STDIO(3)                  OpenBSD 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 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 de-
     vice) 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 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.
     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 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 with-
     out 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, 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 macro defini-
     tions are explicitly removed.

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

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

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
     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
     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
     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

OpenBSD 2.6                     April 19, 1994                               3