The difference between const char *, char const *, char * const in C/C++

1. const char *ptr
   defines a pointer to a character constant.
   The pointer points can be modified, but the value pointed to by the pointer cannot be modified.

2. char const *ptr
   is equivalent to 1

3. char * const ptr
   defines a pointer constant to a character.
   The pointer point cannot be modified, and the value pointed to by the pointer can be modified