[apple/libc.git] / stdio / FreeBSD / fgets.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 and the American National Standards Committee X3,
.\" on Information Processing Systems.
.\"
.\" 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.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 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.
.\"
.\"     @(#)fgets.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/stdio/fgets.3,v 1.19 2002/12/04 18:57:45 ru Exp $
.\"
.Dd June 4, 1993
.Dt FGETS 3
.Os
.Sh NAME
.Nm fgets ,
.Nm gets
.Nd get a line from a stream
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft char *
.Fn fgets "char * restrict str" "int size" "FILE * restrict stream"
.Ft char *
.Fn gets "char *str"
.Sh DESCRIPTION
The
.Fn fgets
function
reads at most one less than the number of characters specified by
.Fa size
from the given
.Fa stream
and stores them in the string
.Fa str .
Reading stops when a newline character is found,
at end-of-file or error.
The newline, if any, is retained.
If any characters are read and there is no error, a
.Ql \e0
character is appended to end the string.
.Pp
The
.Fn gets
function
is equivalent to
.Fn fgets
with an infinite
.Fa size
and a
.Fa stream
of
.Dv stdin ,
except that the newline character (if any) is not stored in the string.
It is the caller's responsibility to ensure that the input line,
if any, is sufficiently short to fit in the string.
.Sh RETURN VALUES
Upon successful completion,
.Fn fgets
and
.Fn gets
return
a pointer to the string.
If end-of-file occurs before any characters are read,
they return
.Dv NULL
and the buffer contents remain unchanged.
If an error occurs,
they return
.Dv NULL
and the buffer contents are indeterminate.
The
.Fn fgets
and
.Fn gets
functions
do not distinguish between end-of-file and error, and callers must use
.Xr feof 3
and
.Xr ferror 3
to determine which occurred.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EBADF
The given
.Fa stream
is not a readable stream.
.El
.Pp
The function
.Fn fgets
may also fail and set
.Va errno
for any of the errors specified for the routines
.Xr fflush 3 ,
.Xr fstat 2 ,
.Xr read 2 ,
or
.Xr malloc 3 .
.Pp
The function
.Fn gets
may also fail and set
.Va errno
for any of the errors specified for the routine
.Xr getchar 3 .
.Sh SECURITY CONSIDERATIONS
The
.Fn gets
function cannot be used securely.
Because of its lack of bounds checking,
and the inability for the calling program
to reliably determine the length of the next incoming line,
the use of this function enables malicious users
to arbitrarily change a running program's functionality through
a buffer overflow attack.
It is strongly suggested that the
.Fn fgets
function be used in all cases.
(See
the FSA.)
.Sh SEE ALSO
.Xr feof 3 ,
.Xr ferror 3 ,
.Xr fgetln 3 ,
.Xr fgetws 3
.Rs
.%T "The FreeBSD Security Architecture"
.Re
(See
.Pa /usr/share/doc/{to be determined} . )
.Sh STANDARDS
The functions
.Fn fgets
and
.Fn gets
conform to
.St -isoC-99 .
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 and the American National Standards Committee X3,
	6	.\" on Information Processing Systems.
	7	.\"
	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. All advertising materials mentioning features or use of this software
	17	.\" must display the following acknowledgement:
	18	.\" This product includes software developed by the University of
	19	.\" California, Berkeley and its contributors.
	20	.\" 4. Neither the name of the University nor the names of its contributors
	21	.\" may be used to endorse or promote products derived from this software
	22	.\" without specific prior written permission.
	23	.\"
	24	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	25	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	26	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	27	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	28	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	29	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	30	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	31	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	32	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	33	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	34	.\" SUCH DAMAGE.
	35	.\"
	36	.\" @(#)fgets.3 8.1 (Berkeley) 6/4/93
9385eb3d	37	.\" $FreeBSD: src/lib/libc/stdio/fgets.3,v 1.19 2002/12/04 18:57:45 ru Exp $
5b2abdfb A	38	.\"
	39	.Dd June 4, 1993
	40	.Dt FGETS 3
	41	.Os
	42	.Sh NAME
	43	.Nm fgets ,
	44	.Nm gets
	45	.Nd get a line from a stream
	46	.Sh LIBRARY
	47	.Lb libc
	48	.Sh SYNOPSIS
	49	.In stdio.h
	50	.Ft char *
9385eb3d	51	.Fn fgets "char * restrict str" "int size" "FILE * restrict stream"
5b2abdfb A	52	.Ft char *
	53	.Fn gets "char *str"
	54	.Sh DESCRIPTION
	55	The
	56	.Fn fgets
	57	function
	58	reads at most one less than the number of characters specified by
	59	.Fa size
	60	from the given
	61	.Fa stream
	62	and stores them in the string
	63	.Fa str .
	64	Reading stops when a newline character is found,
	65	at end-of-file or error.
	66	The newline, if any, is retained.
	67	If any characters are read and there is no error, a
	68	.Ql \e0
	69	character is appended to end the string.
	70	.Pp
	71	The
	72	.Fn gets
	73	function
	74	is equivalent to
	75	.Fn fgets
	76	with an infinite
	77	.Fa size
	78	and a
	79	.Fa stream
	80	of
9385eb3d	81	.Dv stdin ,
5b2abdfb A	82	except that the newline character (if any) is not stored in the string.
	83	It is the caller's responsibility to ensure that the input line,
	84	if any, is sufficiently short to fit in the string.
	85	.Sh RETURN VALUES
	86	Upon successful completion,
	87	.Fn fgets
	88	and
	89	.Fn gets
	90	return
	91	a pointer to the string.
	92	If end-of-file occurs before any characters are read,
	93	they return
	94	.Dv NULL
9385eb3d	95	and the buffer contents remain unchanged.
5b2abdfb A	96	If an error occurs,
	97	they return
	98	.Dv NULL
9385eb3d	99	and the buffer contents are indeterminate.
5b2abdfb A	100	The
	101	.Fn fgets
	102	and
	103	.Fn gets
	104	functions
	105	do not distinguish between end-of-file and error, and callers must use
	106	.Xr feof 3
	107	and
	108	.Xr ferror 3
	109	to determine which occurred.
	110	.Sh ERRORS
	111	.Bl -tag -width Er
	112	.It Bq Er EBADF
	113	The given
	114	.Fa stream
	115	is not a readable stream.
	116	.El
	117	.Pp
	118	The function
	119	.Fn fgets
	120	may also fail and set
	121	.Va errno
	122	for any of the errors specified for the routines
	123	.Xr fflush 3 ,
	124	.Xr fstat 2 ,
	125	.Xr read 2 ,
	126	or
	127	.Xr malloc 3 .
	128	.Pp
	129	The function
	130	.Fn gets
	131	may also fail and set
	132	.Va errno
	133	for any of the errors specified for the routine
	134	.Xr getchar 3 .
9385eb3d A	135	.Sh SECURITY CONSIDERATIONS
	136	The
	137	.Fn gets
	138	function cannot be used securely.
	139	Because of its lack of bounds checking,
	140	and the inability for the calling program
	141	to reliably determine the length of the next incoming line,
	142	the use of this function enables malicious users
	143	to arbitrarily change a running program's functionality through
	144	a buffer overflow attack.
	145	It is strongly suggested that the
	146	.Fn fgets
	147	function be used in all cases.
	148	(See
	149	the FSA.)
5b2abdfb A	150	.Sh SEE ALSO
	151	.Xr feof 3 ,
	152	.Xr ferror 3 ,
9385eb3d A	153	.Xr fgetln 3 ,
	154	.Xr fgetws 3
	155	.Rs
	156	.%T "The FreeBSD Security Architecture"
	157	.Re
	158	(See
	159	.Pa /usr/share/doc/{to be determined} . )
5b2abdfb A	160	.Sh STANDARDS
	161	The functions
	162	.Fn fgets
	163	and
	164	.Fn gets
	165	conform to
9385eb3d	166	.St -isoC-99 .