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NAME    [Toc]    [Back]

     stdio - standard input/output library functions

SYNOPSIS    [Toc]    [Back]

     #include <stdio.h>

     FILE *stdin;
     FILE *stdout;
     FILE *stderr;

DESCRIPTION    [Toc]    [Back]

     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

     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'' it.
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

     A  file may be subsequently reopened, by the same or another
program execution,
 and its contents reclaimed or modified (if it can be
     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

     This implementation needs and makes no  distinction  between
``text'' and
     ``binary''  streams.  In effect, all streams are binary.  No
     is performed and no extra padding appears on any stream.

     At program startup, three streams are  predefined  and  need
not be opened

           +o   standard input (for reading conventional input),
           +o   standard output (for writing conventional output),
           +o   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
     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)

     The stdio library is a part of the library libc and routines
are automatically
 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:
     FILENAME_MAX,  FOPEN_MAX,  L_cuserid,  L_ctermid,  L_tmpnam,
     SEEK_SET, SEE_CUR, TMP_MAX, clearerr, feof, ferror,  fileno,
     fwopen, getc, getchar, putc, putchar, stderr, stdin, stdout.
     versions of the  macro  functions  feof,  ferror,  clearerr,
fileno, getc,
     getchar,  putc,  and  putchar  exist and will be used if the
macro definitions
 are explicitly removed.

LIST OF FUNCTIONS    [Toc]    [Back]

     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

SEE ALSO    [Toc]    [Back]

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

STANDARDS    [Toc]    [Back]

     The stdio library conforms to ANSI X3.159-1989 (``ANSI C'').

BUGS    [Toc]    [Back]

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

OpenBSD     3.6                          April      19,      1994
[ Back ]
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