c语言一点小觉悟(1)

  1 #include <stdio.h>
  2 
  3 int a = 0x12345678;
  4 int a2 = 0x12345678;
  5 int a3 = 0x12345678;
  6 int a4 = 0x12345678;
  7 int main()
  8 {
  9     int b = 0x12345678;
 10     int b2 = 0x12345678;
 11     int b3 = 0x12345678;
 12     int b4 = 0x12345678;
 13     char *p1,*p2,*p3,p5;
 14     int *p4,p6;
 15     
 16     
 17     char *c = "hello";
 18     
 19     p1 = &b;
 20     *p2 = &b;
 21     p3 = &a;
 22     p4 = &a;
 23     *p4 = *p4+1;
 24     p5 = a;
 25     p6 = a;
 26     printf("hello world\n");
 27     printf("int a addr is: %p\n",&a);
 28     printf("int a2 addr is: %p\n",&a2);
 29     printf("int a4 addr is: %p\n",&a3);
 30     printf("int a3 addr is: %p\n",&a4);
 31     printf("int b addr is: %p\n",&b);
 32     printf("int b2 addr is: %p\n",&b2);
 33     printf("int b3 addr is: %p\n",&b3);
 34     printf("int b4 addr is: %p\n",&b4);
 35     printf("int main addr is: %p\n",main);
 36     printf("===========================\n");
 37     
 38     printf("pointer p1 addr is: %p\n",p1);
 39     printf("*p1 addr is: %p\n",*p1);
 40     printf("pointer p3 addr is: %p\n",p3);
 41     printf("*p3 addr is: %p\n",*p3);
 42     printf("pointer p4 addr is: %p\n",p4);
 43     printf("*p4 addr is: %p\n",*p4);
 44     printf("pointer p2 addr is: %p\n",p2);
 45     printf("*p2 addr is: %p\n",*p2);
 46     printf("===========================\n");
 47     printf("char p5 is : %p\n",p5);
 48     printf("int p6 is:%p\n",p6);
 49     
 50     printf("============================\n");
 51     printf("str addr is: %p\n","hello");
 52     printf("str addr is: %p\n",&"hello");
 53     printf("============================\n");
 54     printf("str addr is: %s\n",c);
 55     printf("str addr is: %p\n",c);
 56     printf("str addr is: %p\n",&c);
 57     
 58     return 0;
 59 }
 60 /*
 61 C:\Users\shuai\Desktop\c>gcc -o build 001.c & build
 62 001.c: In function 'main':
 63 001.c:14:5: warning: assignment from incompatible pointer type [-Wincompatible-p
 64 ointer-types]
 65   p1 = &b;
 66      ^
 67 001.c:15:6: warning: assignment makes integer from pointer without a cast [-Wint
 68 -conversion]
 69   *p2 = &b;
 70       ^
 71 001.c:16:5: warning: assignment from incompatible pointer type [-Wincompatible-p
 72 ointer-types]
 73   p3 = &a;
 74      ^
 75 hello world
 76 int a addr is: 0x402008
 77 int a2 addr is: 0x40200c
 78 int a4 addr is: 0x402010
 79 int a3 addr is: 0x402014
 80 int b addr is: 0x28cc44
 81 int b2 addr is: 0x28cc40
 82 int b3 addr is: 0x28cc3c
 83 int b4 addr is: 0x28cc38
 84 int main addr is: 0x4011d0
 85 ===========================
 86 pointer p1 addr is: 0x28cc44
 87 *p1 addr is: 0x78
 88 pointer p3 addr is: 0x402008
 89 *p3 addr is: 0x79
 90 pointer p4 addr is: 0x402008
 91 *p4 addr is: 0x12345679
 92 pointer p2 addr is: 0x612b5060
 93 *p2 addr is: 0x44
 94 ===========================
 95 char p5 is : 0x79
 96 int p6 is:0x12345679
 97 ============================
 98 str addr is: 0x403060
 99 str addr is: 0x403060
100 ============================
101 str addr is: hello
102 str addr is: 0x403060
103 str addr is: 0x28cc40
104 
105 
106 */
107 
108 /*
109 结论:
110     1 系统中全局数据空间地址从小往大排列
111       系统中栈空间地址从栈顶往小排列
112       其中貌似main最先初始化,然后才有了后续事件
113     2 *p=*p+1 实际上是指针+1 等效于*p=*(p+1) 即对指针操作
114       *p=(*p)+1 指的是p地址上的数据+1 即对数据操作 注意两者不同 
115     3 char *c="hello" ("%p\n",c)和("%p\n","hello")和("%p\n",&"hello")结果一样都是常量"hello"地址
116       ("%p\n",&c)取得是c的地址
117       ("%s\n",c)输出hello
118     4 *p=&b慎用,看起来不伦不类.并且结果未知,(*p==b?)
119       推荐使用p=&b,再*p即是b的值(*p==b为真)
120     
121     
122 */