STDIO(3) Linux Programmer's Manual 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 func-
tions 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. Cre-
ating 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 posi-
tion 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 reposi-
tioned 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 stan-
dard 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.
LISTOFFUNCTIONS
FunctionDescription
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
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
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
mktemp make temporary file name (unique)
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
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
vsprintf formatted output conversion
vsscanf input format conversion
CONFORMINGTO
The stdio library conforms to ANSI X3.159-1989 (''ANSI C'').
SEEALSO
open(2), close(2), read(2), write(2), stdout(3)
2001-12-26 STDIO(3)
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