[apple/libc.git] / stdio / FreeBSD / funopen.3

.\" Copyright (c) 1990, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek.
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)funopen.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: src/lib/libc/stdio/funopen.3,v 1.16 2007/01/09 00:28:06 imp Exp $
.\"
.Dd March 19, 2004
.Dt FUNOPEN 3
.Os
.Sh NAME
.Nm funopen ,
.Nm fropen ,
.Nm fwopen
.Nd open a stream
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft FILE *
.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 *)"
.Ft FILE *
.Fn fropen "void *cookie" "int (*readfn)(void *, char *, int)"
.Ft FILE *
.Fn fwopen "void *cookie" "int (*writefn)(void *, const char *, int)"
.Sh DESCRIPTION
The
.Fn funopen
function
associates a stream with up to four
.Dq Tn I/O No functions .
Either
.Fa readfn
or
.Fa writefn
must be specified;
the others can be given as an appropriately-typed
.Dv NULL
pointer.
These
.Tn I/O
functions will be used to read, write, seek and
close the new stream.
.Pp
In general, omitting a function means that any attempt to perform the
associated operation on the resulting stream will fail.
If the close function is omitted, closing the stream will flush
any buffered output and then succeed.
.Pp
The calling conventions of
.Fa readfn ,
.Fa writefn ,
.Fa seekfn
and
.Fa closefn
must match those, respectively, of
.Xr read 2 ,
.Xr write 2 ,
.Xr lseek 2 ,
and
.Xr close 2
with the single exception that they are passed the
.Fa cookie
argument specified to
.Fn funopen
in place of the traditional file descriptor argument.
.Pp
Read and write
.Tn I/O
functions are allowed to change the underlying buffer
on fully buffered or line buffered streams by calling
.Xr setvbuf 3 .
They are also not required to completely fill or empty the buffer.
They are not, however, allowed to change streams from unbuffered to buffered
or to change the state of the line buffering flag.
They must also be prepared to have read or write calls occur on buffers other
than the one most recently specified.
.Pp
All user
.Tn I/O
functions can report an error by returning \-1.
Additionally, all of the functions should set the external variable
.Va errno
appropriately if an error occurs.
.Pp
An error on
.Fn closefn
does not keep the stream open.
.Pp
As a convenience, the include file
.In stdio.h
defines the macros
.Fn fropen
and
.Fn fwopen
as calls to
.Fn funopen
with only a read or write function specified.
.Sh RETURN VALUES
Upon successful completion,
.Fn funopen
returns a
.Dv FILE
pointer.
Otherwise,
.Dv NULL
is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fn funopen
function
was called without either a read or write function.
The
.Fn funopen
function
may also fail and set
.Va errno
for any of the errors
specified for the routine
.Xr malloc 3 .
.El
.Sh SEE ALSO
.Xr fcntl 2 ,
.Xr open 2 ,
.Xr fclose 3 ,
.Xr fopen 3 ,
.Xr fseek 3 ,
.Xr setbuf 3
.Sh HISTORY
The
.Fn funopen
functions first appeared in
.Bx 4.4 .
.Sh BUGS
The
.Fn funopen
function
may not be portable to systems other than
.Bx .
.Pp
The
.Fn funopen
interface erroneously assumes that
.Vt fpos_t
is an integral type; see
.Xr fseek 3
for a discussion of this issue.
Commit	Line	Data
5b2abdfb A	1	.\" Copyright (c) 1990, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" Chris Torek.
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
5b2abdfb A	14	.\" 4. Neither the name of the University nor the names of its contributors
	15	.\" may be used to endorse or promote products derived from this software
	16	.\" without specific prior written permission.
	17	.\"
	18	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	19	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	20	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	21	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	22	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	23	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	24	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	25	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	26	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	27	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	28	.\" SUCH DAMAGE.
	29	.\"
	30	.\" @(#)funopen.3 8.1 (Berkeley) 6/9/93
1f2f436a	31	.\" $FreeBSD: src/lib/libc/stdio/funopen.3,v 1.16 2007/01/09 00:28:06 imp Exp $
5b2abdfb	32	.\"
3d9156a7	33	.Dd March 19, 2004
5b2abdfb A	34	.Dt FUNOPEN 3
	35	.Os
	36	.Sh NAME
	37	.Nm funopen ,
	38	.Nm fropen ,
	39	.Nm fwopen
	40	.Nd open a stream
	41	.Sh LIBRARY
	42	.Lb libc
	43	.Sh SYNOPSIS
	44	.In stdio.h
	45	.Ft FILE *
	46	.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 *)"
	47	.Ft FILE *
3d9156a7	48	.Fn fropen "void cookie" "int (readfn)(void , char , int)"
5b2abdfb	49	.Ft FILE *
3d9156a7	50	.Fn fwopen "void cookie" "int (writefn)(void , const char , int)"
5b2abdfb A	51	.Sh DESCRIPTION
	52	The
	53	.Fn funopen
	54	function
	55	associates a stream with up to four
	56	.Dq Tn I/O No functions .
	57	Either
	58	.Fa readfn
	59	or
	60	.Fa writefn
	61	must be specified;
	62	the others can be given as an appropriately-typed
	63	.Dv NULL
	64	pointer.
	65	These
	66	.Tn I/O
	67	functions will be used to read, write, seek and
	68	close the new stream.
	69	.Pp
	70	In general, omitting a function means that any attempt to perform the
	71	associated operation on the resulting stream will fail.
	72	If the close function is omitted, closing the stream will flush
	73	any buffered output and then succeed.
	74	.Pp
	75	The calling conventions of
	76	.Fa readfn ,
	77	.Fa writefn ,
	78	.Fa seekfn
	79	and
	80	.Fa closefn
	81	must match those, respectively, of
	82	.Xr read 2 ,
	83	.Xr write 2 ,
	84	.Xr lseek 2 ,
	85	and
	86	.Xr close 2
	87	with the single exception that they are passed the
	88	.Fa cookie
	89	argument specified to
	90	.Fn funopen
	91	in place of the traditional file descriptor argument.
	92	.Pp
	93	Read and write
	94	.Tn I/O
	95	functions are allowed to change the underlying buffer
	96	on fully buffered or line buffered streams by calling
	97	.Xr setvbuf 3 .
	98	They are also not required to completely fill or empty the buffer.
	99	They are not, however, allowed to change streams from unbuffered to buffered
	100	or to change the state of the line buffering flag.
	101	They must also be prepared to have read or write calls occur on buffers other
	102	than the one most recently specified.
	103	.Pp
	104	All user
	105	.Tn I/O
	106	functions can report an error by returning \-1.
	107	Additionally, all of the functions should set the external variable
	108	.Va errno
	109	appropriately if an error occurs.
	110	.Pp
	111	An error on
	112	.Fn closefn
	113	does not keep the stream open.
	114	.Pp
115	As a convenience, the include file
3d9156a7	116	.In stdio.h
5b2abdfb A	117	defines the macros
	118	.Fn fropen
	119	and
	120	.Fn fwopen
	121	as calls to
	122	.Fn funopen
	123	with only a read or write function specified.
	124	.Sh RETURN VALUES
	125	Upon successful completion,
	126	.Fn funopen
	127	returns a
	128	.Dv FILE
	129	pointer.
	130	Otherwise,
	131	.Dv NULL
	132	is returned and the global variable
	133	.Va errno
	134	is set to indicate the error.
	135	.Sh ERRORS
	136	.Bl -tag -width Er
	137	.It Bq Er EINVAL
	138	The
	139	.Fn funopen
	140	function
	141	was called without either a read or write function.
	142	The
	143	.Fn funopen
	144	function
	145	may also fail and set
	146	.Va errno
	147	for any of the errors
	148	specified for the routine
	149	.Xr malloc 3 .
	150	.El
	151	.Sh SEE ALSO
	152	.Xr fcntl 2 ,
	153	.Xr open 2 ,
	154	.Xr fclose 3 ,
	155	.Xr fopen 3 ,
	156	.Xr fseek 3 ,
	157	.Xr setbuf 3
	158	.Sh HISTORY
	159	The
	160	.Fn funopen
	161	functions first appeared in
	162	.Bx 4.4 .
	163	.Sh BUGS
	164	The
	165	.Fn funopen
	166	function
	167	may not be portable to systems other than
	168	.Bx .
3d9156a7 A	169	.Pp
	170	The
	171	.Fn funopen
	172	interface erroneously assumes that
	173	.Vt fpos_t
	174	is an integral type; see
	175	.Xr fseek 3
	176	for a discussion of this issue.