setbuffer, setlinebuf - assign buffering to a stream


     #include <stdio.h>

     void setbuffer(FILE *iop, char *abuf, size_t asize);

     int setlinebuf(FILE *iop);


     The setbuffer() and setlinebuf() functions assign  buffering
     to  a  stream.  The  three  types of buffering available are
     unbuffered, block buffered, and line buffered.  When an out-
     put  stream is unbuffered, information appears on the desti-
     nation file or terminal as soon as written; when it is block
     buffered,  many characters are saved and written as a block;
     when it is line buffered, characters are saved until  either
     a  NEWLINE  is  encountered or input is read from stdin. The
     fflush(3C) function may be  used  to  force  the  block  out
     early.  Normally  all  files are block buffered. A buffer is
     obtained from malloc(3C) upon the first getc(3C) or putc(3C)
     performed  on the file. If the standard stream stdout refers
     to a terminal, it is  line  buffered.  The  standard  stream
     stderr is unbuffered by default.

     The setbuffer() function can be used after a stream iop  has
     been  opened  but  before it is read or written. It uses the
     character array abuf whose size is determined by  the  asize
     argument  instead  of an automatically allocated buffer.  If
     abuf is the null pointer, input/output  will  be  completely
     unbuffered.   A  manifest  constant  BUFSIZ,  defined in the
     <stdio.h> header, tells how large an array is needed:

          char buf[BUFSIZ];

     The setlinebuf() function is used to change the buffering on
     a stream from block buffered or unbuffered to line buffered.
     Unlike setbuffer(), it can be used  at  any  time  that  the
     stream iop is active.

     A stream can be changed from unbuffered or line buffered  to
     block buffered by using freopen(3C). A stream can be changed
     from block buffered or line buffered to unbuffered by  using
     freopen(3C) followed by setbuf(3C) with a buffer argument of


     The setlinebuf() function returns no useful value.


     malloc(3C),  fclose(3C),  fopen(3C),  fread(3C),   getc(3C),
     printf(3C), putc(3C), puts(3C), setbuf(3C), setvbuf(3C)


     A common source of error is allocating buffer  space  as  an
     "automatic"  variable  in  a code block, and then failing to
     close the stream in the same block.

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