFlag	    (in)			       │
						      If non-zero,  data  read │
						      from the channel will be │
						      appended to the  object. │
						      Otherwise, the data will │
						      replace	the   existing │
						      contents of the object.  │

       char		 *readBuf	    (out)			       │
						      A	 buffer	 in  which  to │
						      store  the  bytes	  read │
						      from the channel.	       │

       int		 bytesToRead	    (in)			       │
						      The  number  of bytes to │
						      read from	 the  channel. │
						      The  buffer readBuf must │
						      be large enough to  hold │
						      this many bytes.	       │

       Tcl_Obj		 *lineObjPtr	    (in/out)			       │
						      A	  pointer   to	a  Tcl │
						      object in which to store │
						      the  line	 read from the │
						      channel.	The line  read │
						      will  be appended to the │
						      current  value  of   the │
						      object.		       │

       Tcl_DString	 *lineRead	    (in/out)			       │
						      A	  pointer   to	a  Tcl │
						      dynamic string in	 which │
						      to  store	 the line read │
						      from the channel.	  Must │
						      have been initialized by │
						      the  caller.   The  line │
						      read will be appended to │
						      any data already in  the │
						      dynamic string.	       │

       Tcl_Obj		 *writeObjPtr	    (in)			       │
						      A	  pointer   to	a  Tcl │
						      Object  whose   contents │
						      will  be	output	to the │
						      channel.		       │

       CONST char	 *charBuf	    (in)			       │
						      A buffer containing  the │
						      characters  to output to │
						      the channel.	       │

       char		 *byteBuf	    (in)			       │
						      A buffer containing  the │
						      bytes  to	 output to the │
						      channel.		       │

       int		 bytesToWrite	    (in)			       │
						      The number of  bytes  to │
						      consume  from charBuf or │
						      byteBuf  and  output  to │
						      the channel.

       int		 offset		    (in)      How   far	 to  move  the
						      access  point   in   the
						      channel	at  which  the
						      next  input  or	output
						      operation	    will    be
						      applied,	 measured   in
						      bytes  from the position
						      given by seekMode.   May
						      be  either  positive  or
						      negative.

       int		 seekMode	    (in)      Relative to which	 point
						      to  seek; used with off‐
						      set to calculate the new
						      access   point  for  the
						      channel.	Legal	values
						      are  SEEK_SET, SEEK_CUR,
						      and SEEK_END.

       char		 *optionName	    (in)      The name	of  an	option
						      applicable to this chan‐
						      nel, such as  -blocking.
						      May have any of the val‐
						      ues  accepted   by   the
						      fconfigure command.

       Tcl_DString	 *optionValue	    (in)      Where to store the value
						      of an option or  a  list
						      of all options and their
						      values. Must  have  been
						      initialized by the call‐
						      er.

       char		 *newValue	    (in)      New value for the option
						      given by optionName.
_________________________________________________________________

DESCRIPTION
       The  Tcl	 channel mechanism provides a device-independent and platform-
       independent mechanism for performing buffered input and	output	opera‐
       tions  on  a  variety  of  file, socket, and device types.  The channel
       mechanism is extensible to new channel types, by providing a low	 level
       channel	driver	for  the  new  type;  the  channel driver interface is
       described in the manual entry for Tcl_CreateChannel. The channel mecha‐
       nism provides a buffering scheme modeled after Unix's standard I/O, and
       it also allows for nonblocking I/O on channels.

       The procedures described in this manual entry comprise the  C  APIs  of
       the generic layer of the channel architecture. For a description of the
       channel driver architecture and how to implement	 channel  drivers  for
       new types of channels, see the manual entry for Tcl_CreateChannel.

TCL_OPENFILECHANNEL
       Tcl_OpenFileChannel  opens  a  file specified by fileName and returns a
       channel handle that can be used to perform  input  and  output  on  the
       file.  This  API is modeled after the fopen procedure of the Unix stan‐
       dard I/O library.  The syntax and meaning of all arguments  is  similar
       to  those  given	 in  the  Tcl open command when opening a file.	 If an
       error occurs while opening  the	channel,  Tcl_OpenFileChannel  returns
       NULL  and  records  a  POSIX  error  code  that	can  be retrieved with
       Tcl_GetErrno.  In addition, if interp is non-NULL,  Tcl_OpenFileChannel
       leaves an error message in interp's result after any error.

       The  newly  created  channel  is	 not registered in the supplied inter‐
       preter; to register it, use Tcl_RegisterChannel, described  below.   If
       one  of	the  standard channels, stdin, stdout or stderr was previously
       closed, the act of creating the	new  channel  also  assigns  it	 as  a
       replacement for the standard channel.

TCL_OPENCOMMANDCHANNEL
       Tcl_OpenCommandChannel provides a C-level interface to the functions of
       the exec and open commands.  It	creates	 a  sequence  of  subprocesses
       specified by the argv and argc arguments and returns a channel that can
       be used to communicate with these  subprocesses.	  The  flags  argument
       indicates  what sort of communication will exist with the command pipe‐
       line.

       If the TCL_STDIN flag is set then the standard input for the first sub‐
       process	will  be tied to the channel: writing to the channel will pro‐
       vide input to the subprocess.  If TCL_STDIN is not set,	then  standard
       input  for  the first subprocess will be the same as this application's
       standard input.	If TCL_STDOUT is set then  standard  output  from  the
       last subprocess can be read from the channel; otherwise it goes to this
       application's standard output.  If TCL_STDERR is	 set,  standard	 error
       output  for  all subprocesses is returned to the channel and results in
       an error when the channel is closed; otherwise it goes to this applica‐
       tion's  standard	 error.	 If TCL_ENFORCE_MODE is not set, then argc and
       argv can redirect the stdio handles to override TCL_STDIN,  TCL_STDOUT,
       and  TCL_STDERR; if it is set, then it is an error for argc and argv to
       override stdio channels for which TCL_STDIN, TCL_STDOUT, and TCL_STDERR
       have been set.

       If  an  error  occurs while opening the channel, Tcl_OpenCommandChannel
       returns NULL and records a POSIX error code that can be retrieved  with
       Tcl_GetErrno.  In addition, Tcl_OpenCommandChannel leaves an error mes‐
       sage in interp->result if interp is not NULL.

       The newly created channel is not	 registered  in	 the  supplied	inter‐
       preter;	to  register it, use Tcl_RegisterChannel, described below.  If
       one of the standard channels, stdin, stdout or  stderr  was  previously
       closed,	the  act  of  creating	the  new  channel also assigns it as a
       replacement for the standard channel.

TCL_MAKEFILECHANNEL
       Tcl_MakeFileChannel makes a Tcl_Channel from an existing, platform-spe‐
       cific, file handle.  The newly created channel is not registered in the
       supplied	 interpreter;  to  register   it,   use	  Tcl_RegisterChannel,
       described  below.   If  one  of the standard channels, stdin, stdout or
       stderr was previously closed, the act of creating the new channel  also
       assigns it as a replacement for the standard channel.

TCL_GETCHANNEL
       Tcl_GetChannel  returns	a channel given the channelName used to create
       it with Tcl_CreateChannel and a pointer to a Tcl interpreter in interp.
       If  a  channel  by that name is not registered in that interpreter, the
       procedure returns NULL. If the mode argument is not NULL, it points  at
       an integer variable that will receive an OR-ed combination of TCL_READ‐
       ABLE and TCL_WRITABLE describing whether the channel is open for	 read‐
       ing and writing.

TCL_REGISTERCHANNEL
       Tcl_RegisterChannel adds a channel to the set of channels accessible in
       interp. After this call, Tcl programs executing in that interpreter can
       refer to the channel in input or output operations using the name given
       in the call to Tcl_CreateChannel.  After this call, the channel becomes
       the  property  of  the  interpreter,  and  the  caller  should not call
       Tcl_Close for the channel; the channel  will  be	 closed	 automatically
       when it is unregistered from the interpreter.

       Code  executing	outside	 of any Tcl interpreter can call Tcl_Register‐
       Channel with interp as NULL, to indicate that it wishes to hold a  ref‐
       erence  to this channel. Subsequently, the channel can be registered in
       a Tcl interpreter and it will only be closed when the  matching	number
       of  calls  to  Tcl_UnregisterChannel  have been made.  This allows code
       executing outside of any interpreter to safely hold a  reference	 to  a
       channel that is also registered in a Tcl interpreter.

TCL_UNREGISTERCHANNEL
       Tcl_UnregisterChannel removes a channel from the set of channels acces‐
       sible in interp. After this call, Tcl programs will no longer  be  able
       to  use the channel's name to refer to the channel in that interpreter.
       If this operation removed the last registration of the channel  in  any
       interpreter, the channel is also closed and destroyed.

       Code not associated with a Tcl interpreter can call Tcl_UnregisterChan‐
       nel with interp as NULL, to indicate to Tcl that it no longer  holds  a
       reference  to  that channel. If this is the last reference to the chan‐
       nel, it will now be closed.

TCL_CLOSE
       Tcl_Close destroys the channel channel, which must denote  a  currently
       open  channel.  The channel should not be registered in any interpreter
       when Tcl_Close is called. Buffered output is flushed to	the  channel's
       output  device  prior to destroying the channel, and any buffered input
       is discarded.  If this is a blocking channel, the call does not	return
       until  all  buffered  data is successfully sent to the channel's output
       device.	If this is a nonblocking channel and there is buffered	output
       that  cannot be written without blocking, the call returns immediately;
       output is flushed in the background and the channel will be closed once
       all  of	the buffered data has been output.  In this case errors during
       flushing are not reported.

       If the channel was closed successfully, Tcl_Close returns  TCL_OK.   If
       an  error occurs, Tcl_Close returns TCL_ERROR and records a POSIX error
       code that can be retrieved with Tcl_GetErrno.  If the channel is	 being
       closed  synchronously and an error occurs during closing of the channel
       and interp is not NULL, an error message is left in interp->result.

       Note: it is not safe to call Tcl_Close on a channel that has been  reg‐
       istered using Tcl_RegisterChannel; see the documentation for Tcl_Regis‐
       terChannel, above, for details. If the channel has ever been  given  as
       the  chan argument in a call to Tcl_RegisterChannel, you should instead
       use Tcl_UnregisterChannel, which will internally	 call  Tcl_Close  when
       all  calls  to  Tcl_RegisterChannel  have been matched by corresponding
       calls to Tcl_UnregisterChannel.

TCL_READCHARS AND TCL_READ						       │
       Tcl_ReadChars consumes bytes from  channel,  converting	the  bytes  to │
       UTF-8  based on the channel's encoding and storing the produced data in │
       readObjPtr's string representation.  The return value of	 Tcl_ReadChars │
       is  the	number	of  characters, up to charsToRead, that were stored in │
       objPtr.	If an error occurs while reading, the return value is  -1  and │
       Tcl_ReadChars  records  a  POSIX	 error code that can be retrieved with │
       Tcl_GetErrno.							       │

       The return value may be smaller than the value to read, indicating that │
       less  data  than requested was available.  This is called a short read. │
       In blocking mode, this can only happen on an end-of-file.  In nonblock‐ │
       ing mode, a short read can also occur if there is not enough input cur‐ │
       rently available:  Tcl_ReadChars returns	 a  short  count  rather  than │
       waiting for more data.						       │

       If the channel is in blocking mode, a return value of zero indicates an │
       end-of-file condition.  If the channel is in nonblocking mode, a return │
       value  of zero indicates either that no input is currently available or │
       an end-of-file condition.  Use Tcl_Eof  and  Tcl_InputBlocked  to  tell │
       which of these conditions actually occurred.			       │

       Tcl_ReadChars  translates  the various end-of-line representations into │
       the canonical \n internal representation according to the current  end- │
       of-line	recognition  mode.   End-of-line  recognition  and the various │
       platform-specific modes are described in the manual entry for  the  Tcl │
       fconfigure command.						       │

       As  a  performance  optimization,  when reading from a channel with the │
       encoding binary, the bytes are not converted to UTF-8 as they are read. │
       Instead,	 they  are stored in readObjPtr's internal representation as a │
       byte-array object.  The string representation of this object will  only │
       be  constructed	if  it	is needed (e.g., because of a call to Tcl_Get‐ │
       StringFromObj).	In this way, byte-oriented data can  be	 read  from  a │
       channel,	 manipulated  by  calling  Tcl_GetByteArrayFromObj and related │
       functions, and then written to a channel without the  expense  of  ever │
       converting to or from UTF-8.					       │

       Tcl_Read	 is similar to Tcl_ReadChars, except that it doesn't do encod‐ │
       ing conversions, regardless of the channel's encoding.	It  is	depre‐ │
       cated and exists for backwards compatibility with non-internationalized │
       Tcl extensions.	It consumes bytes from channel and stores them in buf, │
       performing  end-of-line	translations  on the way.  The return value of │
       Tcl_Read is the number of bytes, up to toRead,  written	in  buf.   The │
       buffer  produced	 by Tcl_Read is not NULL terminated.  Its contents are │
       valid from the zeroth position up to and excluding the  position	 indi‐ │
       cated by the return value.					       │

TCL_GETSOBJ AND TCL_GETS						       │
       Tcl_GetsObj  consumes bytes from channel, converting the bytes to UTF-8 │
       based on the channel's encoding, until a full line of  input  has  been │
       seen.   If  the	channel's  encoding is binary, each byte read from the │
       channel is treated as an individual  Unicode  character.	  All  of  the │
       characters  of  the line except for the terminating end-of-line charac‐ │
       ter(s) are appended to lineObjPtr's string representation.  The end-of- │
       line character(s) are read and discarded.			       │

       If  a  line  was successfully read, the return value is greater than or │
       equal to zero and indicates the number of bytes stored  in  lineObjPtr. │
       If  an  error  occurs, Tcl_GetsObj returns -1 and records a POSIX error │
       code that can be retrieved with Tcl_GetErrno.  Tcl_GetsObj also returns │
       -1 if the end of the file is reached; the Tcl_Eof procedure can be used │
       to distinguish an error from an end-of-file condition.		       │

       If the channel is in nonblocking mode, the return value can also be  -1 │
       if no data was available or the data that was available did not contain │
       an end-of-line character.  When -1 is  returned,	 the  Tcl_InputBlocked │
       procedure may be invoked to determine if the channel is blocked because │
       of input unavailability.						       │

       Tcl_Gets is the same as Tcl_GetsObj except the resulting characters are │
       appended	 to  the  appended to the dynamic string given by dsPtr rather │
       than a Tcl object.						       │

TCL_WRITECHARS, TCL_WRITEOBJ, AND TCL_WRITE				       │
       Tcl_WriteChars accepts bytesToWrite bytes of character data at charBuf. │
       The  UTF-8  characters  in  the	buffer	are converted to the channel's │
       encoding and queued for output to channel.  If  bytesToWrite  is	 nega‐ │
       tive,  Tcl_WriteChars expects charBuf to be NULL terminated and it out‐ │
       puts everything up to the NULL.					       │

       Data queued for output may not appear on the output device immediately, │
       due to internal buffering.  If the data should appear immediately, call │
       Tcl_Flush after the call	 to  Tcl_WriteChars,  or  set  the  -buffering │
       option  on the channel to none.	If you wish the data to appear as soon │
       as a complete line is accepted for output, set the -buffering option on │
       the channel to line mode.					       │

       The  return  value  of Tcl_WriteChars is a count of how many bytes were │
       accepted for output to the channel.  This is either greater  than  zero │
       to  indicate  success  or -1 to indicate that an error occurred.	 If an │
       error occurs, Tcl_WriteChars records a POSIX error  code	 that  may  be │
       retrieved with Tcl_GetErrno.					       │

       Newline	characters  in the output data are translated to platform-spe‐ │
       cific end-of-line sequences according to the  -translation  option  for │
       the channel.  This is done even if the channel has no encoding.	       │

       Tcl_WriteObj  is	 similar  to  Tcl_WriteChars  except  it accepts a Tcl │
       object whose contents will be output to the channel.  The UTF-8 charac‐ │
       ters  in writeObjPtr's string representation are converted to the chan‐ │
       nel's encoding and queued for output  to	 channel.   As	a  performance │
       optimization, when writing to a channel with the encoding binary, UTF-8 │
       characters are not converted as they are written.  Instead,  the	 bytes │
       in  writeObjPtr's  internal  representation  as a byte-array object are │
       written to the channel.	The byte-array representation  of  the	object │
       will  be	 constructed if it is needed.  In this way, byte-oriented data │
       can be read from a channel, manipulated by calling Tcl_GetByteArrayFro‐ │
       mObj  and  related functions, and then written to a channel without the │
       expense of ever converting to or from UTF-8.			       │

       Tcl_Write is similar to Tcl_WriteChars except that it doesn't do encod‐ │
       ing  conversions,  regardless  of the channel's encoding.  It is depre‐ │
       cated and exists for backwards compatibility with non-internationalized │
       Tcl  extensions.	  It accepts bytesToWrite bytes of data at byteBuf and │
       queues them for	output	to  channel.   If  bytesToWrite	 is  negative, │
       Tcl_Write  expects  byteBuf to be NULL terminated and it outputs every‐ │
       thing up to the NULL.

TCL_FLUSH
       Tcl_Flush causes all of the buffered output  data  for  channel	to  be
       written	to  its underlying file or device as soon as possible.	If the
       channel is in blocking mode, the call does not  return  until  all  the
       buffered data has been sent to the channel or some error occurred.  The
       call returns immediately if the channel is  nonblocking;	 it  starts  a
       background flush that will write the buffered data to the channel even‐
       tually, as fast as the channel is able to absorb it.

       The return value is normally TCL_OK.  If	 an  error  occurs,  Tcl_Flush
       returns	TCL_ERROR and records a POSIX error code that can be retrieved
       with Tcl_GetErrno.

TCL_SEEK
       Tcl_Seek moves the access point in channel where subsequent  data  will
       be  read	 or  written.  Buffered	 output	 is flushed to the channel and
       buffered input is discarded, prior to the seek operation.

       Tcl_Seek normally returns the new access point.	If  an	error  occurs,
       Tcl_Seek	 returns  -1  and  records  a  POSIX  error  code  that can be
       retrieved with Tcl_GetErrno.  After an error, the access point  may  or
       may not have been moved.

TCL_TELL
       Tcl_Tell	 returns  the current access point for a channel. The returned
       value is -1 if the channel does not support seeking.

TCL_GETCHANNELOPTION
       Tcl_GetChannelOption retrieves, in dsPtr,  the  value  of  one  of  the
       options currently in effect for a channel, or a list of all options and
       their values.  The channel argument identifies the channel for which to
       query  an  option or retrieve all options and their values.  If option‐
       Name is not NULL, it is the name of the option to query;	 the  option's
       value  is  copied  to the Tcl dynamic string denoted by optionValue. If
       optionName is NULL, the function stores an alternating list  of	option
       names  and  their  values  in  optionValue,  using a series of calls to
       Tcl_DStringAppendElement. The various  preexisting  options  and	 their
       possible	 values are described in the manual entry for the Tcl fconfig‐
       ure command. Other options can be added by each	channel	 type.	 These
       channel type specific options are described in the manual entry for the
       Tcl command that creates a channel of that type; for example, the addi‐
       tional options for TCP based channels are described in the manual entry
       for the Tcl socket command.  The procedure normally returns TCL_OK.  If
       an  error  occurs, it returns TCL_ERROR and calls Tcl_SetErrno to store
       an appropriate POSIX error code.

TCL_SETCHANNELOPTION
       Tcl_SetChannelOption sets  a  new  value	 for  an  option  on  channel.
       OptionName  is the option to set and newValue is the value to set.  The
       procedure normally returns TCL_OK.  If  an  error  occurs,  it  returns
       TCL_ERROR;   in	addition,  if interp is non-NULL, Tcl_SetChannelOption
       leaves an error message in interp->result.

TCL_EOF
       Tcl_Eof returns a nonzero value if channel encountered an end  of  file
       during the last input operation.

TCL_INPUTBLOCKED
       Tcl_InputBlocked	 returns  a nonzero value if channel is in nonblocking
       mode and the last input operation returned  less	 data  than  requested
       because there was insufficient data available.  The call always returns
       zero if the channel is in blocking mode.

TCL_INPUTBUFFERED
       Tcl_InputBuffered returns  the  number  of  bytes  of  input  currently
       buffered	 in  the internal buffers for a channel. If the channel is not
       open for reading, this function always returns zero.

PLATFORM ISSUES								       │
       The handles returned from Tcl_GetChannelHandle depend on	 the  platform │
       and  the	 channel type.	On Unix platforms, the handle is always a Unix │
       file descriptor as returned from the  open  system  call.   On  Windows │
       platforms,  the	handle	is  a file HANDLE when the channel was created │
       with Tcl_OpenFileChannel, Tcl_OpenCommandChannel, or  Tcl_MakeFileChan‐ │
       nel.  Other channel types may return a different type of handle on Win‐ │
       dows platforms.	On the Macintosh platform, the handle is a file refer‐ │
       ence number as returned from HOpenDF.

SEE ALSO
       DString(3), fconfigure(n), filename(n), fopen(2), Tcl_CreateChannel(3)

KEYWORDS
       access  point,  blocking, buffered I/O, channel, channel driver, end of
       file, flush, input, nonblocking, output, read, seek, write

Tcl				      8.1		Tcl_OpenFileChannel(3)
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