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

2012/7/24 Maxim Dounin <mdounin@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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