STDIO(3)

NAME
stdio - standard input/output library functions

SYNOPSIS
#include <stdio.h>
FILE *stdin;
FILE *stdout;
FILE *stderr;

DESCRIPTION
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.

This implementation makes a distinction between text and binary streams. For text streams, all carrige returns are mapped to linefeeds during input, and all linefeeds are mapped to carrige returns on output. No extra padding appears on any stream.

At program startup, three streams are predefined and need not be opened explicitly:
    standard input (for reading conventional input),
    standard output (for writing conventional output), and
    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 an 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 linker. 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 macros definitions are explicitly removed.

SEE ALSO
open(2), close(2), read(2), write(2)

BUGS
The standard buffered functions do not interact well with certain other library and system functions, especially fork(2), fork2(2), vfork(2), and abort(3).

STANDARDS
The stdio library conforms to ANSI/C.

LIST OF FUNCTIONS
Function	Description
--------	-----------
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	check and reset stream status
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
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