C ++类型转换：错误C2440：'='：无法从'short *'转换为'DCTBLOCK'

Question

I have this types:

typedef short DCTELEM;
typedef DCTELEM DCTBLOCK[64];

Array of last type and a pointer to a malloc'ed array of shorts:

DCTBLOCK MQUAD;
short * ptrArray;

I need MQUAD to bet to specific location pointed to by ptrArray;

In CI would prolly write something like

MQUAD = ptrArray + 3 * 2;

and have MQUAD after that pointing to a needed location, but I get

error C2440: '=' : cannot convert from 'short *' to 'DCTBLOCK'

in c++, cause I know there is a difference in a type of array and a pointer to some-type.

Answer 1

Your MQUAD variable is an array, not a pointer, so you can't assign to it (thanks to Remy Lebeau's comment). If you declare it as:

DCTELEM *MQUAD;

then you can assign to it:

MQUAD = reinterpret_cast<DCTELEM *>(ptrArray + 3 * 2); 

This is using the C++ cast syntax. You can use C cast syntax if you like too.

Answer 2

The main mistake is

DCTBLOCK MQUAD // it's wrong
DCTELEM* MQUAD // it's right

and you may cast as u want

MQUAD = ptrArray + 3 * 2;