Difference between pointer and const qualifier const int * p and int * const p

First look at const int a = 2; the value of a is read-only.

The difference between const int * p and int * const p ,.

It can be understood as follows: divide the variable into two parts based on the "*" as the demarcation point to see who the const modifier is.

Const int * p: const modifies int, so const int is regarded as a type. Obviously, this type of memory is read-only. P pointer itself is not read-only

Int * const p: const modifies p, which is read-only like a above. The memory pointing to is not read-only and read/write.

In addition, the const int * p and int const * p statements are the same.

Example:

 

[Cpp] # include <stdio. h>
 
Static const int num = 5;
Static int a [5] = {0, 1, 2, 3, 4 };
 
Extern void print_all_address_value (const int p [], const int p1 []); // the advantage of this parameter is that data will not be changed during access ..
Extern int get_value (const int * const a); // the advantage of this parameter is that the data is not changed during access and the required data is obtained, instead of unexpected data.
Extern int set_value (int * const a, const int value); // the benefit of this parameter is that we need to change the changed data.
<PRE class = cpp name = "code">
Void main (){
Int * p, * p1;
P =;
P1 = & a [0];
Print_all_address_value (p, p1 );
Set_value (p + 1, 9 );
Get_value (p1 + 1 );
Printf ("value p1 = % d \ n", get_value (p + 1 ));
}
 
Extern void print_all_address_value (const int p [], const int p1 []) {
Int I = 0;
For (I = 0; I <num; I ++ ){
Printf ("for address a = % p, p = % p, p1 = % p \ n", & a [I], p, p1 );
Printf ("for value a = % d, p = % d, p1 = % d \ n", a [I], * p, * p1 );
P ++;
P1 ++;
}
}
 
Extern int get_value (const int * const ){
Return *;
}
Extern int set_value (int * const a, const int value ){
* A = value;
Return *;
}
</PRE>
<P> </P>
<PRE> </PRE>