About the format type specifiers

[姚伟斌]

Thanks for your great explanation.  Explicit casts should be good for us.

2012/7/24 Maxim Dounin <mdounin at mdounin.ru>:
> Hello!
>
> On Tue, Jul 24, 2012 at 03:34:39PM +0800, 姚伟斌 wrote:
>
>> 1. The type of 'ngx_msec_int_t', from the source code, It's defined like this:
>>
>> typedef ngx_int_t   ngx_rbtree_key_int_t;
>> typedef ngx_rbtree_key_int_t  ngx_msec_int_t;
>>
>> So It should be an ngx_int_t.
>>
>> In the file of ngx_http_log_module.c, It appears like this:
>>
>> static u_char *
>> ngx_http_log_request_time(ngx_http_request_t *r, u_char *buf,
>>     ngx_http_log_op_t *op)
>> {
>>     ngx_time_t      *tp;
>>     ngx_msec_int_t   ms;
>>
>>     tp = ngx_timeofday();
>>
>>     ms = (ngx_msec_int_t)
>>              ((tp->sec - r->start_sec) * 1000 + (tp->msec - r->start_msec));
>>     ms = ngx_max(ms, 0);
>>
>>     return ngx_sprintf(buf, "%T.%03M", ms / 1000, ms % 1000);
>> }
>
> In case of ngx_msec_int_t it's almost always possible to use %M
> which has identical size, as it's only used for intermediate
> computations and ensured to be non-negative.  (Note the
> ngx_max(ms, 0) call in the code above.)
>
>> 2. The type of '' ngx_gid_t" and "ngx_uid_t", from the source code.
>> They are defined like this:
>>
>>  typedef uid_t  ngx_uid_t;
>>  typedef gid_t  ngx_gid_t;
>>
>> And I googled [1][2] about the types of uid_t and gid_t and They seem
>> to unsigned integer.
>
> Just a side note: no, POSIX doesn't define signedness of
> uid_t/gid_t.  It only says they should be "integer types", see
> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_types.h.html.
>
>>
>> In the file of ngx_process_cycle.c, it appears like this:
>>
>>     if (geteuid() == 0) {
>>         if (setgid(ccf->group) == -1) {
>>             ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
>>                           "setgid(%d) failed", ccf->group);
>>             /* fatal */
>>             exit(2);
>>         }
>>
>>         if (initgroups(ccf->username, ccf->group) == -1) {
>>             ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
>>                           "initgroups(%s, %d) failed",
>>                           ccf->username, ccf->group);
>>         }
>>
>>         if (setuid(ccf->user) == -1) {
>>             ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
>>                           "setuid(%d) failed", ccf->user);
>>             /* fatal */
>>             exit(2);
>>         }
>>     }
>>
>> I want to know the correct format specifiers with ngx_msec_int_t,
>> uid_t and gid_t. I'm a little confused with above codes.
>
> See above for ngx_msec_int_t.  Most safe way to print
> ngx_uint_t/ngx_gid_t is probably to do so with intermediate cast
> to some defined big-enough type.
>
> Strictly speaking the above code isn't correct and might print
> garbage on some platforms.  It probably worth adding explicit
> casts to int.
>
> Maxim Dounin
>
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