What is the size of void?

Question

What would this statement yield?

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

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Edit: An extension to the question.

If sizeof(void) yields 1 in GCC compiler, then 1 byte of memory is allocated and the pointer p points to that byte and would p++ be incremented to 0x2346? Suppose p was 0x2345. I am talking about p and not *p.

Answer 1

void has no size, that would be a compilation error. For the same reason you can't do something like:

void n;

EDIT. To my surprise, doing sizeof(void) actually does compile in C:

$ echo 'int main() { printf("%d", sizeof(void)); }' | gcc -xc -w - && ./a.out 
1

However, in C++ it does not:

$ echo 'int main() { printf("%d", sizeof(void)); }' | gcc -xc++ -w - && ./a.out 
<stdin>: In function 'int main()':
<stdin>:1: error: invalid application of 'sizeof' to a void type
<stdin>:1: error: 'printf' was not declared in this scope

Answer 2

In C, sizeof(void) == 1 in GCC, but this appears to depend on your compiler.

In C++, I get:

In function 'int main()':
Line 2: error: invalid application of 'sizeof' to a void type
compilation terminated due to -Wfatal-errors.

Answer 3

Although void may stand in place for a type, it cannot actually hold a value. Therefore, it has no size in memory. Getting the size of a void isn’t defined.

A void pointer is simply a language construct meaning a pointer to untyped memory.

Answer 4

sizeof() cannot be applied to incomplete types. And void is incomplete type that cannot be completed.

Answer 5

If you are using GCC and you are not using compilation flags that remove compiler specific extensions, then sizeof(void) is 1. GCC has a nonstandard extension that does that.

In general, void is a incomplete type, and you cannot use sizeof for incomplete types.

Answer 6

Taking the size of void is a GCC extension.

Answer 7

To the 2nd part of the question: Note that sizeof(void *)!= sizeof(void). On a 32-bit arch, sizeof(void *) is 4 bytes, so p++, would be set accordingly.The amount by which a pointer is incremented is dependent on the data it is pointing to. So, it will be increased by 1 byte.