Q70 What is the difference between const char *ptr, char * const ptr, and const char * const ptr?
const char *ptr – This is a pointer to a constant char. One cannot change the value pointed at by ptr, but can change the pointer p itself see an example given below:
*ptr = ‘A’; /* illegal operation */
ptr = “Gyantoday”; /* legal operation */
Note that even char const *p is the same!
char * const ptr – Here pointer is a constant. The data can be changed but we cannot assigned new address to the pointer. Example given below:
char * const ptr = “Gyantoday”;
*ptr = “Pointer”; /* Legal operation */
++ptr; /* Illegal operation- error: increment of read-only variable ‘ptr’ */
const char const *ptr – Here pointer and value pointed by pointer both are constant. See an example below:
const char const *ptr = “Gyantoday”;
*ptr = “Pointer” /* illegal operation */
++ptr; /* illegal operation */