C++ What is the purpose of casting to void? [duplicate]

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Multiple purposes depending on what you cast

  • Marking your intention to the compiler that an expression that is entirely a no-op is intended as written (for inhibiting warnings, for example)
  • Marking your intention to to the compiler and programmer that the result of something is ignored (the result of a function call, for example)
  • In a function template, if a return type is given by a template parameter type T, and you return the result of some function call that could be different from T in some situation. An explicit cast to T could, in the void case, prevent a compile time error:
    int f() { return 0; } void g() { return (void)f(); }
  • Inhibiting the compiler to choose a comma operator overload ((void)a, b will never invoke an overloaded comma operator function).

Note that the Standard guarantees that there will never be an operator void() called if you cast a class object to void (some GCC versions ignore that rule, though).

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