4.3BSD - /usr/src/usr.lib/libI77/backspace.c

   1: /*
   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.
   5:  *
   6:  *	@(#)backspace.c	5.2	7/30/85
   7:  */
   8: 
   9: /*
  10:  * Backspace records
  11:  */
  12: 
  13: #include "fio.h"
  14: 
  15: static char bksp[]  = "backspace";
  16: char    last_char();
  17: 
  18: f_back(a)
  19: alist   *a;
  20: {   unit *b;
  21:     int n,i;
  22:     long x,y;
  23: 
  24:     lfname = NULL;
  25:     elist = NO;
  26:     external = YES;
  27:     errflag = a->aerr;
  28:     lunit = a->aunit;
  29:     if (not_legal(lunit))
  30:         err(errflag, F_ERUNIT, bksp)
  31:     b= &units[lunit];
  32:     if(!b->ufd) return(OK);
  33:     lfname = b->ufnm;
  34:     if(b->uend)
  35:     {   b->uend = NO;
  36:         clearerr(b->ufd);
  37:         return(OK);
  38:     }
  39:     if((x = ftell(b->ufd)) == 0)
  40:         return(OK);
  41:     if(!b->useek)
  42:         err(errflag, F_ERNOBKSP, bksp)
  43:     if(b->uwrt && (n = t_runc(b, errflag, bksp)))   /* sets 'reading' */
  44:         return(n);
  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:     }
  57:     if(x == 1)          /* formatted sequential */
  58:     {   rewind(b->ufd);
  59:         return(OK);
  60:     }
  61:     while (last_char(b->ufd) != '\n')   /* slow but simple */
  62:         ;
  63:     return(OK);
  64: }

Defined functions

Defined variables