CPU Time - CLOCKS_PER_SEC

Dear 丶 2023-03-13 13:11 9阅读 0赞

#  CPU Time - CLOCKS\_PER\_SEC #

## 1. CPU Time Inquiry ##

To get a process’ CPU time, you can use the `clock` function. This facility is declared in the header file `time.h`.  
要获取进程的 CPU 时间，您可以使用 `clock` 函数。此功能在头文件 `time.h` 中声明。

In typical usage, you call the `clock` function at the beginning and end of the interval you want to time, subtract the values, and then divide by `CLOCKS_PER_SEC` (the number of clock ticks per second) to get processor time, like this:  
在典型用法中，您在要计时的时间间隔的开始和结束时调用 `clock` 函数，相减然后除以 `CLOCKS_PER_SEC`(每秒的时钟滴答数) 即可获得处理器时间，如下所示：

/*
    ============================================================================
    Name        : foreverstrong.c
    Author      : Yongqiang Cheng
    Version     : Version 1.0.0
    Copyright   : Copyright (c) 2020 Yongqiang Cheng
    Description : Hello World in C, Ansi-style
    ============================================================================
    */
    
    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
    
    int main(void)
    {
    	clock_t start = 0, end = 0;
    	double cpu_time_used = 0;
    
    	start = clock();
    	printf("Start of the program, start = %ld\n", start);
    
    	printf("Start of the program, start = %ld\n", start);
    
    	puts("!!!Hello World!!!"); /* prints !!!Hello World!!! */
    
    	end = clock();
    	printf("End of the program, end_t = %ld\n", end);
    
    	printf("End of the program, end_t = %ld\n", end);
    
    	cpu_time_used = ((double)(end - start)) / CLOCKS_PER_SEC;
    	printf("Total time taken by CPU: %f\n", cpu_time_used);
    
    	printf("Exiting of the program...\n");
    
    	return EXIT_SUCCESS;
    }

Start of the program, start = 0
    Start of the program, start = 0
    !!!Hello World!!!
    End of the program, end_t = 0
    End of the program, end_t = 0
    Total time taken by CPU: 0.000000
    Exiting of the program...
    请按任意键继续. . .

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXExMTY_size_16_color_FFFFFF_t_70_pic_center]

Do not use a single CPU time as an amount of time; it doesn’t work that way. Either do a subtraction as shown above or query processor time directly.  
不要将单个 CPU 时间用作时间量。这样是行不通的。如上所示进行减法或直接查询处理器时间。

Different computers and operating systems vary wildly in how they keep track of CPU time. It’s common for the internal processor clock to have a resolution somewhere between a hundredth and millionth of a second.  
不同的计算机和操作系统在跟踪 CPU 时间方面有很大的不同。内部处理器时钟的分辨率通常在百分之一秒和百万分之一秒之间。

**Macro**: `int CLOCKS_PER_SEC`  
The value of this macro is the number of clock ticks per second measured by the `clock` function. POSIX requires that this value be one million independent of the actual resolution.  
这个宏的值是由 `clock` 函数测量的每秒时钟滴答数。POSIX 要求该值应为一百万，与实际分辨率无关。

**Function**: `clock_t clock (void)`

This function returns the calling process’ current CPU time. If the CPU time is not available or cannot be represented, `clock` returns the value `(clock_t)(-1)`.  
此函数返回调用进程的当前 CPU 时间。如果 CPU 时间不可用或无法表示，则 `clock` 返回值 `(clock_t)(-1)`。

## 2. Processor Time Inquiry ##

The `times` function returns information about a process’ consumption of processor time in a `struct tms` object, in addition to the process’ CPU time. You should include the header file `sys/times.h` to use this facility.  
`times` 函数除了返回进程的 CPU 时间之外，在 `struct tms` 对象中返回有关进程消耗的处理器时间信息。您应该包括头文件 `sys/times.h` 以使用此功能。

## 3. Date and Time ##

[http://kirste.userpage.fu-berlin.de/chemnet/use/info/libc/libc\_17.html][http_kirste.userpage.fu-berlin.de_chemnet_use_info_libc_libc_17.html]

Functions for measuring elapsed CPU time are discussed in section Processor Time. (测量经过的 CPU 时间的功能)  
Functions for measuring absolute clock or calendar time are discussed in section Calendar Time. (测量绝对时钟或日历时间)  
Functions for setting alarms and timers are discussed in section Setting an Alarm. (设置警报和计时器)

## References ##

[https://www.gnu.org/software/libc/manual/html\_node/CPU-Time.html][https_www.gnu.org_software_libc_manual_html_node_CPU-Time.html]  
[https://www.gnu.org/software/libc/manual/html\_node/Processor-Time.html][https_www.gnu.org_software_libc_manual_html_node_Processor-Time.html]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXExMTY_size_16_color_FFFFFF_t_70_pic_center]: /images/20230312/778ee4abcbff47d7b89239f455250daa.png
[http_kirste.userpage.fu-berlin.de_chemnet_use_info_libc_libc_17.html]: http://kirste.userpage.fu-berlin.de/chemnet/use/info/libc/libc_17.html
[https_www.gnu.org_software_libc_manual_html_node_CPU-Time.html]: https://www.gnu.org/software/libc/manual/html_node/CPU-Time.html
[https_www.gnu.org_software_libc_manual_html_node_Processor-Time.html]: https://www.gnu.org/software/libc/manual/html_node/Processor-Time.html