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LINUX C系统编程与PYTHON中的时间模块对比

今天看python时间模块time的时候发现和LINUX系统编程中的时间调用函数基本一样,以前刚好没有好好学习LINUX C编程的时间模块就对比进行了学习。

  • 本文只是给出函数接口和使用方式,详细了解请参考LINUX main page和PYTHON help
  • 本文不涉及asctime和ctime,并且C中涉及多线程编程注意选择可重入性函数

一、时间存在方式

其实不管是C还是PYTHON这里都包含3种时间不同存在的方式

  • 日历时间:Epoch以来的秒及新纪元时间(1970年1月1日 00:00:00)以来的秒
  • 分解时间:实际上是时间在程序内部存在的结构,也是一个中间介质,C中使用结构体,PYTHON中使用元组
  1. LINUX C为tm结构体:
struct tm {                int tm_sec;         /* seconds */                int tm_min;         /* minutes */                int tm_hour;        /* hours */                int tm_mday;        /* day of the month */                int tm_mon;         /* month */                int tm_year;        /* year */                int tm_wday;        /* day of the week */                int tm_yday;        /* day in the year */                int tm_isdst;       /* daylight saving time */                                    /* >0 DST is in effect                                       =0 DST is not effect;                                       <0 DST information not available                                     */                     }; 
  1. PYTHON struct_time元组:
索引(Index)   属性(Attribute)     0               tm_year(年)       1               tm_mon(月)      2               tm_mday(日)    3               tm_hour(时)    4               tm_min(分)      5               tm_sec(秒)     6               tm_wday(weekday)       7               tm_yday(一年中的第几天)      8               tm_isdst(是否是夏令时) 

可以看到他们基本是一致的

  • 可读时间:这种一般就是我们平时看到的一些方便读取的的时间,比如
2017-10-12 06:52:03(AM) +0800 

就是方便人类读取的可读取时间

LINUX C可读时间格式:

%a     The abbreviated weekday name according to the current locale.  %A     The full weekday name according to the current locale.  %b     The abbreviated month name according to the current locale.  %B     The full month name according to the current locale.  %c     The preferred date and time representation for the current locale.  %C     The century number (year/100) as a 2-digit integer. (SU)  %d     The day of the month as a decimal number (range 01 to 31).  %D     Equivalent  to  %m/%d/%y.   (Yecch—for  Americans only.  Americans should note that in other countries %d/%m/%y is rather common.  This means that in        international context this format is ambiguous and should not be used.) (SU)  %e     Like %d, the day of the month as a decimal number, but a leading zero is replaced by a space. (SU)  %E     Modifier: use alternative format, see below. (SU)  %F     Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)  %G     The ISO 8601 week-based year (see NOTES) with century as a decimal number.  The 4-digit year corresponding to the ISO week number (see %V).  This has        the same format and value as %Y, except that if the ISO week number belongs to the previous or next year, that year is used instead. (TZ)  %g     Like %G, but without century, that is, with a 2-digit year (00-99). (TZ)  %h     Equivalent to %b.  (SU)  %H     The hour as a decimal number using a 24-hour clock (range 00 to 23).  %I     The hour as a decimal number using a 12-hour clock (range 01 to 12).  %j     The day of the year as a decimal number (range 001 to 366).  %k     The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank.  (See also %H.)  (TZ)  %l     The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank.  (See also %I.)  (TZ)  %m     The month as a decimal number (range 01 to 12).  %M     The minute as a decimal number (range 00 to 59).  %n     A newline character. (SU)  %O     Modifier: use alternative format, see below. (SU)  %p     Either  "AM" or "PM" according to the given time value, or the corresponding strings for the current locale.  Noon is treated as "PM" and midnight as        "AM".  %P     Like %p but in lowercase: "am" or "pm" or a corresponding string for the current locale. (GNU)  %r     The time in a.m. or p.m. notation.  In the POSIX locale this is equivalent to %I:%M:%S %p.  (SU)  %R     The time in 24-hour notation (%H:%M).  (SU) For a version including the seconds, see %T below.  %s     The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). (TZ)  %S     The second as a decimal number (range 00 to 60).  (The range is up to 60 to allow for occasional leap seconds.)  %t     A tab character. (SU)  %T     The time in 24-hour notation (%H:%M:%S).  (SU)  %u     The day of the week as a decimal, range 1 to 7, Monday being 1.  See also %w.  (SU)  %U     The week number of the current year as a decimal number, range 00 to 53, starting with the first Sunday as the first day of week 01.  See also %V and        %W.  %V     The ISO 8601 week number (see NOTES) of the current year as a decimal number, range 01 to 53, where week 1 is the first week that has at least 4 days        in the new year.  See also %U and %W.  (SU)  %w     The day of the week as a decimal, range 0 to 6, Sunday being 0.  See also %u.  %W     The week number of the current year as a decimal number, range 00 to 53, starting with the first Monday as the first day of week 01.  %x     The preferred date representation for the current locale without the time.  %X     The preferred time representation for the current locale without the date.  %y     The year as a decimal number without a century (range 00 to 99).  %Y     The year as a decimal number including the century.  %z     The +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC). (SU)  %Z     The timezone name or abbreviation.  %+     The date and time in date(1) format. (TZ) (Not supported in glibc2.)  %%     A literal '%' character. 

python 可读时间格式:

%Y  Year with century as a decimal number.  %m  Month as a decimal number [01,12].  %d  Day of the month as a decimal number [01,31].  %H  Hour (24-hour clock) as a decimal number [00,23].  %M  Minute as a decimal number [00,59].  %S  Second as a decimal number [00,61].  %z  Time zone offset from UTC.  %a  Locale's abbreviated weekday name.  %A  Locale's full weekday name.  %b  Locale's abbreviated month name.  %B  Locale's full month name.  %c  Locale's appropriate date and time representation.  %I  Hour (12-hour clock) as a decimal number [01,12].  %p  Locale's equivalent of either AM or PM.    Other codes may be available on your platform.  See documentation for  the C library strftime function. 

本文使用这三个术语

二、日历时间

下面方法获取当前系统时间的当前时间

  • LINUX C:
    int gettimeofday(struct timeval *tv,struct timezone *tz);
    time_t time(time_t *timep)
  • PYTHON:
    time.time()
    上面的方式都是获取当前时间的日历时间的方式为了方便我们使用time方法

三、日历时间转换为分解时间

  • LINUX C:
    strcut tm* gmtime(const time_t* timep);
    strcut tm* localtime(const time_t* timep);
Each of these functions returns the value described, or NULL  in case an error was detected. 
  • PYTHON:
    time.gmtime(seconds=None)
    time.localtime(seconds=None)

可以看到他们是一致的其中gmtime代表返回UTC时间,而localtime代表返回本地时区时间

四、将分解时间转换为日历时间

  • LINUX C:
    time_t mktime(struct tm* tmieptr)
RETURN VALUE        -1 in case of mktime() in case an error was detected. 
  • PYTHON:
    time.mktime(p_tuple)

五、将分解时间转换为可读时间

  • LINUX C:
    size_t strftime(char *s, size_t max, const char *format,const struct tm *tm);
RETURN VALUE        Provided that the result string, including the terminating null byte, does not exceed max bytes, strftime() returns the number of bytes (excluding the ter‐        minating  null  byte)  placed  in the array s.  If the length of the result string (including the terminating null byte) would exceed max bytes, then strf‐        time() returns 0, and the contents of the array are undefined.  (This behavior applies since at least libc 4.4.4; very old versions of libc, such  as  libc        4.4.1, would return max if the array was too small.)          Note  that the return value 0 does not necessarily indicate an error.  For example, in many locales %p yields an empty string.  An empty format string will        likewise yield an empty string. 
  • PYTHON:
    strftime(format, p_tuple=None)

这里需要注意format,format在文章开头已经给出

六、将可读时间转换为分解时间

  • LINUX C:
    char *strptime(const char *s, const char *format, struct tm *tm);
RETURN VALUE        The return value of the function is a pointer to the first character not processed in this function call.  In case the input string contains  more  charac‐        ters  than required by the format string the return value points right after the last consumed input character.  In case the whole input string is consumed        the return value points to the null byte at the end of the string.  If strptime() fails to match all of the format string and therefore an  error  occurred        the function returns NULL. 
  • PYTHON:
    strptime(string, format)
    这里需要注意format,format在文章开头已经给出

七、转换图

这里给出一张LINUX系统编程手册里面的一张图,其实python是一样的,红色箭头是本文涉及的函数

Paste_Image.png

Paste_Image.png

八、方法使用举例

下面使用C和PYTHON分别实现将日期

2017-10-12 08:52:03(AM) CST 

转换分解时间,日历时间然后再减去3600秒转换回分解时间和可读时间的小程序,以熟悉使用方式

  • C程序:
/*************************************************************************   > File Name: testtime.c   > Author: gaopeng QQ:22389860 all right reserved   > Mail: gaopp_200217@163.com   > Created Time: Wed 01 Nov 2017 02:28:25 AM CST  ************************************************************************/    #include<stdio.h>  #include<time.h>  #include<stdlib.h>  #define MAXSIZE 99      int  rtime2ctime(/*in*/const char* r_time,/*out*/time_t* ctime)  {         time_t i_ctime;         struct tm tm_st;         //此处根据固定测试转换为分解时间tm_st         if ( !strptime(r_time,"%Y-%m-%d %X(%p) %z",&tm_st))         {                 return -1;         }           //此处将分解时间tm_st转换为日历时间ctime         if( (*ctime = mktime(&tm_st)) == -1)         {                 return -1;         }           return 0;  }      int ctime2rtime(/*in*/time_t c_time)  {           struct tm* tm_st = NULL;         char time[MAXSIZE] ;         //此处将日历时间转换为分解时间         if((tm_st = localtime(&c_time)) == NULL)         {                 return -1;         }             //此处将分解时间转换为可读时间         if(strftime(time,MAXSIZE-1,"%Y-%m-%d %X(%p) %z",tm_st) == 0)         {                 return -1;         }           printf("%sn",time);         return 0;  }        int main(void)  {         char r_time[100] = "2017-10-12 07:52:03(AM) +0800";         time_t ctime;           if( rtime2ctime(r_time,&ctime) == -1 )         {                 printf("rtime2ctime errorn");                 return -1;         }           printf("2017-10-12 07:52:03(AM) +0800 to calenlar time is:%ldn",ctime);           ctime = ctime - (time_t)3600;             printf("after sub 1 hours time is:");           if(ctime2rtime(ctime) == -1)         {                 printf("ctime2rtime errorn");         }    } 
  • python程序:
import time    def rtime2ctime(r_time):      #此处根据固定测试可读时间转换为分解时间      p_time = time.strptime(r_time,"%Y-%m-%d %X(%p) %z")      #此处将分解时间tm_st转换为日历时间      return time.mktime(p_time)    def ctime2rtime(ctime):      #此处将日历时间转换为分解时间      p_time = time.localtime(ctime)      #此处将分解时间转换为可读时间      r_time = time.strftime("%Y-%m-%d %X(%p) %z",p_time)      return r_time    r_time="2017-10-12 06:52:03(AM) +0800"  ctime = rtime2ctime(r_time)  print("2017-10-12 06:52:03(AM) +0800 to calenlar time is:%d" %(ctime))  ctime = ctime - 3600  print("after sub 1 hours time is:%s" %(ctime2rtime(ctime))) 

他们的运行结果均是:

2017-10-12 06:52:03(AM) +0800 to calenlar time is:1507762323  after sub 1 hours time is:2017-10-12 05:52:03(AM) +0800 

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来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/7728585/viewspace-2145919/,如需转载,请注明出处,否则将追究法律责任。

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