How can I get the size of an array in C / Objective-C?

Question

I have this array:

unsigned char* data = CGBitmapContextGetData(cgctx);

then I tried to get the size with sizeof(data), but that will return me a nonsense-value of 4. data holds a big amount of information. That can't be just 4 ;)

I even get information at data[8293] ... so ... not 4 elements at all.

Answer 1

The value of 4 is not nonsense, it's the size of the pointer you asked for. There is no way in C of finding out then size of the array that a pointer points to.

Answer 2

You're confusing a pointer and the object it points to.

Answer 3

sizeof returns 4 because your variable is declared as a pointer, as opposed to a C array (char data[1024]).

To get the size you need to use CGBitmapContextGetHeight and CGBitmapContextGetWidth.

Answer 4

You're taking the size of the pointer, not of the array. Using sizeof() for arrays only work if you actually have an array to measure ;)

Answer 5

Try to use

CGBitmapContextGetBitsPerPixel
CGBitmapContextGetHeight
CGBitmapContextGetWidth

or

CGBitmapContextGetBytesPerRow
CGBitmapContextGetHeight