Use of (void) before a function call [duplicate]

A cast to void can have semantic effect in one case: where a value is an operand of the comma operator and overrides the comma operator, a cast to void will suppress it:

struct S {
  int operator,(int) { return 0; }
};
std::cout << (S(), 42) << '\n';           // prints '0'
std::cout << ((void) S(), 42) << '\n';    // prints '42'