今天把在日照写的代码拿出来看了看，编译运行了一下，发生了一个意想不到的事：用来测时间的 clock() 函数返回了一个非常大的数……正常应该返回毫秒数啊。无奈，上网看了一下。看了一下 clock() 函数的介绍。
Returns the number of clock ticks elapsed since the program was launched.
The macro constant expression CLOCKS_PER_SEC specifies the relation between a clock tick and a second (clock ticks per second).
The initial moment of reference used by clock as the beginning of the program execution may vary between platforms. To calculate the actual processing times of a program, the value returned by clock should be compared to a value returned by an initial call to clock.
原来返回的并不是毫秒数，而是一个number of clock，常量 CLOCKS_PER_SEC 定义了 clock 和秒数之间的关系，返回毫秒数应该用clock()*1000/CLOCKS_PER_SEC，而不是仅仅用 clock() 。Dev-C++自带的gcc3.4.2中CLOCKS_PER_SEC=1000，所以 clock() 正好返回毫秒数，我用的gcc4.1.2里CLOCKS_PER_SEC=1000000，返回的数当然大了。
今天又纠正了一个错误，不错。
PS：本来不想在这个 blog 里说关于 Programming 的东西的，想再开一个 blog ，现在懒得干了 ，不学 Programming 的同学们就不要看这些 post 了。
Tags:C++,OI,programmingRelated Posts
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