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[thirdparty/man-pages.git] / man3 / gets.3

.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
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.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
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.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
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.\" Modified Wed Jul 28 11:12:07 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Fri Sep  8 15:48:13 1995 by Andries Brouwer (aeb@cwi.nl)
.TH GETS 3  2012-01-18 "GNU" "Linux Programmer's Manual"
.SH NAME
fgetc, fgets, getc, getchar, gets, ungetc \- input of characters and strings
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.sp
.BI "int fgetc(FILE *" stream );

.BI "char *fgets(char *" "s" ", int " "size" ", FILE *" "stream" );

.BI "int getc(FILE *" stream );

.B "int getchar(void);"

.BI "char *gets(char *" "s" );

.BI "int ungetc(int " c ", FILE *" stream );
.fi
.SH DESCRIPTION
.BR fgetc ()
reads the next character from
.I stream
and returns it as an
.I unsigned char
cast to an
.IR int ,
or
.B EOF
on end of file or error.
.PP
.BR getc ()
is equivalent to
.BR fgetc ()
except that it may be implemented as a macro which evaluates
.I stream
more than once.
.PP
.BR getchar ()
is equivalent to
.BI "getc(" stdin ) \fR.
.PP
.BR gets ()
reads a line from
.I stdin
into the buffer pointed to by
.I s
until either a terminating newline or
.BR EOF ,
which it replaces with a null byte (\(aq\\0\(aq).
No check for buffer overrun is performed (see BUGS below).
.PP
.BR fgets ()
reads in at most one less than
.I size
characters from
.I stream
and stores them into the buffer pointed to by
.IR s .
Reading stops after an
.B EOF
or a newline.
If a newline is read, it is stored into the buffer.
A terminating null byte (\(aq\\0\(aq)
is stored after the last character in the buffer.
.PP
.BR ungetc ()
pushes
.I c
back to
.IR stream ,
cast to
.IR "unsigned char" ,
where it is available for subsequent read operations.
Pushed-back characters
will be returned in reverse order; only one pushback is guaranteed.
.PP
Calls to the functions described here can be mixed with each other and with
calls to other input functions from the
.I stdio
library for the same input stream.
.PP
For nonlocking counterparts, see
.BR unlocked_stdio (3).
.SH "RETURN VALUE"
.BR fgetc (),
.BR getc ()
and
.BR getchar ()
return the character read as an
.I unsigned char
cast to an
.I int
or
.B EOF
on end of file or error.
.PP
.BR gets ()
and
.BR fgets ()
return
.I s
on success, and NULL
on error or when end of file occurs while no characters have been read.
.PP
.BR ungetc ()
returns
.I c
on success, or
.B EOF
on error.
.SH "CONFORMING TO"
C89, C99, POSIX.1-2001.

LSB deprecates
.BR gets ().
POSIX.1-2008 marks
.BR gets ()
obsolescent.
ISO C11 removes the specification of
.BR gets ()
from the C language, and since version 2.16,
glibc header files don't expose the function declaration if the
.B _ISOC11_SOURCE
feature test macro is defined.
.SH BUGS
Never use
.BR gets ().
Because it is impossible to tell without knowing the data in advance how many
characters
.BR gets ()
will read, and because
.BR gets ()
will continue to store characters past the end of the buffer,
it is extremely dangerous to use.
It has been used to break computer security.
Use
.BR fgets ()
instead.
.PP
It is not advisable to mix calls to input functions from the
.I stdio
library with low-level calls to
.BR read (2)
for the file descriptor associated with the input stream; the results
will be undefined and very probably not what you want.
.SH "SEE ALSO"
.BR read (2),
.BR write (2),
.BR ferror (3),
.BR fgetwc (3),
.BR fgetws (3),
.BR fopen (3),
.BR fread (3),
.BR fseek (3),
.BR getline (3),
.BR getwchar (3),
.BR puts (3),
.BR scanf (3),
.BR ungetwc (3),
.BR unlocked_stdio (3),
.BR feature_test_macros (7)