How to deallocate 3D arrays (array of pointers to arrays)

[KM]

I allocated memory within an DLL using malloc:

I = (float **)malloc(zmax * sizeof(float *)); 

	for( i = 0; i <= zmax; ++i) 
	{
     	I[i] = (float *)malloc(xmax*ymax * sizeof(float));
	}

I deallocated using free:

for( i = 1; i <= zmax; ++i) 
	{
     	free(I[i]);
	}
	free(I);
	free(*I);

When I call this DLL from Labview multiple times the program is running out of memory. I want to make sure that this behavior is not due to wrong deallocation inside the DLL.
Can anyone help me?
Thanks in advance.

[_matze]

You allocate using this loop with i set to 0:

for( i = 0; i <= zmax; ++i) 
{
	I[i] = (float *)malloc(xmax*ymax * sizeof(float));
}

But you deallocate with i set to 1:

for( i = 1; i <= zmax; ++i) 
{
	free(I[i]);
}

This looks wrong to me. I guess this is the fault. Just set i to 0 and check the result.

Besides, why do you note an additional free?

free(*I);

I think this is not necessary.

[the third dim himself]

I = (float **)malloc(zmax * sizeof(float *));

this is not three d