sizeof(struct timeval)

Big and Blue No_4 at dsl.pipex.com
Tue Mar 14 02:30:11 CET 2006


Tony Houghton wrote:
> 
> How safe would I be assuming that 
> 
>     sizeof(struct timeval) == 2 * sizeof(long)
> 
> is always true on Linux on different architectures? 

    Based on what I was looking at today (well, yesterday now), you might 
be wrong.

    I do know that the size of a struct utmp differs between a Linux 
Itanium system and a Linux x86_64 system, and I seem to recall it migh be 
related to timeval.  I could be wrong - I wasn't interested in the timeval 
part - but this part of the bits/utmp.h include file indicates the issue:


/* The ut_session and ut_tv fields must be the same size when compiled
    32- and 64-bit.  This allows data files and shared memory to be
    shared between 32- and 64-bit applications.  */
#if __WORDSIZE == 64 && defined __WORDSIZE_COMPAT32
   int32_t ut_session;           /* Session ID, used for windowing.  */
   struct
   {
     int32_t tv_sec;             /* Seconds.  */
     int32_t tv_usec;            /* Microseconds.  */
   } ut_tv;                      /* Time entry was made.  */
#else
   long int ut_session;          /* Session ID, used for windowing.  */
   struct timeval ut_tv;         /* Time entry was made.  */
#endif


-- 
              Just because I've written it doesn't mean that
                   either you or I have to believe it.



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