STDIO(3) BSD Programmer's Manual STDIO(3)
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 in-
dicator will be placed at the end-of-file. The position indicator is
maintained by subsequent reads, writes, and positioning requests. All in-
put occurs as if the characters were read by successive calls to the
fgetc(3) function; all output takes place as if all characters were writ-
ten 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 en-
vironment) 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 exe-
cution, 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 out-
put streams are flushed) before program termination. Other methods of
program termination may not close files properly and hence buffered out-
put may be lost. In particular, _exit(2) does not flush stdio files. Nei-
ther does an exit due to a signal. Buffers are flushed by abort(3) as re-
quired 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:
• 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) func-
tion. 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 ap-
plies only to "true reads"; if the read request can be satisfied by ex-
isting 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. Alterna-
tively, these defaults may be modified via the setvbuf(3) function.
The stdio library is a part of the library libc and routines are automat-
ically 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, SEEK_CUR, TMP_MAX, clearerr, feof, ferror, fileno,
freopen, fwopen, getc, getchar, putc, putchar, stderr, stdin, stdout.
Function versions of the macro functions feof(3), ferror(3), clearerr(3),
fileno(3), getc(3), getchar(3), putc(3), and putchar(3) 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 C89").
The standard buffered functions do not interact well with certain other
library and system functions, especially vfork(2) and abort(3).
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