_GETTING A HANDLE ON VIRTUAL MEMORY_ by Walter Bright [LISTING ONE] /* Compile with: ZTC wc -ml */ /* (Use large model so strcmp() can handle far pointers.) */ #include #include #include #include #include struct tree { char __handle *word; int count; struct tree __handle *left; struct tree __handle *right; }; int readword(char *w, int nbytes) { int c; do { c = getchar(); if (c == EOF) return 0; } while (!isalpha(c)); do { if (nbytes > 1) { *w++ = c; nbytes--; } c = getchar(); } while (isalnum(c)); *w = 0; return 1; } void tree_insert(struct tree __handle * __handle *pt, char *w) { int cmp; struct tree __handle *p; while ((p = *pt) != NULL) { if ((cmp = strcmp(w,p->word)) == 0) goto gotit; pt = (cmp < 0) ? &p->left : &p->right; } p = (struct tree __handle *) handle_calloc(sizeof(struct tree)); if (!p || (p->word = handle_strdup(w)) == NULL) { printf("Out of memory\n"); exit(EXIT_FAILURE); } *pt = p; gotit: p->count++; } tree_print(struct tree __handle *p) { while (p) { tree_print(p->left); printf("%5d %s\n",p->count,(char far *)p->word); p = p->right; } } tree_free(struct tree __handle *p) { struct tree __handle *pn; while (p) { handle_free(p->word); tree_free(p->left); pn = p->right; handle_free(p); p = pn; } } main() { struct tree __handle *root = NULL; char word[32]; while (readword(word,sizeof(word))) tree_insert(&root, word); tree_print(root); tree_free(root); return EXIT_SUCCESS; } [Figure 1: Typical pointer types used in most PC implementations of C] void *p; /* pointer type is default for the memory model */ char far *pc; /* far (segment and offset pair) pointer */ int near *p; /* near (offset only, segment is assumed) */ [Figure 2: Converting pointers from handle to far] R 65,T 5 int __handle *h; struct A __handle *h2; int far *f; int i; extern void func(int far *pi); f = h; *h = i; h[3] = *f; i = *(h + 6); h2->b = i; func(h); h = (int far *) h; [Figure 3: Example showing that the optimizer is handle aware] struct { int a,b; } __handle *h; h->a = 1; h->b = 2; /* Converted code */ struct { int a,b; } __handle *h, far *p; p = h; p->a = 1; p->b = 2;