900214_01.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

// g++ 1.36.1 bug 900214_01

// g++ allows function members of incomplete types to be declared to be
// friends of other types.

// Cfront 2.0 passes this test.

// keywords: friends, incomplete types, function members

struct A;                       // ERROR - forward declaration

struct B {
  friend void A::foo();		// ERROR - type A is incomplete
};

void A::foo();			/* ERROR - also illegal */

struct A {
  void foo() {}
};

int main () { return 0; }