You can create a pointer with a type but no storage definition. // foo_t is opaque typedef struct foo_s foo_t; // function defined taking an opaque p

You can create a pointer with a type but no storage definition. // foo_t is opaque typedef struct foo_s foo_t; // function defined taking an opaque pointer int Baz(foo_t *f); // actual definition typedef struct foo_s { int bar; } foo_t; // function def int Baz(foo_t *f) { return f->bar; }