C ++空数组大小

Question

I initialized an array in three different ways (either on heap or on stack), but contrary to my expectation, there appears to be two different values for their size. I don't understand why.

int asd[0];    
sizeof(asd);   //ouput 0;   

int asd={};
sizeof(asd);    //output 4;

int *asd=new int[0];
sizeof(asd);    //output 4;

Since an array name is a pointer to an allocated memory block and as the size of a pointer is 4, I consider that outputs 2 and 3 are correct.

But what I don't understand is why the output 1 is not showing size 4.

Answer 1

The last two of your examples are not arrays;

The first is: int asd[0] is defining an array of size 0, which is not allowed.

If the expression is a constant expression, it shall have a value greater than zero.

The second: int asd={}; is int using aggregate initializaion. The size of int 4 bytes.

The third: int *asd=new int[0]; is a pointer of type int pointing to a dynamically allocated memory. The size of the pointer is 4 bytes (2^32 addresses).