2.2 — Void

Void is the easiest of the data types to explain. Basically, it means “no type”!

Consequentially, variables can not be defined with a type of void:

1	void value; // won't work, variables can't be defined with a void type

Void is typically used in several different contexts:

1) Most commonly, as a way to indicate that a function does not return a value:

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void writeValue(int x) // void here means no return value {     std::cout << "The value of x is: " << x << std::endl;     // no return statement, because the return type is void }

2) In C, as a way to indicate that a function does not take any parameters:

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int getValue(void) // void here means no parameters {     int x;     std::cin >> x;     return x; }

The explicit use of keyword void to mean “no parameters” is a holdover from C, and is not required in C++. The following code is equivalent, and preferred in C++:

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int getValue() // empty function parameters is an implicit void {     int x;     std::cin >> x;     return x; }

Rule: Use an empty parameter list instead of void to indicate no function parameters are expected

3) The void keyword has a third (more advanced) use in C++ that we cover in section 6.13 -- Void pointers. Since we haven’t covered what a pointer is yet, you don’t need to worry about this case for now. 🙂