c++ - C/C++ : how to get integer unix timestamp of build time (not string)

Question

我正在尝试实现非常微不足道的事情:我需要存储构建时间的整数 32 位 unix 时间戳，但是我找到的所有宏 (__DATE__, __TIME__ , __TIMESTAMP__) 扩展为字符串，而不是整数。

看来，我们只是没有它(这对我来说很奇怪)。我真的想要整数，而不是字符串。

获得它的最佳做法是什么？

更新:

附带说明:我做嵌入式的东西，所以我没有足够的资源(比如 128 KB 的闪存)，因此解析字符串真的是个坏主意。

我为什么需要它:我只需要每个 Beta 版本都有唯一的版本号。首先，hex 文件将被命名为 my-firmware-v2-33-BETA-1397315745.hex，其次，当我需要在设备屏幕上显示当前版本时，我可能想要回显它各种格式。

Answer 1

所以，今晚我玩得很开心，创建了一个带有宏的头文件来生成 UNIX 时间戳，没有任何外部程序或特殊的编译器功能! 只需包含 header 并使用 __TIME_UNIX__ 宏。

其实代码很简单:

1. 按照 loreb 的建议，使用 str[i]-'0' 将字符串中的数字字符转换为数字，并根据它们的位置进行权衡。
2. 月份字符串的处理方式与chux 答案类似；字符被单独检查并作为一个组与 ? : 运算符。
3. 计算上个月的天数是用可交换的 完成的？ : 表达式。
4. 闰年的计算很简单，因为在 UNIX 时间框架内每 4 年插入一个闰日
5. 最后，所有单独的值都与相应的秒数进行权衡以获得 UNIX 时间。请注意，SEC_PER_DAY 必须减去一次，因为 JAN 01 1970, 00:00:00 必须是 0。

代码已在 ATMEL Studio 7 (Visual Studio 2015) 中使用默认编译器和设置(avr-gcc、-O1 优化)进行测试，结果已通过检查生成的 .lss 文件得到确认。

将下面的代码复制并粘贴到一个头文件中，并将其包含在您需要的任何位置。享受吧!

/*
 * compile_time.h
 *
 * Created: 30.05.2017 20:57:58
 *  Author: Dennis (instructable.com/member/nqtronix)
 *
 * This code provides the macro __TIME_UNIX__ which returns the current time in UNIX format. It can
 * be used to identify a version of code on an embedded device, to initialize its RTC and much more.
 * Along that several more constants for seconds, minutes, etc. are provided
 *
 * The macro is based on __TIME__ and __DATE__, which are assumed to be formatted "HH:MM:SS" and
 * "MMM DD YYYY", respectively. The actual value can be calculated by the C compiler at compile time
 * as all inputs are literals. MAKE SURE TO ENABLE OPTIMISATION!
 */ 


#ifndef COMPILE_TIME_H_
#define COMPILE_TIME_H_

// extracts 1..4 characters from a string and interprets it as a decimal value
#define CONV_STR2DEC_1(str, i)  (str[i]>'0'?str[i]-'0':0)
#define CONV_STR2DEC_2(str, i)  (CONV_STR2DEC_1(str, i)*10 + str[i+1]-'0')
#define CONV_STR2DEC_3(str, i)  (CONV_STR2DEC_2(str, i)*10 + str[i+2]-'0')
#define CONV_STR2DEC_4(str, i)  (CONV_STR2DEC_3(str, i)*10 + str[i+3]-'0')

// Some definitions for calculation
#define SEC_PER_MIN             60UL
#define SEC_PER_HOUR            3600UL
#define SEC_PER_DAY             86400UL
#define SEC_PER_YEAR            (SEC_PER_DAY*365)
#define UNIX_START_YEAR         1970UL

// Custom "glue logic" to convert the month name to a usable number
#define GET_MONTH(str, i)      (str[i]=='J' && str[i+1]=='a' && str[i+2]=='n' ? 1 :     \
                                str[i]=='F' && str[i+1]=='e' && str[i+2]=='b' ? 2 :     \
                                str[i]=='M' && str[i+1]=='a' && str[i+2]=='r' ? 3 :     \
                                str[i]=='A' && str[i+1]=='p' && str[i+2]=='r' ? 4 :     \
                                str[i]=='M' && str[i+1]=='a' && str[i+2]=='y' ? 5 :     \
                                str[i]=='J' && str[i+1]=='u' && str[i+2]=='n' ? 6 :     \
                                str[i]=='J' && str[i+1]=='u' && str[i+2]=='l' ? 7 :     \
                                str[i]=='A' && str[i+1]=='u' && str[i+2]=='g' ? 8 :     \
                                str[i]=='S' && str[i+1]=='e' && str[i+2]=='p' ? 9 :     \
                                str[i]=='O' && str[i+1]=='c' && str[i+2]=='t' ? 10 :    \
                                str[i]=='N' && str[i+1]=='o' && str[i+2]=='v' ? 11 :    \
                                str[i]=='D' && str[i+1]=='e' && str[i+2]=='c' ? 12 : 0)

#define GET_MONTH2DAYS(month)  ((month == 1 ? 0 : 31 +                      \
                                (month == 2 ? 0 : 28 +                      \
                                (month == 3 ? 0 : 31 +                      \
                                (month == 4 ? 0 : 30 +                      \
                                (month == 5 ? 0 : 31 +                      \
                                (month == 6 ? 0 : 30 +                      \
                                (month == 7 ? 0 : 31 +                      \
                                (month == 8 ? 0 : 31 +                      \
                                (month == 9 ? 0 : 30 +                      \
                                (month == 10 ? 0 : 31 +                     \
                                (month == 11 ? 0 : 30))))))))))))           \


#define GET_LEAP_DAYS           ((__TIME_YEARS__-1968)/4 - (__TIME_MONTH__ <=2 ? 1 : 0))



#define __TIME_SECONDS__        CONV_STR2DEC_2(__TIME__, 6)
#define __TIME_MINUTES__        CONV_STR2DEC_2(__TIME__, 3)
#define __TIME_HOURS__          CONV_STR2DEC_2(__TIME__, 0)
#define __TIME_DAYS__           CONV_STR2DEC_2(__DATE__, 4)
#define __TIME_MONTH__          GET_MONTH(__DATE__, 0)
#define __TIME_YEARS__          CONV_STR2DEC_4(__DATE__, 7)

#define __TIME_UNIX__         ((__TIME_YEARS__-UNIX_START_YEAR)*SEC_PER_YEAR+       \
                                GET_LEAP_DAYS*SEC_PER_DAY+                          \
                                GET_MONTH2DAYS(__TIME_MONTH__)*SEC_PER_DAY+         \
                                __TIME_DAYS__*SEC_PER_DAY-SEC_PER_DAY+              \
                                __TIME_HOURS__*SEC_PER_HOUR+                        \
                                __TIME_MINUTES__*SEC_PER_MIN+                       \
                                __TIME_SECONDS__)

#endif /* COMPILE_TIME_H_ */

编辑:

初始版本不考虑 100 和 400 模年对 2 月天数的影响。这应该不是 2001 和 2101 之间的问题，但这里有一个更通用的宏:

/* 
 *
 * Created: 29.03.2018
 *
 * Authors:
 * 
 * Assembled from the code released on Stackoverflow by:
 *   Dennis (instructable.com/member/nqtronix)    |   https://stackoverflow.com/questions/23032002/c-c-how-to-get-integer-unix-timestamp-of-build-time-not-string
 * and
 *   Alexis Wilke                                 |   https://stackoverflow.com/questions/10538444/do-you-know-of-a-c-macro-to-compute-unix-time-and-date
 *
 * Assembled by Jean Rabault
 * 
 * UNIX_TIMESTAMP gives the UNIX timestamp (unsigned long integer of seconds since 1st Jan 1970) of compilation from macros using the compiler defined __TIME__ macro.
 * This should include Gregorian calendar leap days, in particular the 29ths of February, 100 and 400 years modulo leaps.
 * 
 * Careful: __TIME__ is the local time of the computer, NOT the UTC time in general!
 * 
 */

#ifndef COMPILE_TIME_H_
#define COMPILE_TIME_H_

// Some definitions for calculation
#define SEC_PER_MIN             60UL
#define SEC_PER_HOUR            3600UL
#define SEC_PER_DAY             86400UL
#define SEC_PER_YEAR            (SEC_PER_DAY*365)

// extracts 1..4 characters from a string and interprets it as a decimal value
#define CONV_STR2DEC_1(str, i)  (str[i]>'0'?str[i]-'0':0)
#define CONV_STR2DEC_2(str, i)  (CONV_STR2DEC_1(str, i)*10 + str[i+1]-'0')
#define CONV_STR2DEC_3(str, i)  (CONV_STR2DEC_2(str, i)*10 + str[i+2]-'0')
#define CONV_STR2DEC_4(str, i)  (CONV_STR2DEC_3(str, i)*10 + str[i+3]-'0')

// Custom "glue logic" to convert the month name to a usable number
#define GET_MONTH(str, i)      (str[i]=='J' && str[i+1]=='a' && str[i+2]=='n' ? 1 :     \
                                str[i]=='F' && str[i+1]=='e' && str[i+2]=='b' ? 2 :     \
                                str[i]=='M' && str[i+1]=='a' && str[i+2]=='r' ? 3 :     \
                                str[i]=='A' && str[i+1]=='p' && str[i+2]=='r' ? 4 :     \
                                str[i]=='M' && str[i+1]=='a' && str[i+2]=='y' ? 5 :     \
                                str[i]=='J' && str[i+1]=='u' && str[i+2]=='n' ? 6 :     \
                                str[i]=='J' && str[i+1]=='u' && str[i+2]=='l' ? 7 :     \
                                str[i]=='A' && str[i+1]=='u' && str[i+2]=='g' ? 8 :     \
                                str[i]=='S' && str[i+1]=='e' && str[i+2]=='p' ? 9 :     \
                                str[i]=='O' && str[i+1]=='c' && str[i+2]=='t' ? 10 :    \
                                str[i]=='N' && str[i+1]=='o' && str[i+2]=='v' ? 11 :    \
                                str[i]=='D' && str[i+1]=='e' && str[i+2]=='c' ? 12 : 0)

// extract the information from the time string given by __TIME__ and __DATE__
#define __TIME_SECONDS__        CONV_STR2DEC_2(__TIME__, 6)
#define __TIME_MINUTES__        CONV_STR2DEC_2(__TIME__, 3)
#define __TIME_HOURS__          CONV_STR2DEC_2(__TIME__, 0)
#define __TIME_DAYS__           CONV_STR2DEC_2(__DATE__, 4)
#define __TIME_MONTH__          GET_MONTH(__DATE__, 0)
#define __TIME_YEARS__          CONV_STR2DEC_4(__DATE__, 7)

// Days in February
#define _UNIX_TIMESTAMP_FDAY(year) \
    (((year) % 400) == 0UL ? 29UL : \
        (((year) % 100) == 0UL ? 28UL : \
            (((year) % 4) == 0UL ? 29UL : \
                28UL)))

// Days in the year
#define _UNIX_TIMESTAMP_YDAY(year, month, day) \
    ( \
        /* January */    day \
        /* February */ + (month >=  2 ? 31UL : 0UL) \
        /* March */    + (month >=  3 ? _UNIX_TIMESTAMP_FDAY(year) : 0UL) \
        /* April */    + (month >=  4 ? 31UL : 0UL) \
        /* May */      + (month >=  5 ? 30UL : 0UL) \
        /* June */     + (month >=  6 ? 31UL : 0UL) \
        /* July */     + (month >=  7 ? 30UL : 0UL) \
        /* August */   + (month >=  8 ? 31UL : 0UL) \
        /* September */+ (month >=  9 ? 31UL : 0UL) \
        /* October */  + (month >= 10 ? 30UL : 0UL) \
        /* November */ + (month >= 11 ? 31UL : 0UL) \
        /* December */ + (month >= 12 ? 30UL : 0UL) \
    )

// get the UNIX timestamp from a digits representation
#define _UNIX_TIMESTAMP(year, month, day, hour, minute, second) \
    ( /* time */ second \
                + minute * SEC_PER_MIN \
                + hour * SEC_PER_HOUR \
    + /* year day (month + day) */ (_UNIX_TIMESTAMP_YDAY(year, month, day) - 1) * SEC_PER_DAY \
    + /* year */ (year - 1970UL) * SEC_PER_YEAR \
                + ((year - 1969UL) / 4UL) * SEC_PER_DAY \
                - ((year - 1901UL) / 100UL) * SEC_PER_DAY \
                + ((year - 1601UL) / 400UL) * SEC_PER_DAY \
    )

// the UNIX timestamp
#define UNIX_TIMESTAMP (_UNIX_TIMESTAMP(__TIME_YEARS__, __TIME_MONTH__, __TIME_DAYS__, __TIME_HOURS__, __TIME_MINUTES__, __TIME_SECONDS__))

#endif