decl9.c

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

// Build don't link
// Origin: [e-mail]
// Contributed by Gabriel Dos Reis <[e-mail]>

typedef struct { } S;           // OK
typedef struct { };             // ERROR - Missing type-name

typedef union { } U;            // OK
typedef union { };              // ERROR - Missing type-name