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STDIO(3V)                                                            STDIO(3V)

       stdio - standard buffered input/output package

       #include <&lt;stdio.h>&gt;

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

       The  functions  described  in  section  3S  constitute a user-level I/O
       buffering scheme.  The in-line  macros  getc(3V)  and  putc(3S)  handle
       characters  quickly.  The macros getchar() (see getc(3V)) and putchar()
       (see putc(3S)), and the higher  level  routines  fgetc(),  getw()  (see
       getc(3V)),  gets(3S),  fgets() (see gets(3S)), scanf(3V), fscanf() (see
       scanf(3V)),  fread(3S),  fputc(),  putw()  (see  putc(3S)),   puts(3S),
       fputs()   (see   puts(3S)),  printf(3V),  fprintf()  (see  printf(3V)),
       fwrite() (see fread(3S)) all use or act  as  if  they  use  getc()  and
       putc().  They can be freely intermixed.

       A file with associated buffering is called a stream, and is declared to
       be a pointer  to  a  defined  type  FILE.   fopen(3V)  creates  certain
       descriptive  data  for  a stream and returns a pointer to designate the
       stream in all further transactions.  Normally,  there  are  three  open
       streams  with  constant pointers declared in the <&lt;stdio.h>&gt; include file
       and associated with the standard open files:

       stdin     standard input file
       stdout    standard output file
       stderr    standard error file

       A constant NULL (0) designates a nonexistent pointer.

       An integer constant EOF (-1) is returned upon  EOF  or  error  by  most
       integer  functions  that deal with streams (see the individual descrip-
       tions for details).

       Any module that uses this package must include the header file of  per-
       tinent macro definitions, as follows:

              #include <&lt;stdio.h>&gt;

       The  functions  and  constants mentioned in sections labeled 3S of this
       manual are declared in that header file and need  no  further  declara-
       tion.   The  constants and the following `functions' are implemented as
       macros; redeclaration of these names is  perilous:  getc(),  getchar(),
       putc(), putchar(), feof(), ferror(), fileno(), and clearerr().

       Output streams, with the exception of the standard error stream stderr,
       are by default buffered if the  output  refers  to  a  file  and  line-
       buffered if the output refers to a terminal.  The standard error output
       stream stderr is by default unbuffered, but use of fopen()  will  cause
       it  to  become  buffered  or  line-buffered.   When an output stream is
       unbuffered, information is written to the destination file or  terminal
       as  soon as it is output to the stream; when it is buffered, many char-
       acters are saved up and written as a block.  When it is  line-buffered,
       each  line  of output is written to the destination file or terminal as
       soon as the line is completed (that is, as soon as a NEWLINE  character
       is  output  or,  if  the  output stream is stdout or stderr, as soon as
       input is read from stdin).  setbuf(3V), setbuffer(),  setlinebuf(),  or
       setvbuf() (see setbuf(3V)) can be used to change the stream's buffering

       When an output stream is line-buffered, each line of output is  written
       to  the  destination  file or terminal as soon as the line is completed
       (that is, as soon as a NEWLINE character is output or as soon as  input
       is read from a line-buffered stream).

       Output  saved  up on all line-buffered streams is written when input is
       read from any line-buffered stream.  Input read from a stream  that  is
       not line-buffered does not flush output on line-buffered streams.

       The value EOF is returned uniformly to indicate that a FILE pointer has
       not been initialized with fopen(), input (output) has been attempted on
       an  output (input) stream, or a FILE pointer designates corrupt or oth-
       erwise unintelligible FILE data.

       open(2V), close(2V), lseek(2V), pipe(2V),  read(2V),  write(2V),  cter-
       mid(3V),  cuserid(3V),  fclose(3V),  ferror(3V),  fopen(3V), fread(3S),
       fseek(3S),  getc(3V),  gets(3S),   popen(3S),   printf(3V),   putc(3S),
       puts(3S),  scanf(3V),  setbuf(3V),  system(3), tmpfile(3S), tmpnam(3S),

       The line buffering of output to terminals is almost always transparent,
       but  may  cause confusion or malfunctioning of programs which use stan-
       dard I/O routines but use read(2V) to read from the standard input,  as
       calls  to  read()  do  not  cause output to line-buffered streams to be

       In cases where a large amount of computation  is  done  after  printing
       part  of a line on an output terminal, it is necessary to call fflush()
       (see fclose(3V)) on the standard output before performing the  computa-
       tion so that the output will appear.

       The standard buffered functions do not interact well with certain other
       library and system functions, especially vfork(2).

                                21 January 1990                      STDIO(3V)