C ++ learning (3) - Pointer

pointer

1. pointer occupies memory space

In the 32-bit operating system, 4 bytes, 8 bytes at 64

2. null pointer with a pointer field

• Null pointer: a pointer variable to point to memory spaces numbered 0

  • Uses: initialize the pointer variable

  • Note: The amount of memory is not a null pointer access

    The memory number between 0 and 255 is occupied by the system, and therefore not accessible

  int *p = NULL;
  cout << *p << endl;   //访问会报错

• Wild pointer: pointer variable points to an illegal memory space

  int *p = (int *)0x1100;    

• Null pointer and the pointer is not a wild space of our application, so do not visit

3. const pointer modification

const pointer modified in three ways:

1. const modifier pointer - pointer constant
2. const modified constant - pointer constant
3. const pointer both modified, and modified constants

• const modifier pointer - pointer constant

  int a = 10;
  const int *p = &a;

  Features: pointers can be modified, but the value of the pointer can not be modified

  *p = 20;  //×
  int b = 20;
  p = &b;   //√

• const modified constant - pointer constant

  int a = 10;
  int * const p = &a;

  Features: pointer to not change, pointer values can be changed

  *p = 20;  //√
  int b = 20;
  p = &b;   //×

• const pointer both modified, and modified constants

  int a = 10;
  const int * const p = &a;

  Features: pointers and pointer values may be modified not

  *p = 20;  //×
  int b = 20;
  p = &b;   //×

4. pointers and arrays

Data access the pointer array

int arr[3] = {1,2,3};
int *p = arr;
/* 此时*p==arr[0] */
//数组在内存中的空间是连续的，可以通过指针自加访问下一元素
p++;  
/* 此时*p==arr[1] */