Question

I have this code

int main()
{
    char A = 'E';

    const char * i;

    i = &A;

    A = 'B';

}

which actually compiles with MSVC, why?
Isn’t a const char * supposed to point to a constant character variable? Why can I change A to ‘B’ in the last line?

Am I missing something?

Answer 1

There is a difference between a constant of type char being pointed to (a.k.a. the pointee) and a constant pointer of type char*. If you want to protect a pointer from (accidental) modification, you can declare it constant:

char* p = '...';
char* const cp = 'Hello, World!'; // a constant pointer
cp[1] = ','; // okay, the pointee is not constant
cp = p;      // error, the pointer is constant

A variable pointer to a constant can change:

char *p = '...';
const char* pc = 'Hello, World!'; // pointer to a constant
pc[1] = ','; // error, the pointee is constant
pc = p;      // okay

And finally, you can declare a constant pointer to a constant with

const char* const cpc = 'Hello, World!';
cpc[1] = 'a'; // error, pointee cannot change
cpc = p;      // error, pointer cannot change

This is from §5.4.1 of “The C++ Programming Language”, Stroustrup.

You can change A to 'B' in the last line, because A is of type char and therefore can be changed. It isn’t declared a const char, which would prevent you from doing so.