I hope you are looking for this ITK function.
SA_API int SA_ask_roles_from_group ( tag_t group_tag,
int * num_of_roles,
tag_t ** role_tags
Allocates an array of tags and stores in the array all roles of the specified group. role_tags points to the array of tags. num_of_roles stores the size of the array. The client is responsible for deallocating the array of role_tags. Use MEM_free to free the memory pointed to by role_tags.
role_tags (OF) num_of_roles