c语言.txt

内存空间访问：
指针的核心：
1.分配多大指针空间
32位系统(32位)：
2^10b = 1K
2^20  = 1M
2^30  = 1G
2^32  = 4G
2.地址指向资源的读取解析方法

abc@DESKTOP-SV1JI86:~/clan$ cat test.c                                                                                  #include <stdio.h>

int main() {
  int a = 0xA1B2C3D4;
  int *p1;
  char *p2;
  p1 = &a;
  //指针值为地址的最小值  不管大端小端存储;
  p2 = &a;
  printf("the p1 sizeof is %lu\n",sizeof(p1));
  printf("the p2 sizeof is %lu\n",sizeof(p2));
  printf("the p1 value is %x\n",*p1);
  printf("the p2 value is %x\n",*p2);
}
abc@DESKTOP-SV1JI86:~/clan$ gcc test.c
test.c: In function ‘main’:                                                                                             test.c:9:6: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]                              p2 = &a;                                                                                                                   ^                                                                                                                 abc@DESKTOP-SV1JI86:~/clan$ ./a.out
the p1 sizeof is 8
the p2 sizeof is 8
the p1 value is a1b2c3d4
the p2 value is ffffffd4

指针指向的内存空间一定要保证合法性

指针修饰符：
const:
const char *p = char const *p;   ==>>字符串
char * const p = char *p const;    ==>>硬件资源
const char * const p

volatile 不优化
volatile char *p;
一般说来，volatile关键字用在如下的几个地方。
(1)中断服务程序中修改的供其他程序检测的变量需要加volatile。
(2)多任务环境下各任务间共享的标志应该加volatile。
(3)存储器映射的硬件寄存器通常也要加volatile说明，因为每次对它的读写都可能有不同意义。