哦，clock_gettime( ) 提供了纳秒的精确度，给程序计时可是不错哦；
函数的原型如下：
int clock_gettime(clockid_t clk_id, struct timespect * tp);
clockid_t clk_id用于指定计时时钟的类型，对于我们Programmr以下三种比较常用：
CLOCK_REALTIME, a system-wide realtime clock.
CLOCK_PROCESS_CPUTIME_ID, high-resolution timer provided by the CPU for each process.
CLOCK_THREAD_CPUTIME_ID, high-resolution timer provided by the CPU for each of the threads.
CLOCK_REALTIME, a system-wide realtime clock.
CLOCK_PROCESS_CPUTIME_ID, high-resolution timer provided by the CPU for each process.
CLOCK_THREAD_CPUTIME_ID, high-resolution timer provided by the CPU for each of the threads.
struct timespect *tp用来存储当前的时间，其结构如下：
1
struct
timespec {
2
time_t tv_sec;
/*
seconds
*/
3
long
tv_nsec;
/*
nanoseconds
*/
4
};
呵呵，好啦！该讲的都刚清楚了，下面我们就上代码把；
代码
1
#include
<
iostream
>
2
#include
<
time.h
>
3
using
namespace
std;
4
5
timespec diff(timespec start, timespec end);
6
7
int
main()
8
{
9
timespec time1, time2;
10
int
temp;
11
clock_gettime(CLOCK_PROCESS_CPUTIME_ID,
&
time1);
12
for
(
int
i
=
0
; i
<
242000000
; i
++
)
13
temp
+=
temp;
14
clock_gettime(CLOCK_PROCESS_CPUTIME_ID,
&
time2);
15
cout
<<
diff(time1,time2).tv_sec
<<
"
:
"
<<
diff(time1,time2).tv_nsec
<<
endl;
16
return
0
;
17
}
18
19
timespec diff(timespec start, timespec end)
20
{
21
timespec temp;
22
if
((end.tv_nsec
-
start.tv_nsec)
<
0
) {
23
temp.tv_sec
=
end.tv_sec
-
start.tv_sec
-
1
;
24
temp.tv_nsec
=
1000000000
+
end.tv_nsec
-
start.tv_nsec;
25
}
else
{
26
temp.tv_sec
=
end.tv_sec
-
start.tv_sec;
27
temp.tv_nsec
=
end.tv_nsec
-
start.tv_nsec;
28
}
29
return
temp;
30
}