Question

Suppose some memory location 0xF0000 contains four character string "four" .

so is this valid:

char *mem = (char*) 0xF0000;

and then is mem[0] == ‘f’ ?

Answer 1

Sure it is. If the memory is mapped with the correct permissions (write) it should make no difference whatsoever to the operating system.

An easy way to test this is using gdb. You can break and change the value of mem an make it point to some memory, right before an instruction tries to change it.

In particular, don’t try to modify a string literal (char *readonly = "mystr");