单链表相关操作之C语言实现：插入，删除，倒转，复制，查找。。。

typedef struct node  {      node *next; /* pointer to next element in list */      char data;  }node, *pnode, **ppnode;   // define two types  // create an empty node  pnode list_createNullNode()  {      pnode p1;      if (p1 = (pnode)malloc(sizeof(node)))      {          p1->next = NULL;      }      return p1;  }  // create a node with data  pnode list_createNode(char c)  {      pnode p1;      if (p1 = (pnode)malloc(sizeof(node)))      {          p1->data = c;          p1->next = NULL;      }      return p1;  }  // delete head  void list_removeHead(node **p)   {      pnode n = *p;      if (*p == NULL) return;      *p = (*p)->next;      free(n);  }  // delete the tail  void list_removeTail(node **p)  {         pnode n = *p;         if (*p == NULL) return;      if ((*p)->next == NULL)      {          *p = NULL;          free(n);          return;      }      while (n->next->next) n = n->next;      free(n->next);      n->next = NULL;  }  // delete a node  bool list_deleteNode(node **p, pnode n)  {      pnode m = *p;      pnode prem;      if ((*p == NULL)||(n == NULL)) return false;      if (*p == n)      {          *p = (*p)->next;          free(m);          return true;      }      prem = m;      m = m->next;      while ((m != n)&&(m != NULL))      {          prem = m;          m = m->next;      }      if (m == NULL) return false;      else      {          prem->next = m->next;          free(m);          return true;      }  }  // reverse a list using iteration  void list_reverseList(node **p)  {      if (*p == NULL) return;      pnode pren = *p;      pnode n = (*p)->next;      pnode m;      while (n != NULL)      {          m = n->next;          pren->next = n->next;          n->next = *p;          *p = n;          n = m;      }  }  node* list_reverseList(node* &head){  node* p = head;  node* prep = NULL;  node* postp = NULL;  while (p != NULL)  {    postp = p->next; // keep a record of next node    p->next = prep;    prep = p;    p = postp;  }  head = prep;  return head;}// free the whole list  bool list_freeList(pnode head)  {      pnode n;      if (head == NULL) return true;      while( head != NULL)      {          n = head;          head = head->next;          free(n);      }      return true;  }  // search data in a list  pnode list_searchData(pnode head, char c)  {      pnode n = head;      if (head == NULL) return NULL;      while (n != NULL)      {          if (n->data == c)          {              return n;          }          n = n->next;      }      return NULL;  }  // duplicate list  pnode list_duplicateList(pnode head)  {      pnode newhead;      pnode newnode;      if (head==NULL) return NULL;      newhead = list_createNode(head->data);                if (newhead == NULL) return newhead;                pnode p = head;     pnode q = newhead;      q->data = p->data;    q->next = NULL;      while(p->next != NULL)      {             newnode = list_createNode(p->next->data);          if (newnode == NULL)          {              // memory allocation failed in the middle, return NULL and free all allocated memory.              // list_emptyList(newhead);          }          q->next = newnode;          p = p->next;          q = q->next;      }      return newhead;  }  // print the whole list  void list_printList(node *p)  {      if (p == NULL)      {          printf("list is empty!\n");          return;      }      printf("The current list is: ");      while (p != NULL)      {          printf("%c ",p->data);          p = p->next;      }      printf("\n");  }  // append a data item to the end of the list  bool list_appendData(node **p, char c)  {      pnode n = list_createNode(c);      if (n==NULL) return false;      // pnode q = *p;      // if (q==NULL){q = n;  return true;}       // this doesn't work since I use local variable      if (*p==NULL)      {          *p = n;          return true;      }      pnode m = *p;      while (m->next != NULL)          m = m->next;      m->next = n;      return true;  }  // append a node to the end of the list  bool list_appendNode(node **p, node *q)  {      if (q==NULL) return false;      if (*p==NULL)      {          *p = q;          return true;      }      pnode m = *p;      while (m->next != NULL)          m = m->next;      m->next = q;      return true;  }  // insert a data item to the head of list  bool list_addData2Head(node **p, char c)  {      pnode n = list_createNode(c);      if (n == NULL)          return false;      n->next = *p;      n->data = c;      *p = n;      return true;            }   // insert a node to the head of list  bool list_addNode2Head(node **p, pnode n)  {      if (n == NULL)          return false;      n->next = *p;      *p = n;      return true;  }   int main(void)  {      node *head = NULL; //pnode head =  NULL; //pnode = 0;      pnode newhead;      pnode p1, p2;      char c;      p1 = list_createNode('d');      p2 = list_createNullNode(); p2->data = 'e';      // newhead = list_duplicateList(head);  list_printList(newhead);                if (!list_appendData(&head, 'a')) return 0;      if (!list_appendData(&head, 'b')) return 0;      if (!list_appendData(&head, 'c')) return 0;      if (!list_addData2Head(&head, 'd')) return 0;      if (!list_addNode2Head(&head, p2)) return 0;      list_printList(head); //e d a b c  /*  c = 'a';     if (list_searchData(head, c))         printf("It is in the list!/n");     else         printf("It is not in the list!/n"); */      c = 'f';      if (list_deleteNode(&head,list_searchData(head,c)))          printf("The node has been deleted!\n");      else          printf("Deleting node failed!\n");      list_printList(head);      list_reverseList(&head);      list_printList(head);      list_printList(list_reverseList(head));    list_printList(head);/*  newhead = list_duplicateList(head); list_printList(newhead);     if (list_freeList(newhead))         printf("List has been freed!/n");     else         printf("List cannot be freed!/n"); */        return 0;  }