size of array passed to C++ function? [duplicate]

Question

Possible Duplicate:
determine size of array if passed to function

How can I get the size of a C++ array that is passed to a function?

In the following code, the sizeof(p_vertData) does not return the correct size of the array.

float verts[] = {
 -1.0,1.0,1.0,
 1.0,1.0,1.0,
 1.0,-1.0,1.0,
 -1.0,-1.0,1.0,

 -1.0,1.0,-1.0,
 1.0,1.0,-1.0,
 1.0,-1.0,-1.0,
 -1.0,-1.0,-1.0
};

void makeVectorData(float p_vertData[]) {   
 int num = (sizeof(p_vertData)/sizeof(int)); 
 cout << "output: " << num << endl;
}; 

What am I doing wrong?

Answer 1

You can't - arrays decay to pointers when passed as function parameters so sizeof is not going to help you.

Answer 2

If you don't mind templates, you can do as follows. Note that it will work only if the array size is known at compile time.

template <int N>
void makeVectorData(float (&p_vertData)[N]) {   
 int num = (sizeof(p_vertData)/sizeof(p_verData[0])); 
 cout << "output: " << num << endl;
};

Beware also that you should divide sizeof(array) by an array element size. In your example, you're dividing the size of an array of float by the size of an integer.