const usage with pointers in C

I am going over C and have a question regarding const usage with pointers. I understand the following code:

const char *someArray

This is defining a pointer that points to types of char and the const modifier means that the values stored in someArray cannot be changed. However, what does the following mean?

char * const array

Is this an alternate way of specifying a parameter that is a char pointer to an array named "array" that is const and cannot be modified?

Lastly, what does this combination mean:

const char * const s2

For reference, these are taken from the Deitel C programming book in Chapter 7 and all of these are used as parameters passed to functions.

Solution 1:

const char* is, as you said, a pointer to a char, where you can't change the value of the char (at least not through the pointer (without casting the constness away)).

char* const is a pointer to a char, where you can change the char, but you can't make the pointer point to a different char.

const char* const is a constant pointer to a constant char, i.e. you can change neither where the pointer points nor the value of the pointee.

Solution 2:

From what is the difference between const int*, const int * const, int const *:

Read it backwards...

int* - pointer to int
int const * - pointer to const int
int * const - const pointer to int
int const * const - const pointer to const int

Solution 3:

//pointer to a const
void f1()
{
    int i = 100;
    const int* pi = &i;
    //*pi = 200; <- won't compile
    pi++;
}

//const pointer
void f2()
{
    int i = 100;
    int* const pi = &i;
    *pi = 200;
    //pi++; <- won't compile
}

//const pointer to a const
void f3()
{
    int i = 100;
    const int* const pi = &i;
    //*pi = 200; <- won't compile
    //pi++; <- won't compile

}