Combination of const and pointer

One .const Analysis of several cases of combination with pointer ：
Definition int a=1;int b=2;
1.int const *p = const int *p; //p It can change itself , But it points to int Type data value is immutable
understand ：p Is a pointer variable , The pointer is the address , therefore p What is stored is the address , The definition form here represents p It's variable in itself , That is to say p Value （ Address ） Is variable , But it can't be modified p( Address ) Value stored in , That is to say p variable , however *p immutable .
therefore ：
   int const *p=&a; p=&b; Correct use , because p In itself ( Address ) variable .
   int const *p=&a; *p=3; Wrong use , because p The value of the point （ The value in the address ） immutable .

2.int * const p; //p It's immutable , But it points to int Type data value is variable
understand ：p The value of itself is an address , therefore const p Express p（ Address ） immutable , but p Point to data （ The value stored in the address ） Is variable, that is p immutable , but *p Is variable .
therefore ：
   int * const p=&a; *p=3; Correct use , because *p（ The contents of the address ） variable .
   int * const p=&a; p=&b; Wrong use , because p In itself （ Address ） immutable .

3.const int * const p; //p It's immutable ,p Point to the int Type data values are also immutable
understand ： Combined with the above two situations, it is not difficult to analyze , here p Oneself （ Address ） immutable , And point to the data value （ The value in the address ） Also immutable .
therefore ：
   const int * const p=&a; *p=3; Wrong use , because *p（ The contents of the address ） immutable .
   const int * const p=&a; p=&b; Wrong use , because p（ In the address ） It's immutable .

summary ：const Decorating pointers has a wide range of uses , For example, we are making string arrays copy You will use ：void stcopy(char *des,const char *src); Use here const I don't want to decorate src The value of the array is changed in the function .
about const There are the following ways to use form memory in combination with pointers ： It mainly depends on const It's direct modification p still *p, Simply put, look const The modifier is in * Front or back , Feel for yourself .