[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.
.\" 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 1.22 2009/02/28 06:00:58 das 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 ,
.Xr getline 3
.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.
5b2abdfb A	16	.\" 4. 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	.\" @(#)fgets.3 8.1 (Berkeley) 6/4/93
1f2f436a	33	.\" $FreeBSD: src/lib/libc/stdio/fgets.3,v 1.22 2009/02/28 06:00:58 das Exp $
5b2abdfb A	34	.\"
	35	.Dd June 4, 1993
	36	.Dt FGETS 3
	37	.Os
	38	.Sh NAME
	39	.Nm fgets ,
	40	.Nm gets
	41	.Nd get a line from a stream
	42	.Sh LIBRARY
	43	.Lb libc
	44	.Sh SYNOPSIS
	45	.In stdio.h
	46	.Ft char *
9385eb3d	47	.Fn fgets "char * restrict str" "int size" "FILE * restrict stream"
5b2abdfb A	48	.Ft char *
	49	.Fn gets "char *str"
	50	.Sh DESCRIPTION
	51	The
	52	.Fn fgets
	53	function
	54	reads at most one less than the number of characters specified by
	55	.Fa size
	56	from the given
	57	.Fa stream
	58	and stores them in the string
	59	.Fa str .
	60	Reading stops when a newline character is found,
	61	at end-of-file or error.
	62	The newline, if any, is retained.
	63	If any characters are read and there is no error, a
	64	.Ql \e0
	65	character is appended to end the string.
	66	.Pp
	67	The
	68	.Fn gets
	69	function
	70	is equivalent to
	71	.Fn fgets
	72	with an infinite
	73	.Fa size
	74	and a
	75	.Fa stream
	76	of
9385eb3d	77	.Dv stdin ,
5b2abdfb A	78	except that the newline character (if any) is not stored in the string.
	79	It is the caller's responsibility to ensure that the input line,
	80	if any, is sufficiently short to fit in the string.
	81	.Sh RETURN VALUES
	82	Upon successful completion,
	83	.Fn fgets
	84	and
	85	.Fn gets
	86	return
	87	a pointer to the string.
	88	If end-of-file occurs before any characters are read,
	89	they return
	90	.Dv NULL
9385eb3d	91	and the buffer contents remain unchanged.
5b2abdfb A	92	If an error occurs,
	93	they return
	94	.Dv NULL
9385eb3d	95	and the buffer contents are indeterminate.
5b2abdfb A	96	The
	97	.Fn fgets
	98	and
	99	.Fn gets
	100	functions
	101	do not distinguish between end-of-file and error, and callers must use
	102	.Xr feof 3
	103	and
	104	.Xr ferror 3
	105	to determine which occurred.
	106	.Sh ERRORS
	107	.Bl -tag -width Er
	108	.It Bq Er EBADF
	109	The given
	110	.Fa stream
	111	is not a readable stream.
	112	.El
	113	.Pp
	114	The function
	115	.Fn fgets
	116	may also fail and set
	117	.Va errno
	118	for any of the errors specified for the routines
	119	.Xr fflush 3 ,
	120	.Xr fstat 2 ,
	121	.Xr read 2 ,
	122	or
	123	.Xr malloc 3 .
	124	.Pp
	125	The function
	126	.Fn gets
	127	may also fail and set
	128	.Va errno
	129	for any of the errors specified for the routine
	130	.Xr getchar 3 .
9385eb3d A	131	.Sh SECURITY CONSIDERATIONS
	132	The
	133	.Fn gets
	134	function cannot be used securely.
	135	Because of its lack of bounds checking,
	136	and the inability for the calling program
	137	to reliably determine the length of the next incoming line,
	138	the use of this function enables malicious users
	139	to arbitrarily change a running program's functionality through
	140	a buffer overflow attack.
	141	It is strongly suggested that the
	142	.Fn fgets
	143	function be used in all cases.
	144	(See
	145	the FSA.)
5b2abdfb A	146	.Sh SEE ALSO
	147	.Xr feof 3 ,
	148	.Xr ferror 3 ,
9385eb3d	149	.Xr fgetln 3 ,
1f2f436a A	150	.Xr fgetws 3 ,
1f2f436a A	151	.Xr getline 3
5b2abdfb A	152	.Sh STANDARDS
	153	The functions
	154	.Fn fgets
	155	and
	156	.Fn gets
	157	conform to
9385eb3d	158	.St -isoC-99 .