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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <config.h>
include <syserr.h>
include <fio.h>
# UNGETLINE -- Push an EOS delimited string back into the input stream.
# The next getc will return the first char of the pushed back string,
# followed by successive chars in the string until EOS is reached, at which
# time input reverts to wherever it was before pushback. Pushback is last
# in first out, i.e., the last string pushed will be the first string scanned
# when reading. Multiple characters and strings may be pushed back into the
# input until the push back buffer overflows. Overflow is often an indication
# of recursion in whatever routine is doing the pushback.
#
# N.B.: this routine really pushes a string, not a line, i.e. we don't give
# a whiz about newline characters.
procedure ungetline (fd, str)
int fd # file
char str[ARB] # string to be pushed back
int or()
pointer ip, pb_iop, pb_sp, iop_limit
errchk syserr, syserrs, fmkpbbuf
include <fio.com>
begin
fp = fiodes[fd]
if (fd <= 0 || fp == NULL)
call syserr (SYS_FILENOTOPEN)
if (str[1] == EOS)
return
if (FPBBUF(fp) == NULL)
call fmkpbbuf (fd)
# Push the old pb_iop, iop, itop and bufptr on the stack for later
# restoration of the interrupted input stream by filbuf. Note bufptr
# must be changed to point to a value less than iop to avoid a buffer
# fault.
pb_sp = FPBSP(fp) - 1
pb_iop = FPBIOP(fp)
Memi[pb_sp] = pb_iop
pb_sp = pb_sp - 1
Memi[pb_sp] = bufptr[fd]
pb_sp = pb_sp - 1
Memi[pb_sp] = itop[fd]
pb_sp = pb_sp - 1
Memi[pb_sp] = iop[fd]
# Copy the string into the buffer; abort if the buffer overflows.
# Set iop to point to first char of string. Note: pushed back chars
# grow upward while the stacked i/o pointers grow downward.
bufptr[fd] = pb_iop
iop[fd] = pb_iop
iop_limit = (pb_sp - 1) * SZ_INT + 1
for (ip=1; str[ip] != EOS; ip=ip+1) {
if (pb_iop >= iop_limit)
call syserrs (SYS_FPBOVFL, FNAME(fp))
Memc[pb_iop] = str[ip]
pb_iop = pb_iop + 1
}
itop[fd] = pb_iop
FPBSP(fp) = pb_sp
FPBIOP(fp) = pb_iop
fflags[fd] = or (fflags[fd], FF_PUSHBACK)
end
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