Arduino pass by reference

arduino_code.c

typedef struct
{
  int data;
}st_struct;

void my_fn(st_struct *st)
{
  ...
}

void setup()
{
  ...
}

void loop()
{
  ...
}

arduino_code2.c

#include "Arduino.h"
void my_fn(st_struct *st);
void setup();
void loop();
#line 1
typedef struct
{
  int data;
}st_struct;


void my_fn(st_struct *st) 
{
  ...
}

void setup() 
{
  ...
}

void loop()
{
  ...
}