changing the value of const variable in C++ [duplicate]

Answer 1

Here's a refresher, it should be noted that this is in C. This is a deceptively tricky underpinnings of the usage of a variable or pointer using the const keyword. This highlights the difference between the pointer variable foo and how the meaning of it can change by using the said keyword.

char const *foo;

char * const foo;

const char *foo;

The first and last declarations, makes the data pointed to by ‘foo’ read-only, but, you can change the address pointed to by ‘foo’ e.g.

const *char foo; /* OR char const *foo */

char str[] = "Hello";

foo = &str[0]; /* OK! */

foo[1] = 'h'; /* BZZZZTTT! Compile Fails! */

The middle declaration in the above, makes the pointer read-only, i.e. you cannot change the address of the data pointed to by ‘foo’

char * const foo;

char str[] = "Hello";

foo = &str[0]; /* BZZZZTTT! Compile Fails! */

Answer 2

const_cast doesn't take away the const-ness of a variable as defined. If you were to pass a non-const variable by reference in to a method taking a const reference like void foo(const int& x) then you could use const_cast to modify the value of x within foo, but only if the variable you actually passed in was not const in the first place.