void指针强转结构体指针问题

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1.程序，test.c

#include <stdio.h>
#include <stdlib.h>

typedef unsigned long u32; //64位机器为8字节，32位机器为4字节
typedef struct my_struct{
  u32 a;
  u32 b;
  u32 c;
}mystruct;

int main(){
  void *test;
  test = NULL;
  test = malloc(1);
  printf("test is %lx
",test);
  #define GPIO ((mystruct *)(test))
  GPIO->a = 10;
  GPIO->b = 20;
  GPIO->c = 30;
  printf("(&(GPIO->a)) is %lx
",(&(GPIO->a)));
  printf("(&(GPIO->b)) is %lx
",(&(GPIO->b)));
  printf("(&(GPIO->c)) is %lx
",(&(GPIO->c)));
  printf("GPIO->a is %d
",GPIO->a);
  printf("GPIO->b is %d
",GPIO->b);
  printf("GPIO->c is %d
",GPIO->c);
  free(test);
  test = NULL;
  return 0;
}

3.结果./test

test is 17f2010
(&(GPIO->a)) is 17f2010
(&(GPIO->b)) is 17f2018
(&(GPIO->c)) is 17f2020
GPIO->a is 10
GPIO->b is 20
GPIO->c is 30