clock()与time()区别

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最新推荐文章于 2025-06-11 17:52:02 发布

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分类专栏： C-C++ Linux

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本文详细介绍了C语言中的两个常用时间函数：clock() 和 time()。clock() 函数用于获取程序运行过程中消耗的CPU时间，以系统特定的时钟刻度为单位；time() 函数则用于获取自1970年1月1日以来的秒数，常用于记录实际的时间流逝。文章对比了这两个函数的不同应用场景，并给出了使用建议。

1. clock

clock_t clock (void);

Clock program
Returns the processor time consumed by the program.

The value returned is expressed in clock ticks,
which are units of time of a constant but system-specific length 
(with a relation of CLOCKS_PER_SEC clock ticks per second).

The epoch used as reference by clock varies between systems,
but it is related to the program execution (generally its launch). 
To calculate the actual processing time of a program, 
the value returned by clock shall be compared to a value 
returned by a previous call to the same function.

2. time

time_t time (time_t* timer);
Get current time
Get the current calendar time as a value of type time_t.

The function returns this value, 
and if the argument is not a null pointer, 
it also sets this value to the object pointed by timer.

The value returned generally represents the number of seconds 
since 00:00 hours, Jan 1, 1970 UTC (i.e., the current unix timestamp). 
Although libraries may use a different representation of time: 
Portable programs should not use the value returned by this function directly, 
but always rely on calls to other elements of the standard library 
to translate them to portable types (such as localtime, gmtime or difftime).

3. 区别

clock()返回从“开启这个程序进程”到“程序中调用clock()函数”时之间的CPU时钟计时单元（clock tick）数，sleep(5)并不占用cpu资源，
导致start1和end1返回的值一样。
time(&temp)返回从CUT（Coordinated Universal Time）时间1970年1月1日00:00:00（称为UNIX系统的Epoch时间）到当前时刻的秒数。
总之，用time_t计时才是人们正常意识上的秒数，而clock_t计时所表示的是占用CPU的时钟单元。