Where a function call has input-output arguments, the arguments must be pointers to the actual data. The size_parameter_is_pointer attribute identifies the argument that points to the number of elements in an array, relative to the array argument, and indicates that the argument is a pointer.
In the example below, the first argument points to the number of elements in the second argument.
void myfunction4(long *count, float *numbers);
The IDL representation is:
[api_to_hook] void myfunction4(
[in] long *count,
[in,size_parameter_is_pointer(-1)] float *numbers);