* Copyright (c) 1990 The Regents of the University of California.
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley. The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
// Modified for GNU iostream by Per Bothner 1991.
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "%W% (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */
* Allocate a file buffer, or switch to unbuffered I/O.
* Per the ANSI C standard, ALL tty devices default to line buffered.
* As a side effect, we set __SOPT or __SNPT (en/dis-able fseek
* optimisation) right after the _fstat() that finds the buffer size.
int filebuf::doallocate()
register size_t size, couldbetty;
if (fd() < 0 || _fstat(fd(), &st) < 0) {
/* do not try to optimise fseek() */
couldbetty = S_ISCHR(st.st_mode);
size = st.st_blksize <= 0 ? _G_BUFSIZ : st.st_blksize;
if ((p = malloc(size)) == NULL) {
// fp->_bf._base = fp->_p = fp->_nbuf;
if (couldbetty && _isatty(fd()))