5 integer f_back(a) alist *a;
7 integer f_back(alist *a)
14 f__curunit = b = &f__units[a->aunit]; /* curunit for error messages */
16 f__fatal (131, "I/O recursion");
17 if(a->aunit >= MXUNIT || a->aunit < 0)
18 err(a->aerr,101,"backspace");
19 if(b->useek==0) err(a->aerr,106,"backspace");
20 if((f = b->ufd) == NULL) {
21 fk_open(1, 1, a->aunit);
30 f = b->ufd; /* t_runc might change b->ufd */
32 err(a->aerr,errno,"backspace");
41 (void) fseek(f,x,SEEK_SET);
46 { fseek(f,-(long)sizeof(uiolen),SEEK_CUR);
47 fread((char *)&n,sizeof(uiolen),1,f);
48 fseek(f,-(long)n-2*sizeof(uiolen),SEEK_CUR);
57 for(y = x; y < w; y++) {
68 err(a->aerr,(EOF),"backspace");
71 fseek(f, z, SEEK_SET);