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173 lines
4.8 KiB
Groff
173 lines
4.8 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)funopen.3 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd June 9, 1993
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.Dt FUNOPEN 3
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.Os
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.Sh NAME
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.Nm funopen ,
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.Nm fropen ,
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.Nm fwopen
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.Nd open a stream
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <stdio.h>
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.Ft FILE *
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.Fn funopen "const void *cookie" "int (*readfn)(void *, char *, int)" "int (*writefn)(void *, const char *, int)" "fpos_t (*seekfn)(void *, fpos_t, int)" "int (*closefn)(void *)"
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.Ft FILE *
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.Fn fropen "void *cookie" "int (*readfn)(void *, char *, int)"
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.Ft FILE *
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.Fn fwopen "void *cookie" "int (*writefn)(void *, const char *, int)"
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.Sh DESCRIPTION
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The
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.Fn funopen
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function
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associates a stream with up to four
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.Dq Tn I/O No functions .
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Either
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.Fa readfn
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or
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.Fa writefn
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must be specified;
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the others can be given as an appropriately-typed
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.Dv NULL
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pointer.
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These
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.Tn I/O
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functions will be used to read, write, seek and
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close the new stream.
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.Pp
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In general, omitting a function means that any attempt to perform the
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associated operation on the resulting stream will fail.
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If the close function is omitted, closing the stream will flush
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any buffered output and then succeed.
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.Pp
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The calling conventions of
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.Fa readfn ,
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.Fa writefn ,
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.Fa seekfn
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and
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.Fa closefn
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must match those, respectively, of
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.Xr read 2 ,
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.Xr write 2 ,
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.Xr lseek 2 ,
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and
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.Xr close 2
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with the single exception that they are passed the
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.Fa cookie
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argument specified to
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.Fn funopen
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in place of the traditional file descriptor argument.
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.Pp
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Read and write
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.Tn I/O
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functions are allowed to change the underlying buffer
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on fully buffered or line buffered streams by calling
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.Xr setvbuf 3 .
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They are also not required to completely fill or empty the buffer.
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They are not, however, allowed to change streams from unbuffered to buffered
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or to change the state of the line buffering flag.
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They must also be prepared to have read or write calls occur on buffers other
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than the one most recently specified.
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.Pp
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All user
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.Tn I/O
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functions can report an error by returning \-1.
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Additionally, all of the functions should set the external variable
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.Va errno
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appropriately if an error occurs.
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.Pp
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An error on
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.Fn closefn
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does not keep the stream open.
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.Pp
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As a convenience, the include file
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.Aq Pa stdio.h
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defines the macros
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.Fn fropen
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and
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.Fn fwopen
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as calls to
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.Fn funopen
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with only a read or write function specified.
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn funopen
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returns a
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.Dv FILE
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pointer.
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Otherwise,
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.Dv NULL
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is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fn funopen
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function
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was called without either a read or write function.
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The
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.Fn funopen
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function
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may also fail and set
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.Va errno
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for any of the errors
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specified for the routine
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.Xr malloc 3 .
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.El
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.Sh SEE ALSO
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.Xr fcntl 2 ,
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.Xr open 2 ,
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.Xr fclose 3 ,
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.Xr fopen 3 ,
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.Xr fseek 3 ,
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.Xr setbuf 3
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.Sh HISTORY
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The
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.Fn funopen
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functions first appeared in
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.Bx 4.4 .
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.Sh BUGS
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The
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.Fn funopen
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function
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may not be portable to systems other than
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.Bx .
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