path: root/lib/libc/stdio/stdio.3

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.Dd April 19, 1994
.Dt STDIO 3
.Os
.Sh NAME
.Nm stdio
.Nd standard input/output library functions
.Sh SYNOPSIS
.Fd #include <stdio.h>
.Pp
.Fd FILE *stdin;
.Fd FILE *stdout;
.Fd 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.
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
.Dq 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
.Dq 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 will be 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
.Dq closing
it.
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 (garbage) after a file is closed.
.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 may not close files properly and hence
buffered output may be lost.
In particular,
.Xr _exit 2
does not flush stdio files.
Neither does an exit due to a signal.
Buffers are flushed by
.Xr abort 3
as required by POSIX, although previous implementations did not.
.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:
.Pp
.Bl -bullet -compact -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 .
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.
.Pp
The
.Nm stdio
library is a part of the library
.Xr libc
and routines are automatically loaded as needed by the compiler.
The
.Tn 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 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 ,
.Dv clearerr ,
.Dv feof ,
.Dv ferror ,
.Dv fileno ,
.Dv freopen ,
.Dv fwopen ,
.Dv getc ,
.Dv getchar ,
.Dv putc ,
.Dv putchar ,
.Dv stderr ,
.Dv stdin ,
.Dv stdout .
Function versions of the macro functions
.Xr feof ,
.Xr ferror ,
.Xr clearerr ,
.Xr fileno ,
.Xr getc ,
.Xr getchar ,
.Xr putc ,
and
.Xr putchar
exist and will be used if the macro
definitions are explicitly removed.
.Sh LIST OF FUNCTIONS
.Bl -column "Description"
.Sy Function	Description
asprintf	formatted output conversion with allocation
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
fgetln	get a line from a stream
fgetpos	reposition a stream
fgets	get a line from a stream
fileno	get a stream's underlying file descriptor
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
fropen	open a stream
fscanf	input format conversion
fseek	reposition a stream
fsetpos	reposition a stream
ftell	reposition a stream
funopen	open a stream
fwopen	open 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
mkstemp	create unique temporary file
mktemp	create unique temporary file
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
snprintf	formatted output conversion
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
vasprintf	formatted output conversion with allocation
vfprintf	formatted output conversion
vfscanf	input format conversion
vprintf	formatted output conversion
vscanf	input format conversion
vsnprintf	formatted output conversion
vsprintf	formatted output conversion
vsscanf	input format conversion
.El
.Sh SEE ALSO
.Xr close 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr write 2
.Sh STANDARDS
The
.Nm stdio
library conforms to
.St -ansiC .
.Sh BUGS
The standard buffered functions do not interact well with certain other
library and system functions, especially
.Xr vfork
and
.Xr abort .