1.\" $NetBSD: funopen.3,v 1.15 2010/03/22 19:30:54 joerg Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" Chris Torek. 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)funopen.3 8.1 (Berkeley) 6/9/93 33.\" 34.Dd June 9, 1993 35.Dt FUNOPEN 3 36.Os 37.Sh NAME 38.Nm funopen , 39.Nm fropen , 40.Nm fwopen 41.Nd open a stream 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In stdio.h 46.Ft FILE * 47.Fn funopen "void *cookie" "int (*readfn)(void *, char *, int)" "int (*writefn)(void *, const char *, int)" "fpos_t (*seekfn)(void *, fpos_t, int)" "int (*closefn)(void *)" 48.Ft FILE * 49.Fn fropen "void *cookie" "int (*readfn)(void *, char *, int)" 50.Ft FILE * 51.Fn fwopen "void *cookie" "int (*writefn)(void *, const char *, int)" 52.Sh DESCRIPTION 53The 54.Fn funopen 55function 56associates a stream with up to four 57.Dq Tn I/O No functions . 58Either 59.Fa readfn 60or 61.Fa writefn 62must be specified; 63the others can be given as an appropriately-typed 64.Dv NULL 65pointer. 66These 67.Tn I/O 68functions will be used to read, write, seek and 69close the new stream. 70.Pp 71In general, omitting a function means that any attempt to perform the 72associated operation on the resulting stream will fail. 73If the close function is omitted, closing the stream will flush 74any buffered output and then succeed. 75.Pp 76The calling conventions of 77.Fa readfn , 78.Fa writefn , 79.Fa seekfn 80and 81.Fa closefn 82must match those, respectively, of 83.Xr read 2 , 84.Xr write 2 , 85.Xr lseek 2 , 86and 87.Xr close 2 ; 88except that they are passed the 89.Fa cookie 90argument specified to 91.Fn funopen 92in place of the traditional file descriptor argument, 93and 94.Fa seekfn 95uses 96.Li fpos_t 97instead of 98.Li off_t . 99.Pp 100Read and write 101.Tn I/O 102functions are allowed to change the underlying buffer 103on fully buffered or line buffered streams by calling 104.Xr setvbuf 3 . 105They are also not required to completely fill or empty the buffer. 106They are not, however, allowed to change streams from unbuffered to buffered 107or to change the state of the line buffering flag. 108They must also be prepared to have read or write calls occur on buffers other 109than the one most recently specified. 110.Pp 111All user 112.Tn I/O 113functions can report an error by returning \-1. 114Additionally, all of the functions should set the external variable 115.Va errno 116appropriately if an error occurs. 117.Pp 118An error on 119.Fn closefn 120does not keep the stream open. 121.Pp 122As a convenience, the include file 123.In stdio.h 124defines the macros 125.Fn fropen 126and 127.Fn fwopen 128as calls to 129.Fn funopen 130with only a read or write function specified. 131.Sh RETURN VALUES 132Upon successful completion, 133.Fn funopen 134returns a 135.Dv FILE 136pointer. 137Otherwise, 138.Dv NULL 139is returned and the global variable 140.Va errno 141is set to indicate the error. 142.Sh ERRORS 143.Bl -tag -width Er 144.It Bq Er EINVAL 145The 146.Fn funopen 147function 148was called without either a read or write function. 149The 150.Fn funopen 151function 152may also fail and set 153.Va errno 154for any of the errors 155specified for the routine 156.Xr malloc 3 . 157.El 158.Sh SEE ALSO 159.Xr fcntl 2 , 160.Xr open 2 , 161.Xr fclose 3 , 162.Xr fopen 3 , 163.Xr fseek 3 , 164.Xr setbuf 3 165.Sh HISTORY 166The 167.Fn funopen 168functions first appeared in 169.Bx 4.4 . 170.Sh BUGS 171The 172.Fn funopen 173function 174may not be portable to systems other than 175.Bx . 176