Proposal: API for thread-safe time zone functions

Clive D.W. Feather clive at
Fri Jun 8 15:10:59 UTC 2001

Garrett Wollman said:
>>     struct timezone;                      // Opaque structure
>>     typedef struct timezone timezone_t;   // Opaque typedef
> Not at all.  That typedef is not opaque, it is entirely transparent,
> and simply resolves to an incomplete structure.  Consider the
> following two-line compilation unit:
> struct timezone *foo;		// Compiles fine...
> timezone_t foo;			// Syntax error!

Not a syntax error, a declaration error. Try:

clive at finch-staff-1> cat xx.c
struct timezone;
typedef struct timezone timezone_t;

struct timezone s;
struct timezone *sp;
extern struct timezone es;
extern struct timezone *esp;
timezone_t t;
timezone_t *tp;
extern timezone_t et;
extern timezone_t *etp;
clive at finch-staff-1> cc xx.c
xx.c:4: storage size of `s' isn't known
xx.c:8: storage size of `t' isn't known
clive at finch-staff-1>

Nothing to do with typedef or not, just to do with the rules for

>> You *are* using public and private headers, aren't you ? That is, users
>> of your library include <timezone.h>
> No, users of my library include <foo.h>.  It defines some interfaces
> which take a timezone parameter.

So in foo.h write the one line:

    typedef struct timezone timezone_t;

End of story.

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