What does void mean in C, C++, and C#?


Looking to get the fundamentals on where the term "void" comes from, and why it is called void. The intention of the question is to assist someone who has no C experience, and is suddenly looking at a C-based codebase.

5/28/2018 5:23:59 PM

Accepted Answer

Basically it means "nothing" or "no type"

There are 3 basic ways that void is used:

  1. Function argument: int myFunc(void) -- the function takes nothing.

  2. Function return value: void myFunc(int) -- the function returns nothing

  3. Generic data pointer: void* data -- 'data' is a pointer to data of unknown type, and cannot be dereferenced

Note: the void in a function argument is optional in C++, so int myFunc() is exactly the same as int myFunc(void), and it is left out completely in C#. It is always required for a return value.

10/15/2014 3:11:10 PM

I have always taken it to mean absent. Here are four cases in the C language that matches to this use of absent

  • R f(void) - Function parameters are absent
  • void f(P) - Return value is absent
  • void *p - Type of what is pointed to is absent
  • (void) p - Usage of value is absent

Other C descendants use it for other things. The D programming language uses it for cases where an initializer is absent

  • T t = void; - initializing value is absent

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