如何在linux下修改系统时间的函数？

Standard C Library Functions gettimeofday(3C)

NAME
gettimeofday, settimeofday - get or set the date and time

SYNOPSIS
#include <sys/time.h>

#include <unistd.h>

int gettimeofday(struct timeval *tp, void *);

int settimeofday(struct timeval *tp, void *);

DESCRIPTION
The gettimeofday() function gets and the settimeofday()
function sets the system's notion of the current time. The
current time is expressed in elapsed seconds and
microseconds since 00:00 Universal Coordinated Time, January
1, 1970. The resolution of the system clock is hardware
dependent; the time may be updated continuously or in clock
ticks.

The tp argument points to a timeval structure, which
includes the following members:

long tv_sec; /* seconds since Jan. 1, 1970 */
long tv_usec; /* and microseconds */

If tp is a null pointer, the current time information is not
returned or set.

The TZ environment variable holds time zone information. See
TIMEZONE(4).

The second argument to gettimeofday() and settimeofday()
should be a pointer to NULL.

Only the super-user may set the time of day.

RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is
returned and errno is set to indicate the error.

settimeofday(const struct timeval * t , const struct timezone *tzv )