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.\"     @(#)stdio.3	8.7 (Berkeley) 4/19/94
.\"
.Dd August 29, 2020
.Dt STDIO 3
.Os
.Sh NAME
.Nm stdio
.Nd standard input/output library functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Vt FILE *stdin;
.Vt FILE *stdout;
.Vt FILE *stderr;
.Sh DESCRIPTION
The standard
.Tn I/O
library provides a simple and efficient buffered stream
.Tn I/O
interface.
Input and output is mapped into logical data streams
and the physical
.Tn I/O
characteristics are concealed.
.Pp
A stream is associated with an external file (which may be a physical
device) by
.Em 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
.Em 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, the position indicator is placed at the end-of-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
.Xr fgetc 3
function; all output takes place as if all characters were
written by successive calls to the
.Xr fputc 3
function.
.Pp
A file is disassociated from a stream by
.Em 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
.Dv 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
.Xr 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
.Xr abort 3
do not bother about closing files properly.
.Pp
This implementation needs and makes
no distinction between
.Dq text
and
.Dq binary
streams.
In effect, all streams are binary.
No translation is performed and no extra padding appears on any stream.
.Pp
At program startup, three streams are predefined and need not be
opened explicitly:
.Bl -enum -offset indent
.It
.Em standard input
for reading conventional input,
.It
.Em standard output
for writing conventional output, and
.It
.Em standard error
for writing diagnostic output.
.El
.Pp
These streams are abbreviated
.Em stdin ,
.Em stdout ,
and
.Em stderr .
.Pp
Initially, the standard error stream
is unbuffered; the standard input and output streams are
fully buffered if and only if the streams do not refer to
an interactive or
.Dq terminal
device, as determined by the
.Xr isatty 3
function.
In fact,
.Em all
freshly-opened streams that refer to terminal devices
default to line buffering, and
pending output to such streams is written automatically
whenever such an input stream is read.
Note that this applies only to
.Dq "true reads" ;
if the read request can be satisfied by existing buffered data,
no automatic flush will occur.
In these cases,
or when a large amount of computation is done after printing
part of a line on an output terminal, it is necessary to
.Xr fflush 3
the standard output before going off and computing so that the output
will appear.
Alternatively, these defaults may be modified via the
.Xr setvbuf 3
function.
.Sh IMPLEMENTATION NOTES
In multi-threaded applications, operations on streams perform implicit
locking, except for the
.Fn getc_unlocked ,
.Fn getchar_unlocked ,
.Fn putc_unlocked ,
and
.Fn putchar_unlocked
functions.
Explicit control of stream locking is available through the
.Fn flockfile ,
.Fn ftrylockfile ,
and
.Fn funlockfile
functions .
.Pp
The following are defined as macros; these names may not be re-used
without first removing their current definitions with
.Dv #undef :
.Dv BUFSIZ ,
.Dv EOF ,
.Dv FILENAME_MAX ,
.Dv FOPEN_MAX ,
.Dv L_cuserid ,
.Dv L_ctermid ,
.Dv L_tmpnam ,
.Dv NULL ,
.Dv SEEK_END ,
.Dv SEEK_SET ,
.Dv SEE_CUR ,
.Dv TMP_MAX ,
.Fn clearerr ,
.Fn feof ,
.Fn ferror ,
.Fn fileno ,
.Fn freopen ,
.Fn fwopen ,
.Fn getc ,
.Fn getc_unlocked ,
.Fn getchar ,
.Fn getchar_unlocked ,
.Fn putc ,
.Fn putc_unlocked ,
.Fn putchar ,
.Fn putchar_unlocked ,
.Dv stderr ,
.Dv stdin ,
.Dv stdout .
.Pp
Function versions of the macro functions
.Fn feof ,
.Fn ferror ,
.Fn clearerr ,
.Fn fileno ,
.Fn getc ,
.Fn getc_unlocked ,
.Fn getchar ,
.Fn getchar_unlocked ,
.Fn putc ,
.Fn putc_unlocked ,
.Fn putchar ,
and
.Fn putchar_unlocked
exist and will be used if the macros definitions are explicitly removed.
.Sh SEE ALSO
.Xr close 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr write 2
.Sh STANDARDS
The
.Nm
library conforms to
.St -ansiC .
.Sh LIST OF FUNCTIONS
.Bl -column "putchar_unlocked" "Description"
.It Sy Function	Description
.It asprintf	formatted output conversion with allocation
.It asprintf_l	formatted output conversion with allocation
.It clearerr	check and reset stream status
.It dprintf	formatted output conversion
.It dprintf_l	formatted output conversion
.It fclose	close a stream
.It fdopen	stream open functions
.It feof	check and reset stream status
.It ferror	check and reset stream status
.It fflush	flush a stream
.It fgetc	get next character or word from input stream
.It fgetln	get a line from a stream
.It fgetpos	reposition a stream
.It fgets	get a line from a stream
.It fgetwc	get next wide character from input stream
.It fileno	check and reset stream status
.It flockfile	lock a stream
.It fmemopen	open a stream that points to a memory buffer
.It fopen	stream open functions
.It fprintf	formatted output conversion
.It fprintf_l	formatted output conversion
.It fpurge	flush a stream
.It fputc	output a character or word to a stream
.It fputs	output a line to a stream
.It fputwc	output a wide character to a stream
.It fread	binary stream input/output
.It freopen	stream open functions
.It fropen	open a stream
.It fscanf	input format conversion
.It fscanf_l	input format conversion
.It fseek	reposition a stream
.It fseeko	reposition a stream
.It fsetpos	reposition a stream
.It ftell	reposition a stream
.It ftello	reposition a stream
.It ftrylockfile	lock a stream (non-blocking)
.It funlockfile	unlock a stream
.It funopen	open a stream
.It funopen2	open a stream, with flush support
.It fwide	set/get orientation of a stream
.It fwopen	open a stream
.It fwrite	binary stream input/output
.It getc	get next character or word from input stream
.It getc_unlocked	get next character or word from input stream
.It             Ta (no implicit locking)
.It getchar	get next character or word from input stream
.It getchar_unlocked	get next character or word from input stream
.It             Ta (no implicit locking)
.It getdelim	get a delimited record from a stream
.It getline	get a line from a stream
.It gets	get a line from a stream
.It getw	get next character or word from input stream
.It getwc	get next wide character from input stream
.It getwchar	get next wide character from input stream
.It mkstemp	create unique temporary file
.It mktemp	create unique temporary file
.It open_memstream	open memory as a stream
.It popen	open a program as a stream
.It popenve	open a program as a stream
.It pclose	close an opened program stream
.It perror	system error messages
.It printf	formatted output conversion
.It printf_l	formatted output conversion
.It putc	output a character or word to a stream
.It putc_unlocked	output a character or word to a stream
.It             Ta (no implicit locking)
.It putchar	output a character or word to a stream
.It putchar_unlocked	output a character or word to a stream
.It             Ta (no implicit locking)
.It puts	output a line to a stream
.It putw	output a character or word to a stream
.It putwc	output a wide character to a stream
.It putwchar	output a wide character to a stream
.It remove	remove directory entry
.It rewind	reposition a stream
.It scanf	input format conversion
.It scanf_l	input format conversion
.It setbuf	stream buffering operations
.It setbuffer	stream buffering operations
.It setlinebuf	stream buffering operations
.It setvbuf	stream buffering operations
.It snprintf	formatted output conversion
.It snprintf_l	formatted output conversion
.It sprintf	formatted output conversion
.It sscanf	input format conversion
.It sscanf_l	input format conversion
.It strerror	system error messages
.It sys_errlist	system error messages
.It sys_nerr	system error messages
.It tempnam	temporary file routines
.It tmpfile	temporary file routines
.It tmpnam	temporary file routines
.It ungetc	un-get character from input stream
.It ungetwc	un-get wide character from input stream
.It vasprintf	formatted output conversion with allocation
.It vasprintf_l	formatted output conversion with allocation
.It vdprintf	formatted output conversion
.It vdprintf_l	formatted output conversion
.It vfprintf	formatted output conversion
.It vfprintf_l	formatted output conversion
.It vfscanf	input format conversion
.It vfscanf_l	input format conversion
.It vprintf	formatted output conversion
.It vprintf_l	formatted output conversion
.It vscanf	input format conversion
.It vscanf_l	input format conversion
.It vsnprintf	formatted output conversion
.It vsnprintf_l	formatted output conversion
.It vsprintf	formatted output conversion
.It vsprintf_l	formatted output conversion
.It vsscanf	input format conversion
.It vsscanf_l	input format conversion
.El
.Sh BUGS
The standard buffered functions do not interact well with certain other
library and system functions, especially
.Xr vfork 2
and
.Xr abort 3 .