C编程中数组中的星号

Question

What is the difference between sizeof(arr) and sizeof(*arr) in C.

int arr[] = { 1, 2, 0, 5, 5 };
int n = sizeof( arr ) / sizeof( *arr );

Answer 1

sizeof(arr) is the size of the entire array. In your case, it is the size of 5 integers. In case int is 4 bytes it is 5 * 4 = 20.

*arr is the first element of the array. It is equal to arr[0] . sizeof(*arr) is the size of this element. In your case it is 4 bytes.

So sizeof( arr ) / sizeof( *arr ); will give the number of elements in the array.

You should note that this will only work in the scope where the array is defined. If you are passing the array to a function, the arr will decay into a pointer and sizeof (arr) will only give you the size of a pointer in your system (typically 4 or 8 bytes).