The addresses of array elements
Use & operator to get the addresses of elements

数组中每个元素都放在内存中

| image.png | ```cpp

include

using namespace std;

struct Student { char name[4]; int born; bool male; };

int main() { // Part One Student students[128]; Student p0 = &students[0]; Student p1 = &students[1]; Student p2 = &students[2]; Student p3 = &students[3];

  1. printf("p0 = %p\n", p0);
  2. printf("p1 = %p\n", p1);
  3. printf("p2 = %p\n", p2);
  4. printf("p3 = %p\n", p3);
  6. //the same behavior
  7. students[1].born = 2000;
  8. p1->born = 2000;
  10. // Part Two
  11. // You can consider an array name as a pointer
  12. printf("&students = %p\n", &students);
  13. printf("students = %p\n", students);
  14. printf("&students[0] = %p\n", &students[0]);
  16. Student *p = students;
  17. p[0].born = 2000;
  18. p[1].born = 2001;
  19. p[2].born = 2002;
  21. printf("students[0].born = %d\n", students[0].born);
  22. printf("students[1].born = %d\n", students[1].born);
  23. printf("students[2].born = %d\n", students[2].born);
  25. return 0;

}

// results // p0 = 0x7ffd3e5b2f10 // p1 = 0x7ffd3e5b2f1c // p2 = 0x7ffd3e5b2f28 // p3 = 0x7ffd3e5b2f34 // &students = 0x7ffd3e5b2f10 // students = 0x7ffd3e5b2f10 // &students[0] = 0x7ffd3e5b2f10 // students[0].born = 2000 // students[1].born = 2001 // students[2].born = 2002

 |
| --- | --- |

Pointer arithmetic 指针的代数操作

- `p + num` or `num + p` points to the **num-th element **of the array p.
   - 对指针p的地址进行偏移，**偏移量为num个元素**，不是加一个字节
- `p - num` points to the -num-th element.
| ![image.png](https://cdn.nlark.com/yuque/0/2021/png/353587/1636875221979-52f76ac3-5a5b-4cee-94c2-c584eaf1f562.png#clientId=u215afbef-e0c2-4&from=paste&height=477&id=u93764ca5&margin=%5Bobject%20Object%5D&name=image.png&originHeight=477&originWidth=489&originalType=binary&ratio=1&size=22325&status=done&style=none&taskId=ue44975a5-0d1c-41c3-bdee-e3b6d2be034&width=489) | ```cpp
#include <iostream>
using namespace std;

#define PRINT_ARRAY(array, n)           \
    for (int idx = 0; idx < (n); idx++) \
        cout << "array[" << idx << "] = " << (array)[idx] << endl;

int main()
{
    int numbers[4] = {0, 1, 2, 3};
    PRINT_ARRAY(numbers, 4)

    int *p = numbers + 1; // point to the element with value 1
    p++;                  // point to the element with value 2

    cout << "numbers = " << numbers << endl;
    cout << "p = " << p << endl;
    cout << "p0 = " << p[0] << endl;

    *p = 20;       //change 2 to 20
    *(p - 1) = 10; //change 1 to 10
    p[1] = 30;     //change 3 to 30 ？？？

    PRINT_ARRAY(numbers, 4)

    return 0;
}

// array[0] = 0
// array[1] = 1
// array[2] = 2
// array[3] = 3
// numbers = 0x7fff47f36170
// p = 0x7fff47f36178
// p0 = 2
// array[0] = 0
// array[1] = 10
// array[2] = 20
// array[3] = 30

| | —- | —- |

指针的代数运算也很容易发生越界，一定注意。

#include <iostream>
using namespace std;

int main()
{
    int a;
    int num = 0;
    int *p = &num;

    p[-1] = 2;    //out of bound
    p[0] = 3;     //okay
    *(p + 1) = 4; //out of bound

    cout << "num = " << num << endl;

    return 0;
}

Differences between a pointer and an array

  • Array is a constant pointer.
  • The total size of all elements in an array can be got by operator sizeof
  • sizeof operator to a pointer will return the size of the address (4 or 8) ```cpp int numbers[4] = {0, 1, 2, 3}; int p = numbers; cout << sizeof(numbers) << endl; //4sizeof(int) cout << sizeof(p) << endl; // 4 or 8 cout << sizeof(double *) << endl; // 4 or 8

```