setvbuf

 NAME
  setvbuf - change file pointer's buffering

 SYNOPSIS
  #include <stdio.h>

  int error = setvbuf(fp, buf, mode, size);
  FILE *fp;
  char *buf;
  int mode;
  size_t size;

 FUNCTION
  setvbuf() changes the internal buffer used by stdio.  You may specify
  a new buffer of any size, change the buffering mode of the file
  pointer to fully buffered, line buffered, or unbuffered.

  mode:
      _IOFBF  fully buffered (output flushed only if buffer full)
      _IOLBF  line buffered (output flushed every newline)
      _IONBF  unbuffered (no buffering at all)

  For _IOFBF and _IOLBF, buf should point to the buffer you wish the
  file pointer to use and size should be the size of that buffer (any
  size other than 0 is valid).

  For_IONBF the buf and size arguments should be passed as NULL

 NOTE
                  !!

  If buffering is turned off for a file pointer representing a
  console device, the console device is set to unbuffered as well.

  If buffering is turned on for a file pointer representing a
  console device, the console device is set to buffered as well.

 EXAMPLE
  #include <stdio.h>

  main()
  {
      int c;
      static char iobuf[128];
      char buf[256];

      setvbuf(stdin, NULL, _IONBF, 0);

      printf("Type a character: ");
      fflush(stdout);
      c = getchar();
      printf("c = %dn", c);

      setvbuf(stdin, iobuf, _IOLBF, sizeof(iobuf));

      printf("Type a line: ");
      fflush(stdout);
      gets(buf);
      printf("You said: %sn", buf);

      return(0);
  }

 INPUTS
  FILE *fp;       file pointer to change buffering options on
  char *buf;      new buffer or NULL (_IONBF)
  int mode;       buffering mode
  size_t size;    size of new buffer if not NULL, else 0

 RESULTS
  int error;      0 on success, a negative number on error
                  (such as illegal arguments)

 SEE ALSO
  setbuf