[Swan-dev] IRC: fields of timeval

D. Hugh Redelmeier hugh at mimosa.com
Thu Sep 6 05:00:37 UTC 2018

<cagney> DHR, fyi, 6d0aea9400 isn't portable
<cagney> the timeval fields are long long on 32-bit machines

Thanks.  You are right about the tv_sec field.

I happened to look at select(2) when I wrote 6d0aea9400.  It says that the 
fields are long.  Nothing about long long on 32-bit machines.

It turns out that that man page is wrong.  gettimeofday(2) says

           struct timeval {
               time_t      tv_sec;     /* seconds */
               suseconds_t tv_usec;    /* microseconds */

and in the notes:

       Traditionally, the fields of struct timeval were of type long.

There is no reason for tv_usec to be anything other than long, int32_t, 
unsigned long, or uint_32: it needs to represent 0 - 999999.  Is it legal 
for tv_usec to have other values?

time_t is a very natural type for seconds.  And we're going to get into 
trouble if it stays at 32 bits.  So int64_t is a good choice.  long is 

time_t is signed.  If tv_sec is negative, can/should tv_usec be negative?

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