R 在 1：36：14 而不是 2：00：00 从 PDT 切换到 PST - Lubridate 在切换前分配时区

这不是一个完整的答案，但我希望有更多专业知识的人可以在此基础上再接再厉。

as.POSIXct

在进入代码之前，我首先想提供一些上下文。我们从定义了多个方法的泛型函数开始。as.POSIXctS3

as.POSIXct
#> function (x, tz = "", ...)
#> UseMethod("as.POSIXct")

methods(as.POSIXct)
#> [1] as.POSIXct.Date    as.POSIXct.default as.POSIXct.numeric as.POSIXct.POSIXlt
#> see '?methods' for accessing help and source code

对于 OP 给出的示例，由于我们正在处理字符数据类型，因此我们将使用以下方法：default

as.POSIXct.default
#> function (x, tz = "", ...)
#> {
#>     if (inherits(x, "POSIXct"))
#>         return(if (missing(tz)) x else .POSIXct(x, tz))
#>     if (is.null(x))
#>         return(.POSIXct(numeric(), tz))
#>     if (is.character(x) || is.factor(x))
#>         return(as.POSIXct(as.POSIXlt(x, tz, ...), tz, ...))
#>     if (is.logical(x) && all(is.na(x)))
#>         return(.POSIXct(as.numeric(x), tz))
#>     stop(gettextf("do not know how to convert '%s' to class %s",
#>         deparse1(substitute(x)), dQuote("POSIXct")), domain = NA)
#> }

这使我们调用（上面的第三个条件）一个泛型函数，它恰好有一个字符方法：.我不会粘贴源代码，但该函数的核心是 .as.POSIXltS3as.POSIXlt.characterstrptime

strptime
#> function (x, format, tz = "")
#> .Internal(strptime(if (is.character(x)) x else if (is.object(x)) `names<-`(as.character(x),
#>     names(x)) else `storage.mode<-`(x, "character"), format, tz))

您可以在此处查看代码。我最初尝试从逻辑上遵循代码，但事实证明这非常困难。C

RApiDatetime

幸运的是，有一个包 RApiDatetime（感谢 Dirk！），它的功能是： .根据 OP 提供的值调用它，我们有：RApiDatetime::rapistrptime

RApiDatetime::rapistrptime(x, fmt = "%Y-%m-%d %H:%M:%OS", "PST8PDT")
#> $sec
#>  [1]  0  1  0  0 10 14 15 30 59  0 59  0  0
#>
#> $min
#>  [1]  0  0 35 36 36 36 36 36 36 45 59  0 30
#>
#> $hour
#>  [1] 1 1 1 1 1 1 1 1 1 1 1 2 2
#>
#> $mday
#>  [1] 7 7 7 7 7 7 7 7 7 7 7 7 7
#>
#> $mon
#>  [1] 10 10 10 10 10 10 10 10 10 10 10 10 10
#>
#> $year
#>  [1] 121 121 121 121 121 121 121 121 121 121 121 121 121
#>
#> $wday
#>  [1] 0 0 0 0 0 0 0 0 0 0 0 0 0
#>
#> $yday
#>  [1] 310 310 310 310 310 310 310 310 310 310 310 310 310
#>
#> $isdst
#>  [1] 1 1 1 1 1 1 0 0 0 0 0 0 0
#>
#> $zone
#>  [1] "PDT" "PDT" "PDT" "PDT" "PDT" "PDT" "PST" "PST" "PST" "PST" "PST" "PST" "PST"
#>
#> $gmtoff
#>  [1] NA NA NA NA NA NA NA NA NA NA NA NA NA
#>
#> attr(,"class")
#> [1] "POSIXlt" "POSIXt"
#> attr(,"tzone")
#> [1] "PST8PDT" "PST"     "PDT"

我们看到这个领域看起来值得研究。在克隆了 repo 并粗略地使用了 之后，我更容易遵循路径。我们发现背后的真正行动就发生在这里。isdstprintfisdist

.
.
    OK = tm->tm_year < 138 && tm->tm_year >= (have_broken_mktime() ? 70 : 02);
    if(OK) {
    res = (double) mktime(tm);
    if (res == -1.) return res;
.
.

mktime

最后，我们在评论中谈到了我的主张。mktime

我写了这个非常简单的函数来查看调用后我们的结构会发生什么：C++mktime

#include <Rcpp.h>
using namespace Rcpp;

#include <time.h>
#include <stdio.h>

// [[Rcpp::export]]
void CheckMkTime(int tm_sec) {
    struct tm info;

    info.tm_sec = tm_sec;
    info.tm_min = 36;
    info.tm_hour = 1;
    info.tm_mday = 7;
    info.tm_mon = 10;
    info.tm_year = 121;
    info.tm_wday = 0;
    info.tm_yday = 310;
    info.tm_isdst = -1;

    time_t val = mktime(&info);
    printf("mktime_res: %jd,\n tm_zone: %s,\n tm_gmtoff: %ld,\n tm_sec: %d,\n "
           "tm_min: %d,\n tm_hour: %d,\n tm_mday: %d,\n tm_mon: %d,\n "
           "tm_year: %d,\n tm_wday: %d,\n tm_yday: %d,\n tm_isdst: %d,\n",
           val,
           info.tm_zone,
           info.tm_gmtoff,
           info.tm_sec,
           info.tm_min,
           info.tm_hour,
           info.tm_mday,
           info.tm_mon,
           info.tm_year,
           info.tm_wday,
           info.tm_yday,
           info.tm_isdst);
}

并调用它，我们有：tm_sec = 14

CheckMkTime(14)
#> mktime_res: 1636274174,
#>  tm_zone: PDT,
#>  tm_gmtoff: -25200,
#>  tm_sec: 14,
#>  tm_min: 36,
#>  tm_hour: 1,
#>  tm_mday: 7,
#>  tm_mon: 10,
#>  tm_year: 121,
#>  tm_wday: 0,
#>  tm_yday: 310,
#>  tm_isdst: 1,

我们看到：tm_sec = 15

CheckMkTime(15)
#> mktime_res: 1636277775,
#>  tm_zone: PST,
#>  tm_gmtoff: -28800,
#>  tm_sec: 15,
#>  tm_min: 36,
#>  tm_hour: 1,
#>  tm_mday: 7,
#>  tm_mon: 10,
#>  tm_year: 121,
#>  tm_wday: 0,
#>  tm_yday: 310,
#>  tm_isdst: 0,

所以问题对吗？mktime

我不太确定...

我写了纯代码：C

#include <time.h>
#include <stdio.h>

int main(void) {
    struct tm info;

    info.tm_sec = 14;
    info.tm_min = 36;
    info.tm_hour = 1;
    info.tm_mday = 7;
    info.tm_mon = 10;
    info.tm_year = 121;
    info.tm_wday = 0;
    info.tm_yday = 310;
    info.tm_isdst = -1;

    time_t val = mktime(&info);
    printf("mktime_res: %jd,\n tm_zone: %s,\n tm_gmtoff: %ld,\n tm_sec: %d,\n "
               "tm_min: %d,\n tm_hour: %d,\n tm_mday: %d,\n tm_mon: %d,\n "
               "tm_year: %d,\n tm_wday: %d,\n tm_yday: %d,\n tm_isdst: %d\n",
               val,
               info.tm_zone,
               info.tm_gmtoff,
               info.tm_sec,
               info.tm_min,
               info.tm_hour,
               info.tm_mday,
               info.tm_mon,
               info.tm_year,
               info.tm_wday,
               info.tm_yday,
               info.tm_isdst);


    struct tm info2;
    info2.tm_sec = 15;
    info2.tm_min = 36;
    info2.tm_hour = 1;
    info2.tm_mday = 7;
    info2.tm_mon = 10;
    info2.tm_year = 121;
    info2.tm_wday = 0;
    info2.tm_yday = 310;
    info2.tm_isdst = -1;

    val = mktime(&info2);
    printf("\n\nmktime_res: %jd,\n tm_zone: %s,\n tm_gmtoff: %ld,\n tm_sec: %d,\n "
               "tm_min: %d,\n tm_hour: %d,\n tm_mday: %d,\n tm_mon: %d,\n "
               "tm_year: %d,\n tm_wday: %d,\n tm_yday: %d,\n tm_isdst: %d\n",
               val,
               info2.tm_zone,
               info2.tm_gmtoff,
               info2.tm_sec,
               info2.tm_min,
               info2.tm_hour,
               info2.tm_mday,
               info2.tm_mon,
               info2.tm_year,
               info2.tm_wday,
               info2.tm_yday,
               info2.tm_isdst);

    return 0;
}

编译了它，并在终端中运行了它：

% clang time_shift.c -o time_shift
% ./time_shift
#> mktime_res: 1636266974,
#>  tm_zone: EST,
#>  tm_gmtoff: -18000,
#>  tm_sec: 14,
#>  tm_min: 36,
#>  tm_hour: 1,
#>  tm_mday: 7,
#>  tm_mon: 10,
#>  tm_year: 121,
#>  tm_wday: 0,
#>  tm_yday: 310,
#>  tm_isdst: 0
#>
#>
#> mktime_res: 1636266975,
#>  tm_zone: EST,
#>  tm_gmtoff: -18000,
#>  tm_sec: 15,
#>  tm_min: 36,
#>  tm_hour: 1,
#>  tm_mday: 7,
#>  tm_mon: 10,
#>  tm_year: 121,
#>  tm_wday: 0,
#>  tm_yday: 310,
#>  tm_isdst: 0

我们在这里没有看到问题。但是，我们确实注意到在这两种情况下都是 is，而当我们在运行后运行它时，我们获得了 14 和 15。tm_zoneESTRRApiDatetime::rapistrptime(x, fmt = "%Y-%m-%d %H:%M:%OS", "PST8PDT")PSTPDT

有了这个，我在一个新的会话中重新运行了这些示例，并获得了与我们在纯实现中相同的结果。RC

在调用 base 后，我们在新会话中没有看到此行为。RstrptimeR

我试着查看 mktime 源代码，但它远远超出了我的范围。

会议信息

sessionInfo()
#> R version 4.3.1 (2023-06-16)
#> Platform: aarch64-apple-darwin20 (64-bit)
#> Running under: macOS Ventura 13.4.1
#>
#> Matrix products: default
#> BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
#> LAPACK: /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.11.0
#>
#> locale:
#> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
#>
#> time zone: PST8PDT
#> tzcode source: internal
#>
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base
#>
#> other attached packages:
#> [1] RApiDatetime_0.0.8
#>
#> loaded via a namespace (and not attached):
#> [1] compiler_4.3.1 tools_4.3.1    Rcpp_1.0.11