Linux獲取系統時間，精確到毫秒

string GetDateTime()
{
    char strTime[30];
    struct timeval tv;
    struct timezone tz;
    struct tm *t;

    gettimeofday(&tv, &tz);
    t = localtime(&tv.tv_sec);
    snprintf(strTime, 30, "%04d%02d%02d_%02d%02d%02d.%03d",
             1900+t->tm_year, 1+t->tm_mon, t->tm_mday,
             t->tm_hour, t->tm_min, t->tm_sec, tv.tv_usec / 1000);

    return string(strTime);
}