The type 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 GNU 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
原答案来源于Stack Overflow https://stackoverflow.com/questions/1666224/what-is-the-size-of-void