Const *ptr PTR

1. const int *ptr = NULL; <=> int const *PTR = NULL;

1) Represents a pointer variable to a symbolic constant, and the pointer variable itself is not const so it can point to other variables.

2) The role of Const can be seen as "forbidden by *ptr" To change the value of the variable that the PTR points to, but the variable being pointed to can change its own definition .

eg:const int i = 1, int j = 2;

PTR = &i; Ok

*ptr = +//Error

i = 2//Error i is const

PTR = &j; Ok

*ptr = 28; Error

j = 3; Ok

2. const int *PTR vs int * const PTR;

1) to distinguish between the above two forms of emphasis on the relative position of the const and *:

Const indicates "pointer to symbol constant" before *

Const represents "a constant pointer to a variable of type int" after *

Note: if declared as int * Const PTR = NULL, the value of PTR cannot be changed to point to another variable.

However, you can modify the variable that it points to (if it points to it) by *ptr.

2) Memorizing skills

See if the const modifier is *ptr or ptr?

When const can be assumed to be a const modifier before * *ptr, the value of *ptr is immutable and the value of PTR is variable

When const is assumed to be a const-modified PTR after *, the value of PTR is immutable and the value of *PTR is variable

Const modifies who, whose value cannot be changed.

3. const int * const PTR;

1) indicates "constant pointer to int type symbol constant"

2) const modifies the *ptr to indicate that the value of the pointer to the variable cannot be modified by *ptr

It also modifies the PTR to indicate that the value in the PTR can no longer be modified to point to another variable

Const *ptr PTR