Add Chapter 27, exercise 3

chapter27/chapter27_ex03.c

@@ -0,0 +1,267 @@
+/* Chapter 27, exercise 3: "pretty up" the intrusive List example from 27.9 */
+
+#include<stdio.h>
+#include<stdlib.h>
+
+#define ERROR_PTR (struct Link*)0xDEADBEEF
+
+struct List {
+    struct Link* first;
+    struct Link* last;
+};
+
+struct Link {
+    struct Link* pre;
+    struct Link* suc;
+};
+
+struct Name {
+    struct Link lnk;    /* the Link required by List operations */
+    char* p;            /* the name string */
+};
+
+struct Name* make_name(char* n)
+{
+    struct Name* p = (struct Name*)malloc(sizeof(struct Name));
+    p->p = n;
+    return p;
+}
+
+/* initialize lst to empty; return 0 if okay, -1 if not */
+int init(struct List* lst)
+{
+    if (lst==0) return -1;
+    lst->first = lst->last = 0;
+    return 0;
+}
+
+struct List* create()   /* make a new empty list on free store */
+{
+    struct List* lst = (struct List*)malloc(sizeof(struct List));
+    init(lst);
+    return lst;
+}
+
+/* free all elements of lst; return 0 if okay, -1 if not */
+int clear(struct List* lst) {
+    if (lst==0) return -1;
+    {
+        struct Link* curr = lst->first;
+        while (curr) {
+            struct Link* next = curr->suc;
+            free(curr);
+            curr = next;
+        }
+        lst->first = lst->last = 0;
+    }
+    return 0;
+}
+
+/* free all elements of lst; then free lst; return 0 if okay, -1 if not */
+int destroy(struct List* lst)
+{
+    if (lst==0) return -1;
+    clear(lst);
+    free(lst);
+    return 0;
+}
+
+/* add p at end of lst; return 0 if okay, -1 if not */
+int push_back(struct List* lst, struct Link* p)
+{
+    if (lst==0) return -1;
+    {
+        struct Link* last = lst->last;
+        if (last) {
+            last->suc = p;  /* add p after last */
+            p->pre = last;
+        }
+        else {
+            lst->first = p; /* p is the first element */
+            p->pre = 0;
+        }
+        lst->last = p;
+        p->suc = 0;
+    }
+    return 0;
+}
+
+/* add p at front of lst; return 0 if okay, -1 if not */
+int push_front(struct List* lst, struct Link* p)
+{
+    if (lst==0) return -1;
+    {
+        struct Link* first = lst->first;
+        if (first) {
+            first->pre = p; /* add p before first */
+            p->suc = first;
+        }
+        else {
+            lst->last = p;  /* p is the last element */
+            p->suc = 0;
+        }
+        lst->first = p;
+        p->pre = 0;
+    }
+    return 0;
+}
+
+/* insert q before p in lst; return 0 if okay, -1 if not */
+int insert(struct List* lst, struct Link* p, struct Link* q)
+{
+    if (lst==0) return -1;
+    if (q==0) return 0; /* insert nothing */
+
+    if (p == lst->first)    /* works also for empty list */
+        push_front(lst,q);  /* q becomes new first element */
+    else {
+        q->suc = p;
+        q->pre = p->pre;
+        p->pre->suc = q;
+        p->pre = q;
+    }
+    return 0;
+}
+
+/* remove p from lst; return a pointer to the link after p if ok, ERROR_PTR if
+   not */
+struct Link* erase(struct List* lst, struct Link* p)
+{
+    if (lst==0) return (struct Link*)ERROR_PTR;
+    if (p==0) return 0; /* OK to erase(0) */
+
+    if (p == lst->first) {
+        if (p->suc) {
+            lst->first = p->suc;    /* the successor becomes first */
+            p->suc->pre = 0;
+            return p->suc;
+        }
+        else {
+            lst->first = lst->last = 0; /* the list becomes empty */
+            return 0;
+        }
+    }
+    else if (p == lst->last) {
+        if (p->pre) {
+            lst->last = p->pre; /* the predecessor becomes last */
+            p->pre->suc = 0;
+            return 0;
+        }
+        else {
+            lst->first = lst->last = 0; /* the list becomes empty */
+            return 0;
+        }
+    }
+    else {
+        p->suc->pre = p->pre;
+        p->pre->suc = p->suc;
+        return p->suc;
+    }
+}
+
+/* return link n "hops" before or after p if ok, ERROR_PTR if not */
+struct Link* advance(struct Link* p, int n)
+{
+    if (p==0) return ERROR_PTR;
+    if (n > 0) {
+        while (n--) {
+            if (!p->suc)
+                return ERROR_PTR;
+            p = p->suc;
+        }
+        return p;
+    }
+    else if (n < 0) {
+        while (n++) {
+            if (!p->pre)
+                return ERROR_PTR;
+            p = p->pre;
+        }
+        return p;
+    }
+    else return p;  /* n == 0 */
+}
+
+/* convenience functions for Name Links */
+
+int push_back_name(struct List* lst, char* n)   /* push back name */
+{
+    return push_back(lst,(struct Link*)make_name(n));
+}
+
+int push_front_name(struct List* lst, char* n)  /* push front name */
+{
+    return push_front(lst,(struct Link*)make_name(n));
+}
+
+int insert_name(struct List* lst, struct Link* p, char* n)  /* insert name */
+{
+    return insert(lst,p,(struct Link*)make_name(n));
+}
+
+
+void print_lst(struct List* lst)
+{
+    int count = 0;
+    struct Link* curr = lst->first;
+    for (; curr!=0; curr = curr->suc) {
+        ++count;
+        printf("element %d: %s\n",count,((struct Name*)curr)->p);
+    }
+}
+
+int main()
+{
+    struct List* names = create();
+
+    printf("Pushing back three names:\n");
+    push_back_name(names,"Norah");
+    push_back_name(names,"Annemarie");
+    push_back_name(names,"Kris");
+    print_lst(names);
+
+    printf("\nErasing second name:\n");
+    erase(names,advance(names->first,1));
+    print_lst(names);
+
+    printf("\nPushing front one name:\n");
+    push_front_name(names,"Bjarne");
+    print_lst(names);
+
+    printf("\nInsert names at front and before last element:\n");
+    insert_name(names,names->first,"Herbert");
+    insert_name(names,names->last,"Scott");
+    print_lst(names);
+
+    printf("\nErasing first element until list empty:\n");
+    while (erase(names,names->first));
+    print_lst(names);
+
+    printf("\nInserting one element so we have something to destroy:\n");
+    insert_name(names,names->first,"Andrei");
+    print_lst(names);
+
+    printf("\nDestroying list\n\n");
+    destroy(names);
+
+    /* test error handling */
+    int err_code = init(0);
+    if (err_code==-1) printf("error in init()\n");
+    names = create();
+    err_code = push_front_name(0,"Bjarne");
+    if (err_code==-1) printf("error in push_front()\n");
+    err_code = push_front_name(names,"Bjarne");
+    if (err_code==-1) printf("error in push_front()\n");    /* OK */
+    struct Link* err_ptr = erase(0,0);
+    if (err_ptr==ERROR_PTR) printf("error in erase()\n");
+    err_ptr = erase(names,names->first);
+    if (err_ptr==ERROR_PTR) printf("error in erase()\n"); /* OK */
+    err_code = clear(0);
+    if (err_code==-1) printf("error in clear()\n");
+    err_code = clear(names);
+    if (err_code==-1) printf("error in clear()\n");
+    err_code = destroy(0);
+    if (err_code==-1) printf("error in destroy()\n");
+    err_code = destroy(names);
+    if (err_code==-1) printf("error in destroy()\n");
+}