void

Keyword

Empty data type.

When used as a function return type, void means that the function does not return a value. For example,

void hello (char *name)
{
  printf("Hello, %s.", name);
}

When found in a function heading, void means the function does not take any parameters. For example,

int init (void)
{
  return 1;
}

This is not the same as defining

int init ()
{
  return 1;
}

because in the second case the compiler will not check whether the function is really called with no arguments at all; instead, a function call with arbitrary number of arguments will be accepted without any warnings (this is implemented only for the compatibility with the old-style function definition syntax).

Pointers can also be declared as void. They can't be dereferenced without explicit casting. This is because the compiler can't determine the size of the object the pointer points to. For example,

int x;
float f;
void *p = &x;    // p points to x
*(int*)p = 2;
p = &r;          // p points to r
*(float*)p = 1.1;