__EXPORT int px4_simple_app_main(int argc, char *argv[]);__EXPORT can be found in visibility.h
#ifdef __EXPORT
# undef __EXPORT
#endif
#define __EXPORT __attribute__ ((visibility ("default")))
"The keyword __attribute__ allows you to specify special attributes when making a declaration. This keyword is followed by an attribute specification inside double parentheses. "
int sensor_sub_fd = orb_subscribe(ORB_ID(sensor_combined));
sensor_combined is a structure, containing "Sensor readings in raw and SI-unit form";
ORB_ID Generates a pointer to the uORB metadata structure for a given topic. The topic must have been declared previously in scope with ORB_DECLARE().
