'\" '\" Copyright (c) 1996-1997 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) $Id: OpenFileChnl.3,v 1.2 2001/09/14 01:42:13 zlaski Exp $ .so man.macros .TH Tcl_OpenFileChannel 3 8.0 Tcl "Tcl Library Procedures" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME Tcl_OpenFileChannel, Tcl_OpenCommandChannel, Tcl_MakeFileChannel, Tcl_GetChannel, Tcl_RegisterChannel, Tcl_UnregisterChannel, Tcl_Close, Tcl_Read, Tcl_Gets, Tcl_Write, Tcl_Flush, Tcl_Seek, Tcl_Tell, Tcl_Eof, Tcl_InputBlocked, Tcl_InputBuffered, Tcl_GetChannelOption, Tcl_SetChannelOption \- buffered I/O facilities using channels .SH SYNOPSIS .nf \fB#include <tcl.h>\fR .sp typedef ... Tcl_Channel; .sp Tcl_Channel \fBTcl_OpenFileChannel\fR(\fIinterp, fileName, mode, permissions\fR) .sp Tcl_Channel \fBTcl_OpenCommandChannel\fR(\fIinterp, argc, argv, flags\fR) .VS .sp Tcl_Channel \fBTcl_MakeFileChannel\fR(\fIhandle, readOrWrite\fR) .VE .sp Tcl_Channel \fBTcl_GetChannel\fR(\fIinterp, channelName, modePtr\fR) .sp void \fBTcl_RegisterChannel\fR(\fIinterp, channel\fR) .sp int \fBTcl_UnregisterChannel\fR(\fIinterp, channel\fR) .sp int \fBTcl_Close\fR(\fIinterp, channel\fR) .sp int \fBTcl_Read\fR(\fIchannel, buf, toRead\fR) .sp int \fBTcl_Gets\fR(\fIchannel, lineRead\fR) .sp int \fBTcl_GetsObj\fR(\fIchannel, lineObjPtr\fR) .sp int \fBTcl_Write\fR(\fIchannel, buf, toWrite\fR) .sp int \fBTcl_Flush\fR(\fIchannel\fR) .sp int \fBTcl_Seek\fR(\fIchannel, offset, seekMode\fR) .sp int \fBTcl_Tell\fR(\fIchannel\fR) .sp int \fBTcl_GetChannelOption\fR(\fIinterp, channel, optionName, optionValue\fR) .sp int \fBTcl_SetChannelOption\fR(\fIinterp, channel, optionName, newValue\fR) .sp int \fBTcl_Eof\fR(\fIchannel\fR) .sp int \fBTcl_InputBlocked\fR(\fIchannel\fR) .sp int \fBTcl_InputBuffered\fR(\fIchannel\fR) .sp .SH ARGUMENTS .AS Tcl_ChannelType newClientProcPtr in .AP Tcl_Interp *interp in Used for error reporting and to look up a channel registered in it. .AP char *fileName in The name of a local or network file. .AP char *mode in Specifies how the file is to be accessed. May have any of the values allowed for the \fImode\fR argument to the Tcl \fBopen\fR command. For \fBTcl_OpenCommandChannel\fR, may be NULL. .AP 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. .AP int argc in The number of elements in \fIargv\fR. .AP char **argv in Arguments for constructing a command pipeline. These values have the same meaning as the non-switch arguments to the Tcl \fBexec\fR command. .AP int flags in Specifies the disposition of the stdio handles in pipeline: OR-ed combination of \fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, \fBTCL_STDERR\fR, and \fBTCL_ENFORCE_MODE\fR. If \fBTCL_STDIN\fR 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 \fBTCL_STDOUT\fR and \fBTCL_STDERR\fR. If \fBTCL_ENFORCE_MODE\fR is not set, then the pipe can redirect stdio handles to override the stdio handles for which \fBTCL_STDIN\fR, \fBTCL_STDOUT\fR and \fBTCL_STDERR\fR have been set. If it is set, then such redirections cause an error. .VS .AP ClientData handle in Operating system specific handle for I/O to a file. For Unix this is a file descriptor, for Windows it is a HANDLE. .AP int readOrWrite in OR-ed combination of \fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR to indicate what operations are valid on \fIhandle\fR. .VE .AP int *modePtr out Points at an integer variable that will receive an OR-ed combination of \fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR denoting whether the channel is open for reading and writing. .AP Tcl_Channel channel in A Tcl channel for input or output. Must have been the return value from a procedure such as \fBTcl_OpenFileChannel\fR. .AP char *buf in An array of bytes in which to store channel input, or from which to read channel output. .AP int len in The length of the input or output. .AP int atEnd in If nonzero, store the input at the end of the input queue, otherwise store it at the head of the input queue. .AP int toRead in The number of bytes to read from the channel. .AP Tcl_DString *lineRead in 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. .AP Tcl_Obj *linePtrObj in 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. .AP int toWrite in The number of bytes to read from \fIbuf\fR and output to the channel. .AP 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 \fIseekMode\fR. May be either positive or negative. .AP int seekMode in Relative to which point to seek; used with \fIoffset\fR to calculate the new access point for the channel. Legal values are \fBSEEK_SET\fR, \fBSEEK_CUR\fR, and \fBSEEK_END\fR. .AP char *optionName in The name of an option applicable to this channel, such as \fB\-blocking\fR. May have any of the values accepted by the \fBfconfigure\fR command. .AP 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 caller. .AP char *newValue in New value for the option given by \fIoptionName\fR. .BE .SH DESCRIPTION .PP The Tcl channel mechanism provides a device-independent and platform-independent mechanism for performing buffered input and output operations 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 \fBTcl_CreateChannel\fR. The channel mechanism provides a buffering scheme modelled after Unix's standard I/O, and it also allows for nonblocking I/O on channels. .PP 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 \fBTcl_CreateChannel\fR. .SH TCL_OPENFILECHANNEL .PP \fBTcl_OpenFileChannel\fR opens a file specified by \fIfileName\fR and returns a channel handle that can be used to perform input and output on the file. This API is modelled after the \fBfopen\fR procedure of the Unix standard I/O library. The syntax and meaning of all arguments is similar to those given in the Tcl \fBopen\fR command when opening a file. If an error occurs while opening the channel, \fBTcl_OpenFileChannel\fR returns NULL and records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. In addition, if \fIinterp\fR is non-NULL, \fBTcl_OpenFileChannel\fR leaves an error message in \fIinterp->result\fR after any error. .PP The newly created channel is not registered in the supplied interpreter; to register it, use \fBTcl_RegisterChannel\fR, described below. If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was previously closed, the act of creating the new channel also assigns it as a replacement for the standard channel. .SH TCL_OPENCOMMANDCHANNEL .PP \fBTcl_OpenCommandChannel\fR provides a C-level interface to the functions of the \fBexec\fR and \fBopen\fR commands. It creates a sequence of subprocesses specified by the \fIargv\fR and \fIargc\fR arguments and returns a channel that can be used to communicate with these subprocesses. The \fIflags\fR argument indicates what sort of communication will exist with the command pipeline. .PP If the \fBTCL_STDIN\fR flag is set then the standard input for the first subprocess will be tied to the channel: writing to the channel will provide input to the subprocess. If \fBTCL_STDIN\fR is not set, then standard input for the first subprocess will be the same as this application's standard input. If \fBTCL_STDOUT\fR 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 \fBTCL_STDERR\fR 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 application's standard error. If \fBTCL_ENFORCE_MODE\fR is not set, then \fIargc\fR and \fIargv\fR can redirect the stdio handles to override \fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, and \fBTCL_STDERR\fR; if it is set, then it is an error for argc and argv to override stdio channels for which \fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, and \fBTCL_STDERR\fR have been set. .PP If an error occurs while opening the channel, \fBTcl_OpenCommandChannel\fR returns NULL and records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. In addition, \fBTcl_OpenCommandChannel\fR leaves an error message in \fIinterp->result\fR if \fIinterp\fR is not NULL. .PP The newly created channel is not registered in the supplied interpreter; to register it, use \fBTcl_RegisterChannel\fR, described below. If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was previously closed, the act of creating the new channel also assigns it as a replacement for the standard channel. .SH TCL_MAKEFILECHANNEL .PP \fBTcl_MakeFileChannel\fR makes a \fBTcl_Channel\fR from an existing, platform-specific, file handle. The newly created channel is not registered in the supplied interpreter; to register it, use \fBTcl_RegisterChannel\fR, described below. If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was previously closed, the act of creating the new channel also assigns it as a replacement for the standard channel. .SH TCL_GETCHANNEL .PP \fBTcl_GetChannel\fR returns a channel given the \fIchannelName\fR used to create it with \fBTcl_CreateChannel\fR and a pointer to a Tcl interpreter in \fIinterp\fR. If a channel by that name is not registered in that interpreter, the procedure returns NULL. If the \fImode\fR argument is not NULL, it points at an integer variable that will receive an OR-ed combination of \fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR describing whether the channel is open for reading and writing. .SH TCL_REGISTERCHANNEL .PP \fBTcl_RegisterChannel\fR adds a channel to the set of channels accessible in \fIinterp\fR. 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 \fBTcl_CreateChannel\fR. After this call, the channel becomes the property of the interpreter, and the caller should not call \fBTcl_Close\fR for the channel; the channel will be closed automatically when it is unregistered from the interpreter. .PP Code executing outside of any Tcl interpreter can call \fBTcl_RegisterChannel\fR with \fIinterp\fR as NULL, to indicate that it wishes to hold a reference 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 \fBTcl_UnregisterChannel\fR 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. .SH TCL_UNREGISTERCHANNEL .PP \fBTcl_UnregisterChannel\fR removes a channel from the set of channels accessible in \fIinterp\fR. 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. .PP Code not associated with a Tcl interpreter can call \fBTcl_UnregisterChannel\fR with \fIinterp\fR as NULL, to indicate to Tcl that it no longer holds a reference to that channel. If this is the last reference to the channel, it will now be closed. .SH TCL_CLOSE .PP \fBTcl_Close\fR destroys the channel \fIchannel\fR, which must denote a currently open channel. The channel should not be registered in any interpreter when \fBTcl_Close\fR 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. .PP If the channel was closed successfully, \fBTcl_Close\fR returns \fBTCL_OK\fR. If an error occurs, \fBTcl_Close\fR returns \fBTCL_ERROR\fR and records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. If the channel is being closed synchronously and an error occurs during closing of the channel and \fIinterp\fR is not NULL, an error message is left in \fIinterp->result\fR. .PP Note: it is not safe to call \fBTcl_Close\fR on a channel that has been registered using \fBTcl_RegisterChannel\fR; see the documentation for \fBTcl_RegisterChannel\fR, above, for details. If the channel has ever been given as the \fBchan\fR argument in a call to \fBTcl_RegisterChannel\fR, you should instead use \fBTcl_UnregisterChannel\fR, which will internally call \fBTcl_Close\fR when all calls to \fBTcl_RegisterChannel\fR have been matched by corresponding calls to \fBTcl_UnregisterChannel\fR. .SH TCL_READ .PP \fBTcl_Read\fR consumes up to \fItoRead\fR bytes of data from \fIchannel\fR and stores it at \fIbuf\fR. The return value of \fBTcl_Read\fR is the number of characters written at \fIbuf\fR. The buffer produced by \fBTcl_Read\fR is not NULL terminated. Its contents are valid from the zeroth position up to and excluding the position indicated by the return value. If an error occurs, the return value is -1 and \fBTcl_Read\fR records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. .PP The return value may be smaller than the value of \fItoRead\fR, indicating that less data than requested was available, also called a \fIshort read\fR. In blocking mode, this can only happen on an end-of-file. In nonblocking mode, a short read can also occur if there is not enough input currently available: \fBTcl_Read\fR returns a short count rather than waiting for more data. .PP 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 \fBTcl_Eof\fR and \fBTcl_InputBlocked\fR to tell which of these conditions actually occurred. .PP \fBTcl_Read\fR translates platform-specific end-of-line representations into the canonical \fB\en\fR 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 \fBfconfigure\fR command. .SH TCL_GETS AND TCL_GETSOBJ .PP \fBTcl_Gets\fR reads a line of input from a channel and appends all of the characters of the line except for the terminating end-of-line character(s) to the dynamic string given by \fIdsPtr\fR. The end-of-line character(s) are read and discarded. .PP If a line was successfully read, the return value is greater than or equal to zero, and it indicates the number of characters stored in the dynamic string. If an error occurs, \fBTcl_Gets\fR returns -1 and records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. \fBTcl_Gets\fR also returns -1 if the end of the file is reached; the \fBTcl_Eof\fR procedure can be used to distinguish an error from an end-of-file condition. .PP 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 \fBTcl_InputBlocked\fR procedure may be invoked to determine if the channel is blocked because of input unavailability. .PP \fBTcl_GetsObj\fR is the same as \fBTcl_Gets\fR except the resulting characters are appended to a Tcl object \fBlineObjPtr\fR rather than a dynamic string. .SH TCL_WRITE .PP \fBTcl_Write\fR accepts \fItoWrite\fR bytes of data at \fIbuf\fR for output on \fIchannel\fR. This data may not appear on the output device immediately. If the data should appear immediately, call \fBTcl_Flush\fR after the call to \fBTcl_Write\fR, or set the \fB-buffering\fR option on the channel to \fBnone\fR. If you wish the data to appear as soon as an end of line is accepted for output, set the \fB\-buffering\fR option on the channel to \fBline\fR mode. .PP The \fItoWrite\fR argument specifies how many bytes of data are provided in the \fIbuf\fR argument. If it is negative, \fBTcl_Write\fR expects the data to be NULL terminated and it outputs everything up to the NULL. .PP The return value of \fBTcl_Write\fR is a count of how many characters were accepted for output to the channel. This is either equal to \fItoWrite\fR or -1 to indicate that an error occurred. If an error occurs, \fBTcl_Write\fR also records a POSIX error code that may be retrieved with \fBTcl_GetErrno\fR. .PP Newline characters in the output data are translated to platform-specific end-of-line sequences according to the \fB\-translation\fR option for the channel. .SH TCL_FLUSH .PP \fBTcl_Flush\fR causes all of the buffered output data for \fIchannel\fR 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 eventually, as fast as the channel is able to absorb it. .PP The return value is normally \fBTCL_OK\fR. If an error occurs, \fBTcl_Flush\fR returns \fBTCL_ERROR\fR and records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. .SH TCL_SEEK .PP \fBTcl_Seek\fR moves the access point in \fIchannel\fR 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. .PP \fBTcl_Seek\fR normally returns the new access point. If an error occurs, \fBTcl_Seek\fR returns -1 and records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR. After an error, the access point may or may not have been moved. .SH TCL_TELL .PP \fBTcl_Tell\fR returns the current access point for a channel. The returned value is -1 if the channel does not support seeking. .SH TCL_GETCHANNELOPTION .PP \fBTcl_GetChannelOption\fR retrieves, in \fIdsPtr\fR, the value of one of the options currently in effect for a channel, or a list of all options and their values. The \fIchannel\fR argument identifies the channel for which to query an option or retrieve all options and their values. If \fIoptionName\fR 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 \fIoptionValue\fR. If \fIoptionName\fR is NULL, the function stores an alternating list of option names and their values in \fIoptionValue\fR, using a series of calls to \fBTcl_DStringAppendElement\fR. The various preexisting options and their possible values are described in the manual entry for the Tcl \fBfconfigure\fR 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 additional options for TCP based channels are described in the manual entry for the Tcl \fBsocket\fR command. The procedure normally returns \fBTCL_OK\fR. If an error occurs, it returns \fBTCL_ERROR\fR and calls \fBTcl_SetErrno\fR to store an appropriate POSIX error code. .SH TCL_SETCHANNELOPTION .PP \fBTcl_SetChannelOption\fR sets a new value for an option on \fIchannel\fR. \fIOptionName\fR is the option to set and \fInewValue\fR is the value to set. The procedure normally returns \fBTCL_OK\fR. If an error occurs, it returns \fBTCL_ERROR\fR; in addition, if \fIinterp\fR is non-NULL, \fBTcl_SetChannelOption\fR leaves an error message in \fIinterp->result\fR. .SH TCL_EOF .PP \fBTcl_Eof\fR returns a nonzero value if \fIchannel\fR encountered an end of file during the last input operation. .SH TCL_INPUTBLOCKED .PP \fBTcl_InputBlocked\fR returns a nonzero value if \fIchannel\fR 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. .SH TCL_INPUTBUFFERED .PP \fBTcl_InputBuffered\fR 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. .VS .SH "PLATFORM ISSUES" .PP The handles returned from \fBTcl_GetChannelHandle\fR depend on the platform and the channel type. On Unix platforms, the handle is always a Unix file descriptor as returned from the \fBopen\fR system call. On Windows platforms, the handle is a file \fBHANDLE\fR when the channel was created with \fBTcl_OpenFileChannel\fR, \fBTcl_OpenCommandChannel\fR, or \fBTcl_MakeFileChannel\fR. Other channel types may return a different type of handle on Windows platforms. On the Macintosh platform, the handle is a file reference number as returned from \fBHOpenDF\fR. .VE .SH "SEE ALSO" DString(3), fconfigure(n), filename(n), fopen(2), Tcl_CreateChannel(3) .SH KEYWORDS access point, blocking, buffered I/O, channel, channel driver, end of file, flush, input, nonblocking, output, read, seek, write