const char * const versus const char *?

1. Mutable pointer to a mutable character

   char *p;
   

2. Mutable pointer to a constant character

   const char *p;
   

3. Constant pointer to a mutable character

   char * const p; 
   

4. Constant pointer to a constant character

   const char * const p;
   

const char * const means pointer as well as the data the pointer pointed to, are both const!

const char * means only the data the pointer pointed to, is const. pointer itself however is not const.

Example.

const char *p = "Nawaz";
p[2] = 'S'; //error, changing the const data!
p="Sarfaraz"; //okay, changing the non-const pointer. 

const char * const p = "Nawaz";
p[2] = 'S'; //error, changing the const data!
p="Sarfaraz"; //error, changing the const pointer. 

The latter prevents you from modifying the_string inside print_string. It would actually be appropriate here, but perhaps the verbosity put off the developer.

char* the_string : I can change which char the_string points to, and I can modify the char to which it points.

const char* the_string : I can change which char the_string points to, but I cannot modify the char to which it points.

char* const the_string : I cannot change which char the_string points to, but I can modify the char to which it points.

const char* const the_string : I cannot change which char the_string points to, nor can I modify the char to which it points.