time.h头文件实现代码

/*
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */

/*
* ISO C Standard: 4.12 DATE and TIME
*/

#ifndef _TIME_H

#if (! defined __need_time_t && !defined __need_clock_t && \
! defined __need_timespec)
# define _TIME_H 1
# include

__BEGIN_DECLS

#endif

#ifdef _TIME_H
/* Get size_t and NULL from . */
# define __need_size_t
# define __need_NULL
# include

/* This defines CLOCKS_PER_SEC, which is the number of processor clock
ticks per second. */
# include

/* This is the obsolete POSIX.1-1988 name for the same constant. */
# ifdef __USE_POSIX
# ifndef CLK_TCK
# define CLK_TCK CLOCKS_PER_SEC
# endif
# endif

#endif /* included. */

#if !defined __clock_t_defined && (defined _TIME_H || defined __need_clock_t)
# define __clock_t_defined 1

# include

/* Returned by `clock'. */
typedef __clock_t clock_t;

#endif /* clock_t not defined and or need clock_t. */
#undef __need_clock_t

#if !defined __time_t_defined && (defined _TIME_H || defined __need_time_t)
# define __time_t_defined 1

# include

/* Returned by `time'. */
typedef __time_t time_t;

#endif /* time_t not defined and or need time_t. */
#undef __need_time_t

#if !defined __timespec_defined && \
((defined _TIME_H && defined __USE_POSIX199309) || defined __need_timespec)
# define __timespec_defined 1

/* POSIX.4 structure for a time value. This is like a `struct timeval' but
has nanoseconds instead of microseconds. */
struct timespec
{
long int tv_sec; /* Seconds. */
long int tv_nsec; /* Nanoseconds. */
};

#endif /* timespec not defined and or need timespec. */
#undef __need_timespec

#ifdef _TIME_H
/* Used by other time functions. */
struct tm
{
int tm_sec; /* Seconds. [0-60] (1 leap second) */
int tm_min; /* Minutes. [0-59] */
int tm_hour; /* Hours. [0-23] */
int tm_mday; /* Day. [1-31] */
int tm_mon; /* Month. [0-11] */
int tm_year; /* Year - 1900. */
int tm_wday; /* Day of week. [0-6] */
int tm_yday; /* Days in year.[0-365] */
int tm_isdst; /* DST. [-1/0/1]*/

# ifdef __USE_BSD
long int tm_gmtoff; /* Seconds east of UTC. */
__const char *tm_zone; /* Timezone abbreviation. */
# else
long int __tm_gmtoff; /* Seconds east of UTC. */
__const char *__tm_zone; /* Timezone abbreviation. */
# endif
};

/* Time used by the program so far (user time + system time).
The result / CLOCKS_PER_SECOND is program time in seconds. */
extern clock_t clock __P ((void));

/* Return the current time and put it in *TIMER if TIMER is not NULL. */
extern time_t time __P ((time_t *__timer));

/* Return the difference between TIME1 and TIME0. */
extern double difftime __P ((time_t __time1, time_t __time0))
__attribute__ ((__const__));

/* Return the `time_t' representation of TP and normalize TP. */
extern time_t mktime __P ((struct tm *__tp));

/* Format TP into S according to FORMAT.
Write no more than MAXSIZE characters and return the number
of characters written, or 0 if it would exceed MAXSIZE. */
extern size_t strftime __P ((char *__restrict __s, size_t __maxsize,
__const char *__restrict __format,
__const struct tm *__restrict __tp));

# ifdef __USE_XOPEN
/* Parse S according to FORMAT and store binary time information in TP.
The return value is a pointer to the first unparsed character in S. */
extern char *strptime __P ((__const char *__s, __const char *__fmt,
struct tm *__tp));
# endif

/* Return the `struct tm' representation of *TIMER
in Universal Coordinated Time (aka Greenwich Mean Time). */
extern struct tm *gmtime __P ((__const time_t *__timer));

/* Return the `struct tm' representation
of *TIMER in the local timezone. */
extern struct tm *localtime __P ((__const time_t *__timer));

# if defined __USE_POSIX || defined __USE_MISC
/* Return the `struct tm' representation of *TIMER in UTC,
using *TP to store the result. */
extern struct tm *__gmtime_r __P ((__const time_t *__restrict __timer,
struct tm *__restrict __tp));
extern struct tm *gmtime_r __P ((__const time_t *__restrict __timer,
struct tm *__restrict __tp));

/* Return the `struct tm' representation of *TIMER in local time,
using *TP to store the result. */
extern struct tm *localtime_r __P ((__const time_t *__restrict __timer,
struct tm *__restrict __tp));
# endif /* POSIX or misc */

/* Return a string of the form "Day Mon dd hh:mm:ss yyyy\n"
that is the representation of TP in this format. */
extern char *asctime __P ((__const struct tm *__tp));

/* Equivalent to `asctime (localtime (timer))'. */
extern char *ctime __P ((__const time_t *__timer));

# if defined __USE_POSIX || defined __USE_MISC
/* Reentrant versions of the above functions. */

/* Return in BUF a string of the form "Day Mon dd hh:mm:ss yyyy\n"
that is the representation of TP in this format. */
extern char *asctime_r __P ((__const struct tm *__restrict __tp,
char *__restrict __buf));

/* Equivalent to `asctime_r (localtime_r (timer, *TMP*), buf)'. */
extern char *ctime_r __P ((__const time_t *__restrict __timer,
char *__restrict __buf));
# endif /* POSIX or misc */

/* Defined in localtime.c. */
extern char *__tzname[2]; /* Current timezone names. */
extern int __daylight; /* If daylight-saving time is ever in use. */
extern long int __timezone; /* Seconds west of UTC. */

# ifdef __USE_POSIX
/* Same as above. */
extern char *tzname[2];

/* Set time conversion information from the TZ environment variable.
If TZ is not defined, a locale-dependent default is used. */
extern void tzset __P ((void));
# endif

# if defined __USE_SVID || defined __USE_XOPEN
extern int daylight;
extern long int timezone;
# endif

# ifdef __USE_SVID
/* Set the system time to *WHEN.
This call is restricted to the superuser. */
extern int stime __P ((__const time_t *__when));
# endif

/* Nonzero if YEAR is a leap year (every 4 years,
except every 100th isn't, and every 400th is). */
# define __isleap(year) \
((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))

# ifdef __USE_MISC
/* Miscellaneous functions many Unices inherited from the public domain
localtime package. These are included only for compatibility. */

/* Like `mktime', but for TP represents Universal Time, not local time. */
extern time_t timegm __P ((struct tm *__tp));

/* Another name for `mktime'. */
extern time_t timelocal __P ((struct tm *__tp));

/* Return the number of days in YEAR. */
extern int dysize __P ((int __year));
# endif

# ifdef __USE_POSIX199309
/* Pause execution for a number of nanoseconds. */
extern int nanosleep __P ((__const struct timespec *__requested_time,
struct timespec *__remaining));
# endif

# ifdef __USE_XOPEN_EXTENDED
/* Set to one of the following values to indicate an error.
1 the DATEMSK environment variable is null or undefined,
2 the template file cannot be opened for reading,
3 failed to get file status information,
4 the template file is not a regular file,
5 an error is encountered while reading the template file,
6 memory allication failed (not enough memory available),
7 there is no line in the template that matches the input,
8 invalid input specification Example: February 31 or a time is
specified that can not be represented in a time_t (representing
the time in seconds since 00:00:00 UTC, January 1, 1970) */
extern int getdate_err;

/* Parse the given string as a date specification and return a value
representing the value. The templates from the file identified by
the environment variable DATEMSK are used. In case of an error
`getdate_err' is set. */
extern struct tm *getdate __P ((__const char *__string));
# endif

# ifdef __USE_GNU
/* Since `getdate' is not reentrant because of the use of `getdate_err'
and the static buffer to return the result in, we provide a thread-safe
variant. The functionality is the same. The result is returned in
the buffer pointed to by RESBUFP and in case of an error the return
value is != 0 with the same values as given above for `getdate_err'. */
extern int getdate_r __P ((__const char *__restrict __string,
struct tm *__restrict __resbufp));
# endif

__END_DECLS

#endif /* included. */

#endif /* not already included. */

你肯定有编译器吧？
直接去你的编译器的安装目录，找一下里面有个includes的文件夹，在里面你就能找到time.h的代码