指针与const

#include <stdio.h>
#include <string.h>

typedef struct node
{
 int next;
 int data;
}*Node;

void modify(Node l)
{
  printf("l = %d, &l = %u\n",l,&l);
  l->data = 1;
  l->next = 1;
  (*l).data = 10;
  (*l).next = 100;
}

Node MM(Node l)
{
  l = new node;
  l->data = 2;
  l->next = 2;
  return l;
}

void M(Node *l) //二维指针
{
  (*l) = new node;
  (*l)->data = 12;
  (*l)->next = 12;
}
void fun1(char *pa) //相当于传值
{
   //相当与char *tmp = pa;
   printf("&pa = %u pa %d pa = %s\n", &pa, pa,pa);
   pa = "ni,mei"; //只是更改了tmp的值
   printf("%u %d %s\n", &pa, pa,pa);
}

void fun2(char **pa) //传递pa的地址
{
   *pa = "nimie"; //指向pa char *指针
}

void int1(int *p)
{
  *p = 100;

}

int main( )
{
  //下面这个等价
  const char *p;
  char const *q;
  // "hello" 为字符串常量 const char [5]
  char *c1 = "hello";
  char *tt;
  tt = c1;
  // tt为char *指针
  // *tt 为char 指向内存单位为tt的第一个字符
  tt = "wawa";
  char *const l = tt;  //对与这种只能在初始化时赋值
  const char * const m = "haha";  //指向const对象的const指针
  char c2[20] = "world";
  char c3[15];
  // 不能这样赋值， c3 = "haha", 
  p = c1;
  q = c2;
  printf("%s\n%s\n%s\n%s\n",p,q,m,l);

  int st = 10;
  int *pp = &st;
  printf("int %u %d\n",pp, *pp);

  char *pa = "now";
  printf("&pa = %u pa = %d %s\n",&pa, pa, pa);
  printf("函数1:\n");
  printf("修改之前:%s\n",pa);
  fun1(pa);  //这里相当于值传递
  printf("修改之后:%s\n", pa);

  printf("函数2:\n");
  printf("修改之前:%s\n",pa);
  fun2(&pa);
  printf("修改之后:%s\n", pa);

  Node ps = new node;
  printf("ps = %d, &ps = %d\n",ps,&ps);
  /* ps 只是一个指向Node的指针，没有申请内存
  ps->data = 2;
  ps->next = 2;
  */
  printf("%d %d\n",ps->data,ps->next);
  modify(ps);
  printf("%d %d\n",ps->data,ps->next); 
  
  Node pq;
  //printf("%d %d\n",ps->data,ps->next);
  pq = MM(pq);
  printf("%d %d\n",pq->data,pq->next); 

  //需要用二维指针
  Node pl;
  M(&pl);
  printf("%d %d\n",pl->data,pl->next); 

  int *ll = &st;
  printf("ll = %d\n",*ll);
  int1(ll);
  printf("ll = %d\n",*ll);
  return 0;
}