C语言指针的长度和类型深入分析

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#include<stddef.h>
struct p{
  int n;
  float f;
};
int main()
{
  struct p *sptr;
  printf("sizeof *char: %d\n", sizeof(char*));
  printf("sizeof *int: %d\n", sizeof(int*));
  printf("sizeof *float: %d\n", sizeof(float*));
  printf("sizeof *double: %d\n", sizeof(double*));
  printf("sizeof *struct: %d\n", sizeof(sptr));
  return 0;
}

#include<stdio.h>
#include<stddef.h>
#include<string.h>
int main(void)
{
  char str[] = "Hello world!";
  char *pstart = str;
  char *pend = str + strlen(str);
  ptrdiff_t difp = pend - pstart;
  printf("%d\n", difp);
  return 0;
}

/* Types for `void *' pointers. */
#if __WORDSIZE == 64
# ifndef __intptr_t_defined
typedef long int        intptr_t;
# define __intptr_t_defined
# endif
typedef unsigned long int  uintptr_t;
#else
# ifndef __intptr_t_defined
typedef int          intptr_t;
# define __intptr_t_defined
# endif
typedef unsigned int    uintptr_t;
#endif

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <string.h>
#include <assert.h>

#define ID_STR_LEN  12
#define NAME_STR_LEN 10

typedef struct student
{
  char id[ID_STR_LEN];
  char name[NAME_STR_LEN];
  uint8_t age;
}student;

student * create_student()
{
  student *stu = (student *)malloc(sizeof(student));
  if (stu == NULL)
  return NULL;
  memset(stu, 0, sizeof(student));
  return stu;
}

void *free_student(student *stu)
{
  if (stu)
  free(stu);
  return 0;
}

static void init_student(student * stu)
{
  assert(stu);
  const char *id = "2013112210";
  const char *name = "Anker";
  uint8_t age = 21;
  memcpy(stu->id, id, strlen(id));
  memcpy(stu->name, name, strlen(name));
  stu->age = age;
}

static int handle_student(intptr_t handle)
{
  if (handle == 0)
  {
  return -1;
  }
  student *stu = (student*)handle;
  printf("id: %s\n", stu->id);
  printf("name: %s\n", stu->name);
  printf("age: %u\n", stu->age);
  return 0;
}

int main(void)
{
  student *stu;
  stu = create_student();
  init_student(stu);
  //将指针转换为intptr_t类型
  intptr_t handle = (intptr_t)stu;
  handle_student(handle);
  free_student(stu);
  return 0;
}