inconsistent output of the function sizeof

beginners
#1

Hi guys!

I’m new to openframeworks, so in advance please apologize if my question is totally trivial - as it probably is.

Anyway, here’s a code snippet that’s causing me trouble:

in the h file:

  
unsigned char*	depthMatrix;

in the cpp file:

  
	depthMatrix = new unsigned char[ofGetWidth()*ofGetHeight()];  
	printf("defined size: %d, init size: %d\n", ofGetWidth()*ofGetHeight(), sizeof(depthMatrix));

and the marvellous output:

defined size: 786432, init size: 4

Does anyone know why this array gets defined to a length of 4, while I’m specifically defining it to over 700000??

Thanks in advance for any pointers!

Gavrilo

#2

Hey Gavrilo,

the sizeof function will give you the number of bytes that the type of variable that you pass in takes, *not* the size of an array. So, for instance:

sizeof(bool) = 1
sizeof(float) = 4
sizeof(int) = 4
sizeof(double) = 8
sizeof(char*) = 8 // signed or unsigned – doesn’t matter. it’s the size of a pointer

AFAIK, there is no way to get the size of an array once you have allocated it. If you absolutely need to have a way to get the size of a container and can’t save the original allocation size, use a vector.

http://www.cplusplus.com/reference/stl/vector/vector/