minix/lib/libc/stdio/stdio.3

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.\" $NetBSD: stdio.3,v 1.24 2010/05/05 04:13:16 jruoho Exp $
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.\" @(#)stdio.3 8.7 (Berkeley) 4/19/94
.\"
.Dd May 5, 2010
.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 will be placed 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
read 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 an 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 clearerr check and reset stream status
.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 fopen stream open functions
.It fprintf 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 fseek reposition a stream
.It fsetpos reposition a stream
.It ftell reposition a stream
.It ftrylockfile lock a stream (non-blocking)
.It funlockfile unlock a stream
.It funopen open a stream
.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 perror system error messages
.It printf 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 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 sprintf formatted output conversion
.It sscanf 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 vfprintf formatted output conversion
.It vfscanf input format conversion
.It vprintf formatted output conversion
.It vscanf input format conversion
.It vsnprintf formatted output conversion
.It vsprintf formatted output conversion
.It vsscanf 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 .