STDIO(3) Library Functions Manual STDIO(3)
NAME
stdiostandard input/output library functions
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.
 
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 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:
1.
standard input for reading conventional input,
2.
standard output for writing conventional output, and
3.
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.
IMPLEMENTATION NOTES
In multi-threaded applications, operations on streams perform implicit locking, except for the getc_unlocked(), getchar_unlocked(), putc_unlocked(), and putchar_unlocked() functions. Explicit control of stream locking is available through the flockfile(), ftrylockfile(), and funlockfile() functions .
 
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(), getc_unlocked(), getchar(), getchar_unlocked(), putc(), putc_unlocked(), putchar(), putchar_unlocked(), stderr, stdin, stdout.
 
Function versions of the macro functions feof(), ferror(), clearerr(), fileno(), getc(), getc_unlocked(), getchar(), getchar_unlocked(), putc(), putc_unlocked(), putchar(), and putchar_unlocked() exist and will be used if the macros definitions are explicitly removed.
SEE ALSO
STANDARDS
The stdio library conforms to ANSI X3.159-1989 (“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
fgetwc
get next wide character from input stream
fileno
check and reset stream status
flockfile
lock a stream
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
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
ftrylockfile
lock a stream (non-blocking)
funlockfile
unlock a stream
funopen
open a stream
fwide
set/get orientation of a stream
fwopen
open a stream
fwrite
binary stream input/output
getc
get next character or word from input stream
getc_unlocked
get next character or word from input stream
(no implicit locking)
getchar
get next character or word from input stream
getchar_unlocked
get next character or word from input stream
(no implicit locking)
getdelim
get a delimited record 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
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
putc_unlocked
output a character or word to a stream
(no implicit locking)
putchar
output a character or word to a stream
putchar_unlocked
output a character or word to a stream
(no implicit locking)
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
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
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
BUGS
The standard buffered functions do not interact well with certain other library and system functions, especially vfork(2) and abort(3).