projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 7bd0b8c0 | 1 | /* |
| 161423a6 RE |
2 | * Copyright (c) 1980 Regents of the University of California. |
| 3 | * All rights reserved. The Berkeley software License Agreement | |
| 4 | * specifies the terms and conditions for redistribution. | |
| 7bd0b8c0 | 5 | * |
| afe045b5 | 6 | * @(#)backspace.c 5.2 %G% |
| 161423a6 RE |
7 | */ |
| 8 | ||
| 9 | /* | |
| 7bd0b8c0 DW |
10 | * Backspace records |
| 11 | */ | |
| 12 | ||
| 13 | #include "fio.h" | |
| 14 | ||
| fdfc35cb DW |
15 | static char bksp[] = "backspace"; |
| 16 | char last_char(); | |
| 7bd0b8c0 | 17 | |
| fdfc35cb DW |
18 | f_back(a) |
| 19 | alist *a; | |
| 7bd0b8c0 DW |
20 | { unit *b; |
| 21 | int n,i; | |
| 22 | long x,y; | |
| 2621bc46 | 23 | |
| 7bd0b8c0 DW |
24 | lfname = NULL; |
| 25 | elist = NO; | |
| 26 | external = YES; | |
| 27 | errflag = a->aerr; | |
| 28 | lunit = a->aunit; | |
| fdfc35cb DW |
29 | if (not_legal(lunit)) |
| 30 | err(errflag, F_ERUNIT, bksp) | |
| 7bd0b8c0 | 31 | b= &units[lunit]; |
| afe045b5 | 32 | if(!b->ufd) return(OK); |
| 7bd0b8c0 DW |
33 | lfname = b->ufnm; |
| 34 | if(b->uend) | |
| 35 | { b->uend = NO; | |
| 1604dff5 | 36 | clearerr(b->ufd); |
| 7bd0b8c0 DW |
37 | return(OK); |
| 38 | } | |
| fdfc35cb DW |
39 | if((x = ftell(b->ufd)) == 0) |
| 40 | return(OK); | |
| 41 | if(!b->useek) | |
| 42 | err(errflag, F_ERNOBKSP, bksp) | |
| 331ef099 | 43 | if(b->uwrt && (n = t_runc(b, errflag, bksp))) /* sets 'reading' */ |
| fdfc35cb | 44 | return(n); |
| 7bd0b8c0 DW |
45 | if(b->url) /* direct access, purely academic */ |
| 46 | { y = x%(long)b->url; | |
| 47 | x -= y?y:b->url; | |
| 48 | fseek(b->ufd,x,0); | |
| 49 | return(OK); | |
| 50 | } | |
| 51 | if(!b->ufmt) /* unformatted sequential */ | |
| 52 | { fseek(b->ufd,-(long)sizeof(int),1); | |
| 53 | fread((char *)&n,sizeof(int),1,b->ufd); | |
| 54 | fseek(b->ufd,-(long)n-2*sizeof(int),1); | |
| 55 | return(OK); | |
| 56 | } | |
| fdfc35cb | 57 | if(x == 1) /* formatted sequential */ |
| 7bd0b8c0 DW |
58 | { rewind(b->ufd); |
| 59 | return(OK); | |
| 60 | } | |
| fdfc35cb DW |
61 | while (last_char(b->ufd) != '\n') /* slow but simple */ |
| 62 | ; | |
| 7bd0b8c0 DW |
63 | return(OK); |
| 64 | } |