Basic knowledge of pointer

Restate the pointer here
The concept of pointer
* Each variable is stored in a memory address （ In bytes ） In the first few bytes ,
* The pointer , Also known as pointer variables , The size is 4 Bytes （ or 8 Bytes ） The variable of , Its content
Represents a memory address .
* Through the pointer , It can read and write the memory area of the pointer .
* If you think of every byte of memory as a room number , Then the memory address is equivalent to the room number , And the pointer
The room number is stored in the .
~ Definition of pointer
Type name * Pointer variable name
int * p;
double * pc;( Type name )// data type
char *pf;
~ Contents of pointer
int *p =(int *) 40000;
p Pointing to the address 40000, Address p It's the address 40000;
*p It means address 40000 The contents of the first few bytes
Access the memory space pointed to through the pointer
~ Pointer definition summary
T* p//T It can be any type of name , such as int double char 

p The type of T*
*p The type of ：  T
Through the expression *p , Can read and write slave address p At the beginning sizeof(T) Bytes
*p Equivalent storage address p One of the T Variable of type
* Indirect reference operators
~ Pointer usage
char ch1 ='A'
char *pc=&ch1// bring pc Point to ch1
& : Fetch address operator
&x： Variable x The address of （ Point to x The pointer to ）
For types of T The variable of x,&x Said variable x The address of （ Point to x The pointer to ）&x The type is T*

With the pointer , You have the means to freely access memory space
You don't need to pass variables , You can directly operate on the memory . Through the pointer , The memory area that the program can access is
Not limited to the data area occupied by variables .
~ Mutual assignment of pointers
Different types of pointers , If you don't cast , Cannot assign values to each other directly .
//int &pn, char *pc,char c=ox65;
pn=pc;// Type mismatch , Compilation error ,( Pointers of the same type can be assigned to each other )
pn=&c;// Type mismatch , Compile error ,
pn=(int *)&c;
int n=*pn;//n Value uncertainty ;（ Different types of pointers , Must be cast to assign values to each other ）
~ The operation of the pointer
(1) Two pointer variables of the same type , You can compare the size
    Address p1< Address p2, Equivalent p1<p2 It's worth it .
    Address p1= Address p2, Equivalent p1==p2 It's worth it
    Address p1> Address p2, Equivalent p1>p2 It's worth it
(2) Two pointer variables of the same type , You can add and subtract
    Two T* Pointer to type p1 and p2
    p1-p2=（ Address p1- Address p2）/sizeof(T)
such as int *p1,*p2;
p1=1000,p2=600;
p1-p2=(1000-600)/sizeof(int)=(1000-600)/4=100;
(3) The result of adding or subtracting an integer from a pointer variable is a pointer
p:T* A pointer to a type
n: Variable or constant of integer type
   p+n：T* Pointer to type , Pointing to the address
      Address p+n*sizeof（T）

(4) Pointer variables can be self incremented , Self reduction
   T* Pointer to type p Pointing to the address n
p++,++p:p Point to n+ sizeof(T)
p--,--p:p Point to n-sizeof（T）

(5) Pointers can use subscript operators "[]" Carry out operations
   p It's a T* Pointer to type
   n Is a variable or constant of integer type
 p[n] Equivalent to *(p+n);