user-0 提问: linux下settimeofday函数调用失败，何故？

回复:
user: user-0
content: 谢谢各位，我自己 已经找到问题了。  写出来 供 像我这样的初学者 参考：  是struct   timeval  结构中 time_t    的值为负导致的。  在struct   tm 结构中的tm_year必须超过1970年，否则为负数。因为linux是以1970年起计算秒数计时。早于这个时间，就导致是负数，报错了。 （在32位系统，这个数也不能超过2038年。）

user: user-1
content: 检查下errno。

user: user-2
content: GETTIMEOFDAY Section: Linux Programmer's Manual (2) Updated: 2004-05-27  --------------------------------------------------------------------------------    NAME gettimeofday, settimeofday - get / set time    SYNOPSIS #include <sys/time.h>  int gettimeofday(struct timeval *tv, struct timezone *tz);  int settimeofday(const struct timeval *tv , const struct timezone *tz);     DESCRIPTION The functions gettimeofday and settimeofday can get and set the time as well as a timezone. The tv argument is a timeval struct, as specified in <sys/time.h>:   struct timeval { time_t          tv_sec;         /* seconds */ suseconds_t     tv_usec;        /* microseconds */ };  and gives the number of seconds and microseconds since the Epoch (see time(2)). The tz argument is a timezone :    struct timezone { int     tz_minuteswest; /* minutes W of Greenwich */ int     tz_dsttime;     /* type of dst correction */ };  The use of the timezone struct is obsolete; the tz_dsttime field has never been used under Linux - it has not been and will not be supported by libc or glibc. Each and every occurrence of this field in the kernel source (other than the declaration) is a bug. Thus, the following is purely of historic interest.   The field tz_dsttime contains a symbolic constant (values are given below) that indicates in which part of the year Daylight Saving Time is in force. (Note: its value is constant throughout the year - it does not indicate that DST is in force, it just selects an algorithm.) The daylight saving time algorithms defined are as follows :   DST_NONE     /* not on dst */  DST_USA     /* USA style dst */  DST_AUST    /* Australian style dst */  DST_WET     /* Western European dst */  DST_MET     /* Middle European dst */  DST_EET     /* Eastern European dst */  DST_CAN     /* Canada */  DST_GB      /* Great Britain and Eire */  DST_RUM     /* Rumania */  DST_TUR     /* Turkey */  DST_AUSTALT /* Australian style with shift in 1986 */   Of course it turned out that the period in which Daylight Saving Time is in force cannot be given by a simple algorithm, one per country; indeed, this period is determined by unpredictable political decisions. So this method of representing time zones has been abandoned. Under Linux, in a call to settimeofday the tz_dsttime field should be zero.   Under Linux there is some peculiar `warp clock' semantics associated to the settimeofday system call if on the very first call (after booting) that has a non-NULL tz argument, the tv argument is NULL and the tz_minuteswest field is nonzero. In such a case it is assumed that the CMOS clock is on local time, and that it has to be incremented by this amount to get UTC system time. No doubt it is a bad idea to use this feature.   The following macros are defined to operate on a struct timeval :    #define       timerisset(tvp)\          ((tvp)->tv_sec || (tvp)->tv_usec) #define       timercmp(tvp, uvp, cmp)\ ((tvp)->tv_sec cmp (uvp)->tv_sec ||\ (tvp)->tv_sec == (uvp)->tv_sec &&\ (tvp)->tv_usec cmp (uvp)->tv_usec) #define       timerclear(tvp)\          ((tvp)->tv_sec = (tvp)->tv_usec = 0)  If either tv or tz is null, the corresponding structure is not set or returned.   Only the super user may use settimeofday.     RETURN VALUE gettimeofday and settimeofday return 0 for success, or -1 for failure (in which case errno is set appropriately).    ERRORS EFAULT  One of tv or tz pointed outside the accessible address space.  EINVAL  Timezone (or something else) is invalid.  EPERM  The calling process has insufficient privilege to call settimeofday; under Linux the CAP_SYS_TIME capability is required.     NOTE The prototype for settimeofday and the defines for timercmp, timerisset, timerclear, timeradd, timersub are (since glibc2.2.2) only available if _BSD_SOURCE is defined (either explicitly, or implicitly, by not defining _POSIX_SOURCE or compiling with the -ansi flag).  Traditionally, the fields of struct timeval were longs.     CONFORMING TO SVr4, BSD 4.3. POSIX 1003.1-2001 describes gettimeofday() but not settimeofday().    SEE ALSO date(1), adjtimex(2), time(2), ctime(3), ftime(3), capabilities(7)  --------------------------------------------------------------------------------

user: user-3
content: 单步调试看看 t_timet和rec的值。