const_cast
is safe only if you’re casting a variable that was originally non-const
. For example, if you have a function that takes a parameter of a const char *
, and you pass in a modifiable char *
, it’s safe to const_cast
that parameter back to a char *
and modify it. However, if the original variable was in fact const
, then using const_cast
will result in undefined behavior.
void func(const char *param, size_t sz, bool modify)
{
if(modify)
strncpy(const_cast<char *>(param), sz, "new string");
printf("param: %s\n", param);
}
...
char buffer[16];
const char *unmodifiable = "string constant";
func(buffer, sizeof(buffer), true); // OK
func(unmodifiable, strlen(unmodifiable), false); // OK
func(unmodifiable, strlen(unmodifiable), true); // UNDEFINED BEHAVIOR