STDIO(3)                                            Linux 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 device) by opening a file, which may involve creat-
       ing 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,  it
       is unspecified whether the position indicator will be placed at the start or the end of the 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 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.

       At  program  startup,  three text streams are predefined and need not be opened explicitly -- standard input (for reading
       conventional input), -- standard output (for writing conventional input), and standard error (for writing diagnostic out-
       put).   These  streams  are  abbreviated  stdin,stdout  and  stderr.  When opened, the standard error stream is not fully
       buffered; the standard input and output streams are fully buffered if and only if the streams  do  not  to  refer  to  an
       interactive device.

       Output  streams  that  refer  to  terminal devices are always line buffered by default; pending output to such streams is
       written automatically whenever an input stream that refers to a terminal device is read.  In cases where 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.

       The stdio library is a part of the library libc and routines are automatically loaded as needed by  the  compilers  cc(1)
       and  pc(1).   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 reused 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, 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 macros
       definitions are explicitly removed.

   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
       fgetpos       reposition a stream
       fgets         get a line from a stream
       fileno        return the integer descriptor of the argument 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
       fread         binary stream input/output
       freopen       stream open functions
       fscanf        input format conversion
       fseek         reposition a stream
       fsetpos       reposition a stream
       ftell         reposition 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
       mktemp        make temporary filename (unique)
       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
       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
       vsprintf      formatted output conversion
       vsscanf       input format conversion

CONFORMING TO
       The stdio library conforms to C89.

SEE ALSO
       close(2), open(2), read(2), write(2), stdout(3), unlocked_stdio(3)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                                           2001-12-26                                                   STDIO(3)