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 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 read by
successive calls to the
fputc (3)
function.
A file is disassociated from a stream by
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
FILE
object is indeterminate after a file is closed (garbage).
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,
such as
abort (3)
do not bother about closing files properly.
At program startup, three text streams are predefined and need not be
opened explicitly
standard input
(for reading conventional input),
standard output
(for writing conventional input), and
standard error
(for writing diagnostic output). These streams are abbreviated
stdin , stdout
and
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 to refer to an interactive device.
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
fflush (3)
the standard output before going off and computing so that the output will
appear.
The
stdio
library is a part of the library
libc
and routines are automatically loaded as needed by the compilers
cc (1)
and
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.
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 ,
fropen ,
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 macros definitions are explicitly removed.
