1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <config.h>
include <syserr.h>
include <fio.h>
# SEEK -- Position the i/o pointer (file offset at which the next i/o transfer
# will occur) for a file. Note that ITOP may have to be adjusted before
# performing the seek, to make newly written data readable (as when writing at
# EOF, seeking backward within the same buffer, and reading). A physical seek
# is performed for text files. For binary files, a logical seek is performed,
# adjusting the i/o pointer. Physical seeks on binary files are initiated
# by FFAULT, when filling or flushing a file buffer.
procedure seek (fd, offset)
int fd # file
long offset # offset == BOF,EOF, or char offset
pointer bp
long file_offset
int status
long ffilsz()
errchk filerr, syserr, ffilsz
include <fio.com>
begin
fp = fiodes[fd]
if (fd <= 0 || fp == NULL)
call syserr (SYS_FILENOTOPEN)
call fcanpb (fd) # cancel any pushback
UPDATE_IOP(fd) # make newly written data readable
if (FTYPE(fp) == TEXT_FILE) {
# General seeks only permitted on text files opened for reading.
if (FMODE(fp) != READ_ONLY)
if (offset != BOF && offset != EOF)
call filerr (FNAME(fp), SYS_FSEEKNTXF)
bp = bufptr[fd]
if (BUF_MODIFIED(fd)) { # flush buffer?
call fputtx (fd, Memc[bp], otop[fd] - bp, status)
if (status != ERR)
call zcall2 (ZFLSTX(fp), FCHAN(fp), status)
if (status == ERR)
call filerr (FNAME(fp), SYS_FWRITE)
}
iop[fd] = bp
itop[fd] = bp
otop[fd] = bp
call zcall3 (ZSEKTX(fp), FCHAN(fp), offset, status)
if (status == ERR)
call filerr (FNAME(fp), SYS_FSEEK)
} else { # logical seek (binary files)
switch (offset) {
case BOF:
file_offset = 1
case EOF:
file_offset = ffilsz (fd) + 1
default:
file_offset = offset
}
iop[fd] = file_offset - boffset[fd] + bufptr[fd]
}
end
|
