标题："time.h"
日期和时间函数
time_t和clock_t和size_t都是与long有同等意义的名字。
本类别给出时间和日期处理函数 
头文件 time.h 
函数列表 
函数类别 函数用途 详细说明 
long clock(void); 返回程序开始执行后占用的处理器时间。 
得到时间差
delay（int n）；表明延时n毫秒；
sleep（int n）；延时n秒后刷新； 
double difftime(long t2,long t1) ;返回t2-t1得值。
long mktime (struct tm*);将结构体中的当地时间转换为日历时间。
得到时间 
long time (long *tp);返回当前日历时间，同时将返回值赋给*tp;
时间转换函数 得到以ASCII码表示的时间 char *asctime (const struct tm *tp);
得到字符串表示的时间 char *ctime(const time_t *tp); 
得到指定格式的时间 size_t strftime(char *s,size_t smax,const char *fmt,const struct tm *tp);
time.h的原文件为
/* 
* time.h
* This file has no copyright assigned and is placed in the Public Domain.
* This file is a part of the mingw-runtime package.
* No warranty is given; refer to the file DISCLAIMER within the package.
*
* Date and time functions and types.
*
*/
#ifndef        _TIME_H_
#define        _TIME_H_
/* All the headers include this file. */
#include <_mingw.h>
#define __need_wchar_t
#define __need_size_t
#define __need_NULL
#ifndef RC_INVOKED
#include <stddef.h>
#endif        /* Not RC_INVOKED */
/*
* Number of clock ticks per second. A clock tick is the unit by which
* processor time is measured and is returned by 'clock'.
*/
#define        CLOCKS_PER_SEC        ((clock_t)1000)
#define        CLK_TCK                CLOCKS_PER_SEC
#ifndef RC_INVOKED
/*
* A type for storing the current time and date. This is the number of
* seconds since midnight Jan 1, 1970.
* NOTE: This is also defined in non-ISO sys/types.h.
*/
#ifndef _TIME_T_DEFINED
typedef        long        time_t;
#define _TIME_T_DEFINED
#endif
#ifndef __STRICT_ANSI__
/* A 64-bit time_t to get to Y3K */
#ifndef _TIME64_T_DEFINED
typedef __int64 __time64_t;
#define _TIME64_T_DEFINED
#endif
#endif
/*
* A type for measuring processor time (in clock ticks).
*/
#ifndef _CLOCK_T_DEFINED
typedef        long        clock_t;
#define _CLOCK_T_DEFINED
#endif
#ifndef _TM_DEFINED
/*
* A structure for storing all kinds of useful information about the
* current (or another) time.
*/
struct tm
{
int        tm_sec;                /* Seconds: 0-59 (K&R says 0-61?) */
int        tm_min;                /* Minutes: 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 Jan. 1: 0-365 */
int        tm_isdst;        /* +1 Daylight Savings Time, 0 No DST,
* -1 don't know */
};
#define _TM_DEFINED
#endif
#ifdef        __cplusplus
extern "C" {
#endif
_CRTIMP clock_t __cdecl        clock (void);
_CRTIMP time_t __cdecl        time (time_t*);
_CRTIMP double __cdecl        difftime (time_t, time_t);
_CRTIMP time_t __cdecl        mktime (struct tm*);
/*
* These functions write to and return pointers to static buffers that may
* be overwritten by other function calls. Yikes!
*
* NOTE: localtime, and perhaps the others of the four functions grouped
* below may return NULL if their argument is not 'acceptable'. Also note
* that calling asctime with a NULL pointer will produce an Invalid Page
* Fault and crap out your program. Guess how I know. Hint: stat called on
* a directory gives 'invalid' times in st_atime etc...
*/
_CRTIMP char* __cdecl                asctime (const struct tm*);
_CRTIMP char* __cdecl                ctime (const time_t*);
_CRTIMP struct tm*  __cdecl        gmtime (const time_t*);
_CRTIMP struct tm*  __cdecl        localtime (const time_t*);
_CRTIMP size_t __cdecl                strftime (char*, size_t, const char*, const struct tm*);
#ifndef __STRICT_ANSI__
extern _CRTIMP void __cdecl        _tzset (void);
#ifndef _NO_OLDNAMES
extern _CRTIMP void __cdecl        tzset (void);
#endif
_CRTIMP char* __cdecl        _strdate(char*);
_CRTIMP char* __cdecl        _strtime(char*);
/* These require newer versions of msvcrt.dll (6.10 or higher). */ 
#if __MSVCRT_VERSION__ >= 0x0601
_CRTIMP __time64_t __cdecl  _time64( __time64_t);
_CRTIMP __time64_t __cdecl  _mktime64 (struct tm*);
_CRTIMP char* __cdecl _ctime64 (const __time64_t*);
_CRTIMP struct tm*  __cdecl _gmtime64 (const __time64_t*);
_CRTIMP struct tm*  __cdecl _localtime64 (const __time64_t*);
#endif /* __MSVCRT_VERSION__ >= 0x0601 */
/*
* _daylight: non zero if daylight savings time is used.
* _timezone: difference in seconds between GMT and local time.
* _tzname: standard/daylight savings time zone names (an array with two
*          elements).
*/
#ifdef __MSVCRT__
/* These are for compatibility with pre-VC 5.0 suppied MSVCRT. */
extern _CRTIMP int* __cdecl        __p__daylight (void);
extern _CRTIMP long* __cdecl        __p__timezone (void);
extern _CRTIMP char** __cdecl        __p__tzname (void);
__MINGW_IMPORT int        _daylight;
__MINGW_IMPORT long        _timezone;
__MINGW_IMPORT char         *_tzname[2];
#else /* not __MSVCRT (ie. crtdll) */
#ifndef __DECLSPEC_SUPPORTED
extern int*        _imp___daylight_dll;
extern long*        _imp___timezone_dll;
extern char**        _imp___tzname;
#define _daylight        (*_imp___daylight_dll)
#define _timezone        (*_imp___timezone_dll)
#define _tzname                (*_imp___tzname)
#else /* __DECLSPEC_SUPPORTED */
__MINGW_IMPORT int        _daylight_dll;
__MINGW_IMPORT long        _timezone_dll;
__MINGW_IMPORT char*        _tzname[2];
#define _daylight        _daylight_dll
#define _timezone        _timezone_dll
#endif /* __DECLSPEC_SUPPORTED */
#endif /* not __MSVCRT__ */
#ifndef _NO_OLDNAMES
#ifdef __MSVCRT__
/* These go in the oldnames import library for MSVCRT. */
__MINGW_IMPORT int        daylight;
__MINGW_IMPORT long        timezone;
__MINGW_IMPORT char         *tzname[2];
#else /* not __MSVCRT__ */
/* CRTDLL is royally messed up when it comes to these macros.
TODO: import and alias these via oldnames import library instead 
of macros.  */
#define daylight        _daylight
/* NOTE: timezone not defined because it would conflict with sys/timeb.h.
Also, tzname used to a be macro, but now it's in moldname. */
__MINGW_IMPORT char         *tzname[2];
#endif /* not __MSVCRT__ */
#endif        /* Not _NO_OLDNAMES */
#endif        /* Not __STRICT_ANSI__ */
#ifndef _WTIME_DEFINED
/* wide function prototypes, also declared in wchar.h */
#ifndef __STRICT_ANSI__
#ifdef __MSVCRT__
_CRTIMP wchar_t* __cdecl        _wasctime(const struct tm*);
_CRTIMP wchar_t* __cdecl        _wctime(const time_t*);
_CRTIMP wchar_t* __cdecl        _wstrdate(wchar_t*);
_CRTIMP wchar_t* __cdecl        _wstrtime(wchar_t*);
#if __MSVCRT_VERSION__ >= 0x0601
_CRTIMP wchar_t* __cdecl        _wctime64 (const __time64_t*);
#endif
#endif /*  __MSVCRT__ */
#endif /* __STRICT_ANSI__ */
_CRTIMP size_t __cdecl                wcsftime (wchar_t*, size_t, const wchar_t*, const struct tm*);
#define _WTIME_DEFINED
#endif /* _WTIME_DEFINED */ 
#ifdef        __cplusplus
}
#endif
#endif        /* Not RC_INVOKED */
#endif        /* Not _TIME_H_ */