Cannot understand the following codes


I got problems on understanding the attached codes. It seems a 3rd
party API library is called.

Question1: Why assign NULL to GO_FUNCS?

Question2: GO_FUNCS looks like a struture of functions. Is there a
term for it?

Question 3: I cannot understand this line in total.
(*(void (*)
(int,t_go_measurements[]))(stGOFuncs.p_go_Measurements))(i_,ast_);

Why parenthesize an integer and a structure together?
What is possibly the type of stGOFuncs.p_go_Measurements? I did not see
its definition.
Why put void (*) ahead of the line?

I know these questions might seem silly to you, but please help. I also
want to get some links for this type of programming.


////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#include "goapi.hpp"

GO_FUNCS stGOFuncs =
{NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};

void
go_Measurements(int i_, t_go_measurements ast_[])
{
(*(void (*)
(int,t_go_measurements[]))(stGOFuncs.p_go_Measurements))(i_,ast_);
}


//Find the definition of t_go_measurements in the header file
/*
* This structure holds a set of measurements
*/
typedef struct {
long lSpeed;
int iUnit;
...
double dDistance;
} t_go_measurements;

.