Question: Understanding the Undefined Size of "void"

In C programming, the keyword "void" represents an absence of type. This raises the question: what is the size of "void"?

Answer:

The type "void" has no defined size in C. It is not a valid type for objects or pointers, so attempting to use it as such would lead to a compilation error. Specifically, the statement:

void n;

is invalid because it tries to declare a variable of a void type, which is not allowed.

Extension: Allocation and Pointer Arithmetic with "void" Pointers

Although "void" has no size, it can be used as a type for pointers. However, such pointers do not point to any specific type or size of data.

The statement:

void *p = malloc(sizeof(void));

results in a compile-time error because trying to allocate memory for a "void" type is nonsensical. The function malloc requires a valid data type to allocate memory for.

In GCC, the expression sizeof(void) surprisingly evaluates to 1. While this might seem like it assigns a size to "void", it is merely an implementation detail that should not be relied upon.

Additionally, the pointer arithmetic p on a "void" pointer is undefined and should not be used. This is because the type of data pointed to by p is unknown, making it impossible to determine what incrementing the pointer would mean.