how we structure C type definitions

foo.c

// enumerations cannot be forward-declared
// the compiler needs to see its definition
// if it wants to choose an underlying type other than int
// therefore, we start with enum definitions
enum foo
{
  FOO,
  BAR
};

// the enum typedef could be joined with the definition
// we list it seperately for consistency
typedef enum foo foo;

// forward-declarations of structs and unions
// same as with enums, using the same name is perfectly fine
// if you want to use different names, don't use preceding underscores
// trailing ones are fine, but why bother?
typedef struct bar bar;
typedef union baz baz;

// actual definitions of struct and union types
struct bar
{
  int a;
  int b;
};

union baz
{
  int i;
  float f;
};