const in C vs const in C++

Question

The given code compiles in C but fails in C++.

int main()
{
   const int x; /* uninitialized const compiles in C but fails in C++*/
}

What

Answer 1

Note that there is a legitimate use of an uninitialized, const-qualified object of automatic storage duration: its address can be taken and used as a unique key for labeling recursion levels in a recursive function. This is somewhat obscure, but worth noting. C makes this use efficient, while C++ requires you waste time and code size on initializing it. (In theory the compiler could perhaps determine that the value is never used and optimize out the initialization, but since you're passing around a pointer, that would be rather difficult to prove.)