pointer-to-const conversion in C

Question

The following code compiles without warning on GCC but gives a warning in Visual Studio 2005.

const void * x = 0;
char * const * p = x;

x p

Answer 1

warning C4090: 'initializing' : different 'const' qualifiers

You cannot cast const void to char *const or even char *. By dereferencing p, you can now modify *(char *)(*x). This is a little known subtlety about pointers in C.

A working type for p would be:

char const **p = x;

And yes, I put const on the right like a man.