time_t tm timeval 和 时间字符串的转换方法

struct tm { 
    int tm_sec;   /* seconds after the minute - [0,59] */ 
    int tm_min;   /* minutes after the hour - [0,59] */ 
    int tm_hour;  /* hours since midnight - [0,23] */ 
    int tm_mday;  /* day of the month - [1,31] */ 
    int tm_mon;   /* months since January - [0,11] */ 
    int tm_year;  /* years since 1900 */ 
    int tm_wday;  /* days since Sunday - [0,6] */ 
    int tm_yday;  /* days since January 1 - [0,365] */ 
    int tm_isdst;  /* daylight savings time flag */ 
    }; 

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

time_t time(time_t *t); //取得从1970年1月1日至今的秒数 
char *asctime(const struct tm *tm); //将结构中的信息转换为真实世界的时间，以字符串的形式显示 
char *ctime(const time_t *timep); //将timep转换为真是世界的时间，以字符串显示，它和asctime不同就在于传入的参数形式不一样 
struct tm *gmtime(const time_t *timep); //将time_t表示的时间转换为没有经过时区转换的UTC时间，是一个struct tm结构指针  
struct tm *localtime(const time_t *timep); //和gmtime类似，但是它是经过时区转换的时间。 
time_t mktime(struct tm *tm); //将struct tm 结构的时间转换为从1970年至今的秒数 
int gettimeofday(struct timeval *tv, struct timezone *tz); //返回当前距离1970年的秒数和微妙数，后面的tz是时区，一般不用 
double difftime(time_t time1, time_t time2); //返回两个时间相差的秒数 

time_t t; //秒时间 
tm* local; //本地时间  
tm* gmt;  //格林威治时间 
char buf[128]= {0}; 
 
t = time(NULL); //或者time(&t);//获取目前秒时间 
local = localtime(&t); //转为本地时间 
strftime(buf, 64, "%Y-%m-%d %H:%M:%S", local); 
std::cout << buf << std::endl; 
 
gmt = gmtime(&t);//转为格林威治时间 
strftime(buf, 64, "%Y-%m-%d %H:%M:%S", gmt); 
std::cout << buf << std::endl; 

 
tm tm_; 
time_t t_; 
char buf[128]= {0}; 
 
strcpy(buf, "2012-01-01 14:00:00"); 
strptime(buf, "%Y-%m-%d %H:%M:%S", &tm_); //将字符串转换为tm时间 
tm_.tm_isdst = -1; 
t_ = mktime(&tm_); //将tm时间转换为秒时间 
t_ += 3600; //秒数加3600 
 
tm_ = *localtime(&t_);//输出时间 
strftime(buf, 64, "%Y-%m-%d %H:%M:%S", &tm_); 
std::cout << buf << std::endl; 
 

time_t StringToDatetime(char *str) 
{ 
  tm tm_; 
  int year, month, day, hour, minute,second; 
  sscanf(str,"%d-%d-%d %d:%d:%d", &year, &month, &day, &hour, &minute, &second); 
  tm_.tm_year = year-1900; 
  tm_.tm_mon  = month-1; 
  tm_.tm_mday = day; 
  tm_.tm_hour = hour; 
  tm_.tm_min  = minute; 
  tm_.tm_sec  = second; 
  tm_.tm_isdst = 0; 
 
  time_t t_ = mktime(&tm_); //已经减了8个时区 
  return t_; //秒时间 
} 

struct timeval start_time, over_time, consume_time;
gettimeofday(&over_time, NULL);//get the current time
start_time = over_time;
 do something.....
gettimeofday(&over_time, NULL);
timeval_subtract(&consume_time, &start_time, &over_time);//计算时间差104./** 
   * 计算两个时间的间隔，得到时间差 
   * @param struct timeval* resule 返回计算出来的时间 
   * @param struct timeval* x 需要计算的前一个时间 
   * @param struct timeval* y 需要计算的后一个时间 
   * return -1 failure ,0 success 
 **/ 
timeval_subtract(struct timeval* result, struct timeval* x, struct timeval* y) 
 { 
    if ( x->tv_sec>y->tv_sec ) 
         return -1; 
  
    if ( (x->tv_sec==y->tv_sec) && (x->tv_usec>y->tv_usec) ) 
         return -1; 
  
    result->tv_sec = ( y->tv_sec-x->tv_sec ); 
    result->tv_usec = ( y->tv_usec-x->tv_usec ); 
  
    if (result->tv_usec<0) 
    { 
         result->tv_sec--; 
         result->tv_usec+=1000000; 
    } 
  
    return 0; 
 }