BSD 4_1c_2 release

[unix-history] / usr / src / usr.lib / libI77 / backspace.c

/*
char id_backspace[] = "@(#)backspace.c  1.2";
*
* Backspace records
*/

#include "fio.h"

char *bksp = "backspace";
char last_char();

f_back(a) alist *a;
{       unit *b;
       int n,i;
       long x,y;
       lfname = NULL;
       elist = NO;
       external = YES;
       errflag = a->aerr;
       lunit = a->aunit;
       if (not_legal(lunit)) err(errflag,F_ERUNIT,bksp)
       b= &units[lunit];
       if(!b->ufd && (n=fk_open(READ,SEQ,FMT,(ftnint)lunit)) )
               err(errflag,n,bksp)
       lfname = b->ufnm;
       if(b->uend)
       {       b->uend = NO;
               return(OK);
       }
       if((x=ftell(b->ufd))==0) return(OK);
       if(!b->useek) err(errflag,F_ERNOBKSP,bksp)
       if(b->uwrt) t_runc(b,errflag);
       if(b->url)              /* direct access, purely academic */
       {       y = x%(long)b->url;
               x -= y?y:b->url;
               fseek(b->ufd,x,0);
               return(OK);
       }
       if(!b->ufmt)            /* unformatted sequential */
       {       fseek(b->ufd,-(long)sizeof(int),1);
               fread((char *)&n,sizeof(int),1,b->ufd);
               fseek(b->ufd,-(long)n-2*sizeof(int),1);
               return(OK);
       }
       if(x==1)                        /* formatted sequential */
       {       rewind(b->ufd);
               return(OK);
       }
       while(last_char(b->ufd)!='\n'); /* slow but simple */
       return(OK);
}