无法更新指针值

Question

我可能对指针的工作原理存在根本性的误解，但我认为我可以为指针分配一个变量值，但是每当我打印指针的取消引用值时，它始终为 0 而不是“timestamp”的值。

volatile uint32_t *myAddress = (volatile uint32_t*)0x12341234;

uint32_t timestamp = 0x1111;

*myAddress = timestamp;

Answer 1

Cannot update pointer value

你的意思是不能更新指向的值

做

 volatile uint32_t *myAddress = (volatile uint32_t*)0x12341234;

 uint32_t timestamp = 0x1111;

 *myAddress = timestamp;

您使用(很可能)无效地址 0x12341234，以推断它具有未定义的行为

做类似的事情:

uint32_t v;

volatile uint32_t *myAddress = &v;

uint32_t timestamp = 0x1111;

*myAddress = timestamp;
// now v values 0x1111

---

示例:

#include <stdio.h>
#include <stdint.h>

int main()
{
  uint32_t v = 0;

  volatile uint32_t *myAddress = &v;

  uint32_t timestamp = 0x1111;

  *myAddress = timestamp; // now v values 0x1111

  printf("0x%x 0x%x\n", (unsigned) v, (unsigned) *myAddress);

  return 0;
}

编译和执行:

pi@raspberrypi:/tmp $ gcc -pedantic -Wextra -Wall c.c
pi@raspberrypi:/tmp $ ./a.out
0x1111 0x1111
pi@raspberrypi:/tmp $