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.\"     @(#)stdio.3	6.5 (Berkeley) 5/6/91
.\"
.\" Converted for Linux, Mon Nov 29 16:07:22 1993, faith@cs.unc.edu
.\" Modified, 2001-12-26, aeb
.\"
.TH STDIO 3  2001-12-26 "" "Linux Programmer's Manual"
.SH NAME
stdio \- standard input/output library functions
.SH SYNOPSIS
.B #include <stdio.h>
.sp
.BI "FILE *" stdin ;
.br
.BI "FILE *" stdout ;
.br
.BI "FILE *" stderr ;
.SH DESCRIPTION
The standard I/O library provides a simple and efficient buffered stream
I/O interface.
Input and output is mapped into logical data streams and the
physical I/O characteristics are concealed.
The functions and macros are
listed below; more information is available from the individual man pages.
.PP
A stream is associated with an external file (which may be a physical
device) by
.I opening
a file, which may involve creating a new file.
Creating an existing file
causes its former contents to be discarded.
If a file can support positioning requests (such as a disk file,
as opposed to a terminal), then a
.I file position indicator
associated with the stream is positioned at the start of the file (byte
zero), unless the file is opened with append mode.
If append mode is used,
it is unspecified whether the position indicator will be placed at the
start or the end of the file.
The position indicator is maintained by
subsequent reads, writes and positioning requests.
All input occurs as if the characters were read by successive calls to the
.BR fgetc (3)
function; all output takes place as if all characters were written by
successive calls to the
.BR fputc (3)
function.
.PP
A file is disassociated from a stream by
.I closing
the file.
Output streams are flushed (any unwritten buffer contents are
transferred to the host environment) before the stream is disassociated from
the file.
The value of a pointer to a
.I FILE
object is indeterminate after a file is closed (garbage).
.PP
A file may be subsequently reopened, by the same or another program
execution, and its contents reclaimed or modified (if it can be
repositioned at the start).
If the main function returns to its original
caller, or the
.BR exit (3)
function is called, all open files are closed (hence all output streams are
flushed) before program termination.
Other methods of program termination,
such as
.BR abort (3)
do not bother about closing files properly.
.PP
At program startup, three text streams are predefined and need not be
opened explicitly:
.I standard input
(for reading conventional input),
.I standard output
(for writing conventional output), and
.I standard error
(for writing diagnostic output).
These streams are abbreviated
.IR stdin , stdout
and
.IR stderr .
When opened, the standard error stream is not fully buffered; the standard
input and output streams are fully buffered if and only if the streams do
not refer to an interactive device.
.PP
Output streams that refer to terminal devices are always line buffered by
default; pending output to such streams is written automatically whenever
an input stream that refers to a terminal device is read.
In cases where a
large amount of computation is done after printing part of a line on an
output terminal, it is necessary to
.BR fflush (3)
the standard output before going off and computing so that the output will
appear.
.PP
The
.I stdio
library is a part of the library
.B libc
and routines are automatically loaded as needed by the compilers
.BR cc (1)
and
.BR pc (1).
The
SYNOPSIS
sections of the following manual pages indicate which include files are to
be used, what the compiler declaration for the function looks like and
which external variables are of interest.
.PP
The following are defined as macros; these names may not be reused without
first removing their current definitions with
.BR #undef :
.BR BUFSIZ ,
.BR EOF ,
.BR FILENAME_MAX ,
.BR FOPEN_MAX ,
.BR L_cuserid ,
.BR L_ctermid ,
.BR L_tmpnam ,
.BR NULL ,
.BR SEEK_END ,
.BR SEEK_SET ,
.BR SEEK_CUR ,
.BR TMP_MAX ,
.BR clearerr ,
.BR feof ,
.BR ferror ,
.BR fileno ,
.\" Not on Linux: .BR fropen ,
.\" Not on Linux: .BR fwopen ,
.BR getc ,
.BR getchar ,
.BR putc ,
.BR putchar ,
.BR stderr ,
.BR stdin ,
.BR stdout .
Function versions of the macro functions
.BR feof ,
.BR ferror ,
.BR clearerr ,
.BR fileno ,
.BR getc ,
.BR getchar ,
.BR putc ,
and
.B putchar
exist and will be used if the macros definitions are explicitly removed.
.SS List of functions
.TS
;
lb lb
lb l.
Function	Description
_
clearerr	check and reset stream status
fclose	close a stream
fdopen	stream open functions
feof	check and reset stream status
ferror	check and reset stream status
fflush	flush a stream
fgetc	get next character or word from input stream
fgetpos	reposition a stream
fgets	get a line from a stream
fileno	return the integer descriptor of the argument stream
fopen	stream open functions
fprintf	formatted output conversion
fpurge	flush a stream
fputc	output a character or word to a stream
fputs	output a line to a stream
fread	binary stream input/output
freopen	stream open functions
fscanf	input format conversion
fseek	reposition a stream
fsetpos	reposition a stream
ftell	reposition a stream
fwrite	binary stream input/output
getc	get next character or word from input stream
getchar	get next character or word from input stream
gets	get a line from a stream
getw	get next character or word from input stream
mktemp	make temporary filename (unique)
perror	system error messages
printf	formatted output conversion
putc	output a character or word to a stream
putchar	output a character or word to a stream
puts	output a line to a stream
putw	output a character or word to a stream
remove	remove directory entry
rewind	reposition a stream
scanf	input format conversion
setbuf	stream buffering operations
setbuffer	stream buffering operations
setlinebuf	stream buffering operations
setvbuf	stream buffering operations
sprintf	formatted output conversion
sscanf	input format conversion
strerror	system error messages
sys_errlist	system error messages
sys_nerr	system error messages
tempnam	temporary file routines
tmpfile	temporary file routines
tmpnam	temporary file routines
ungetc	un-get character from input stream
vfprintf	formatted output conversion
vfscanf	input format conversion
vprintf	formatted output conversion
vscanf	input format conversion
vsprintf	formatted output conversion
vsscanf	input format conversion
.TE
.SH CONFORMING TO
The
.I stdio
library conforms to C89.
.SH SEE ALSO
.BR close (2),
.BR open (2),
.BR read (2),
.BR write (2),
.BR stdout (3),
.BR unlocked_stdio (3)
.SH COLOPHON
This page is part of release 4.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.