Richard Heathfield said:
Anonymous structures, though, are a syntax error, and a diagnostic is
required.
You can fake them, though, if you have sufficiently poor taste.
For example, a quick grep in my system's implementation headers
found this abortion:
typedef struct siginfo {
int si_signo;
int si_errno;
int si_code;
union {
int _pad[SI_PAD_SIZE];
/* kill() */
struct {
pid_t _pid; /* sender's pid */
__ARCH_SI_UID_T _uid; /* sender's uid */
} _kill;
/* POSIX.1b timers */
struct {
timer_t _tid; /* timer id */
int _overrun; /* overrun count */
char _pad[sizeof( __ARCH_SI_UID_T) - sizeof(int)];
sigval_t _sigval; /* same as below */
int _sys_private; /* not to be passed to user */
} _timer;
/* POSIX.1b signals */
struct {
pid_t _pid; /* sender's pid */
__ARCH_SI_UID_T _uid; /* sender's uid */
sigval_t _sigval;
} _rt;
/* SIGCHLD */
struct {
pid_t _pid; /* which child */
__ARCH_SI_UID_T _uid; /* sender's uid */
int _status; /* exit code */
clock_t _utime;
clock_t _stime;
} _sigchld;
/* SIGILL, SIGFPE, SIGSEGV, SIGBUS */
struct {
void __user *_addr; /* faulting insn/memory ref. */
#ifdef __ARCH_SI_TRAPNO
int _trapno; /* TRAP # which caused the signal */
#endif
} _sigfault;
/* SIGPOLL */
struct {
__ARCH_SI_BAND_T _band; /* POLL_IN, POLL_OUT, POLL_MSG *
/
int _fd;
} _sigpoll;
} _sifields;
} siginfo_t;
#endif
/*
* How these fields are to be accessed.
*/
#define si_pid _sifields._kill._pid
#define si_uid _sifields._kill._uid
#define si_tid _sifields._timer._tid
#define si_overrun _sifields._timer._overrun
#define si_sys_private _sifields._timer._sys_private
#define si_status _sifields._sigchld._status
#define si_utime _sifields._sigchld._utime
#define si_stime _sifields._sigchld._stime
#define si_value _sifields._rt._sigval
#define si_int _sifields._rt._sigval.sival_int
#define si_ptr _sifields._rt._sigval.sival_ptr
#define si_addr _sifields._sigfault._addr
#ifdef __ARCH_SI_TRAPNO
#define si_trapno _sifields._sigfault._trapno
#endif
#define si_band _sifields._sigpoll._band
#define si_fd _sifields._sigpoll._fd
On Unix-like systems you can probably find several like this
using a command similar to this, which is what I used:
grep '#define[[:space:]]\+[a-z]\+_[^.]*\.' /usr/include -r