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Manual Pages  — STDIO

NAME

stdio – standard input/output library functions

CONTENTS

LIBRARY

Standard C Library (libc, -lc)

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 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 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 (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 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:

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 C 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_ctermid, L_cuserid, L_tmpnam, NULL, P_tmpdir, SEEK_CUR, SEEK_END, SEEK_SET, TMP_MAX, clearerr, clearerr_unlocked, feof, feof_unlocked, ferror, ferror_unlocked, fileno, fileno_unlocked, fropen, fwopen, getc, getc_unlocked, getchar, getchar_unlocked, putc, putc_unlocked, putchar, putchar_unlocked, stderr, stdin and stdout. Function versions of the macro functions clearerr, clearerr_unlocked, feof, feof_unlocked, ferror, ferror_unlocked, fileno, fileno_unlocked, getc, getc_unlocked, getchar, getchar_unlocked, putc, putc_unlocked, putchar, and putchar_unlocked exist and will be used if the macro definitions are explicitly removed.

SEE ALSO

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

STANDARDS

The stdio library conforms to ISO/IEC 9899:1999 ("ISO C99").

LIST OF FUNCTIONS

Function Description

asprintf
formatted output conversion

clearerr
check and reset stream status

dprintf
formatted output conversion

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

fgetwc
get next wide character from input stream

fgetws
get a line of wide characters 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

fputwc
output a wide character to a stream

fputws
output a line of wide characters 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

fwide
set/get orientation of stream

fwopen
open a stream

fwprintf
formatted wide character output conversion

fwrite
binary stream input/output

getc
get next character or word from input stream

getchar
get next character or word from input stream

getdelim
get a line from a stream

getline
get a line from a stream

gets
get a line from a stream

getw
get next character or word from input stream

getwc
get next wide character from input stream

getwchar
get next wide character from input stream

mkdtemp
create unique temporary directory

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

putwc
output a wide character to a stream

putwchar
output a wide character 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

swprintf
formatted wide character output conversion

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

ungetwc
un-get wide character from input stream

vasprintf
formatted output conversion

vdprintf
formatted output conversion

vfprintf
formatted output conversion

vfscanf
input format conversion

vfwprintf
formatted wide character output conversion

vprintf
formatted output conversion

vscanf
input format conversion

vsnprintf
formatted output conversion

vsprintf
formatted output conversion

vsscanf
input format conversion

vswprintf
formatted wide character output conversion

vwprintf
formatted wide character output conversion

wprintf
formatted wide character output conversion

BUGS

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

STDIO (3) March 3, 2009

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