stdio - standard input/output library functions
#include <stdio.h>
FILE *stdin;
FILE *stdout;
FILE *stderr;
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.
A stream is associated with an external file (which may be a
physical device)
by ``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 ``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
fgetc(3) function;
all output takes place as if all characters were written by successive
calls to the fputc(3) function.
A file is disassociated from a stream by ``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 FILE object is indeterminate (garbage) after a file is
closed.
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 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, _exit(2) does not flush
stdio files.
Neither does an exit due to a signal. Buffers are flushed
by abort(3) as
required by POSIX, although previous implementations did
not.
This implementation needs and makes no distinction between
``text'' and
``binary'' streams. In effect, all streams are binary. No
translation
is performed and no extra padding appears on any stream.
At program startup, three streams are predefined and need
not be opened
explicitly:
+o standard input (for reading conventional input),
+o standard output (for writing conventional output),
and
+o standard error (for writing diagnostic output).
These streams are abbreviated stdin, stdout, and 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 ``terminal'' device, as determined by the
isatty(3) function.
In fact, 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 ``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 fflush(3) the
standard output
before going off and computing so that the output will appear. Alternatively,
these defaults may be modified via the setvbuf(3)
function.
The stdio library is a part of the library libc and routines
are automatically
loaded as needed by the compiler. 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.
The following are defined as macros; these names may not be
re-used without
first removing their current definitions with #undef:
BUFSIZ, EOF,
FILENAME_MAX, FOPEN_MAX, L_cuserid, L_ctermid, L_tmpnam,
NULL, SEEK_END,
SEEK_SET, SEE_CUR, TMP_MAX, clearerr, feof, ferror, fileno,
freopen,
fwopen, getc, getchar, putc, putchar, stderr, stdin, stdout.
Function
versions of the macro functions feof, ferror, clearerr,
fileno, getc,
getchar, putc, and putchar exist and will be used if the
macro definitions
are explicitly removed.
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
close(2), open(2), read(2), write(2)
The stdio library conforms to ANSI X3.159-1989 (``ANSI C'').
The standard buffered functions do not interact well with
certain other
library and system functions, especially vfork and abort.
OpenBSD 3.6 April 19, 1994
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