perl - 为什么 POSIX 与 Win32 一起使用 floor() 抛出警告？

Question

我在下面写了以下比较简单的代码，抛出一个弹出框来提醒我日常任务。

#use Math::Round;
use POSIX;
use Win32;

use strict;
use warnings;

my $basetime = 1484784000;

#code with POSIX
my $days = floor((time()-$basetime) / 86400);

#code without POSIX
#my $days = sprintf("%d", (time()-$basetime) / 86400);

#code with Math::Round
#my $days = Math::Round::nearest_floor(1, (time()-$basetime) / 86400);

my $bigString = "We've been going for $days days.\n";

Win32::MsgBox($bigString);

现在，代码可以运行但会引发警告。其他两个 my $days 也没有发出警告。这是 POSIX 函数显示的警告。

Constant subroutine main::NULL redefined at C:/Strawberry/perl/lib/Exporter.pm line 66.
 at C:\coding\perl\posix-win32.pl line 3.
Prototype mismatch: sub main::NULL () vs none at C:/Strawberry/perl/lib/Exporter.pm line 66.
 at C:\coding\perl\posix-win32.pl line 3.

我认为我以前从未将 POSIX 与 Win32 结合使用，我可以看到它们都调用了一个类似命名的函数，空。但我不知道该怎么办。

我喜欢同时使用这两个模块，但显然，我不希望在更复杂的项目中出现这种情况。

抛出警告的原因是什么，我怎样才能简单地避免它？

Answer 1

你是对的，默认情况下，POSIX 和 Win32 都导出 NULL。

POSIX 是一个行为不佳的模块，默认情况下会导出太多太多(列表在底部)。考虑到这一点，只导入您需要的函数。

use Win32;
use POSIX qw(floor);

POSIX 使用 Exporter 来完成这个。参见 How To Import有关控制导入内容的更多详细信息。

$ perl -wle 'use POSIX; print join ", ", @POSIX::EXPORT'

isupper, isspace, fabs, F_GETLK, strncpy, EBADMSG, localeconv, SIGTRAP, ctermid, S_ISUID, fwrite, pow, strcoll, S_ISBLK, _POSIX_STREAM_MAX, EACCES, putc, FILENAME_MAX, tolower, sinh, EMLINK, ESOCKTNOSUPPORT, EDESTADDRREQ, DBL_MIN, fopen, TOSTOP, strncat, LINK_MAX, ENXIO, INLCR, TCION, NAME_MAX, EINPROGRESS, SIGILL, NDEBUG, VEOF, SEEK_END, ungetc, SEEK_CUR, STDOUT_FILENO, VEOL, ftell, UINT_MAX, ENOTEMPTY, DBL_EPSILON, INPCK, WIFSIGNALED, B134, remove, LC_TIME, SIGSEGV, _POSIX_PATH_MAX, F_RDLCK, SIG_BLOCK, VINTR, SA_NOCLDSTOP, PATH_MAX, isdigit, log10, O_RDWR, ENOTCONN, TMP_MAX, signal, F_SETLKW, qsort, O_TRUNC, _SC_TZNAME_MAX, _POSIX_NGROUPS_MAX, LC_COLLATE, _PC_NO_TRUNC, SCHAR_MAX, EHOSTUNREACH, fputs, ctime, fgetc, O_APPEND, _POSIX_ARG_MAX, EWOULDBLOCK, TCSAFLUSH, strstr, _exit, execle, malloc, DBL_MANT_DIG, _POSIX_SSIZE_MAX, puts, _SC_JOB_CONTROL, ttyname, B150, EMFILE, CS6, _POSIX_LINK_MAX, asin, mblen, _POSIX_PIPE_BUF, sigsuspend, B600, SIGPROF, L_ctermid, _SC_CLK_TCK, ceil, 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EXIT_FAILURE, clock, ENETDOWN, CS7, strrchr, SIGUSR2, tcdrain, INT_MIN, LDBL_DIG, _POSIX_JOB_CONTROL, SIG_UNBLOCK, _SC_STREAM_MAX, X_OK, F_UNLCK, ETIMEDOUT, CHAR_BIT, tmpnam, W_OK, sigpending, cfgetospeed, IEXTEN, geteuid, SIGRTMAX, E2BIG, LDBL_MIN, _SC_CHILD_MAX, CLK_TCK, NCCS, tzset, ENOMEM, gets, BRKINT, EDOM, ENODATA, ENOBUFS, ISTRIP, CLOCKS_PER_SEC, LDBL_MIN_EXP, SHRT_MIN, PARODD, EOF, asctime, ENFILE, EPROCLIM, freopen, sigaction, F_DUPFD, O_ACCMODE, FLT_MAX_10_EXP, difftime, TCOFLUSH, EINTR, ENOMSG, L_cuserid, B4800, EAGAIN, TCOON, setjmp, TZNAME_MAX, S_IWOTH, cuserid, PIPE_BUF, strtol, HUGE_VAL, F_GETFD, IGNPAR, EBUSY, memmove, ENOTBLK, getgid, SIGINT, EUSERS, SIGURG, EDEADLK, EOWNERDEAD, creat, _POSIX_MAX_CANON, _POSIX_CHOWN_RESTRICTED, execlp, F_SETFL, stdout, SIG_DFL, ldiv, SIGKILL, VSUSP, ENOTRECOVERABLE, B300, B200, HUPCL, WTERMSIG, offsetof, clearerr, tanh, getcwd, LDBL_MAX_10_EXP, SIG_SETMASK, ECHONL, O_NONBLOCK, S_IXOTH, ECONNABORTED, F_OK, tcflush, _POSIX_SAVED_IDS, 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_POSIX_OPEN_MAX, ESTALE, LC_CTYPE, S_ISREG, WIFEXITED, EPROTOTYPE, SIG_IGN, EIO, ENAMETOOLONG, EPERM, atoi, isgraph, ENOENT, errno, MAX_INPUT, setuid, _SC_OPEN_MAX, S_IRUSR, siglongjmp, getenv, CS8, EINVAL, NULL, ECHO, LDBL_EPSILON, SCHAR_MIN, ENETUNREACH, uname, DBL_MAX, ENOPROTOOPT, SIGSTOP, strtoul, SA_NODEFER, CREAD, SIGBUS, mbstowcs, EFBIG, cfsetispeed, ISIG, FLT_MIN, SA_NOCLDWAIT, fsync, LDBL_MAX_EXP, ENOTTY, VMIN, strtod, TCIFLUSH, SA_SIGINFO, fclose, strcspn, strpbrk, SIGTERM, ENOSTR, ULONG_MAX, LC_NUMERIC, scanf, getgroups, vfprintf, ENOSR, FLT_ROUNDS, EEXIST, S_IWGRP, ENOEXEC, SIGVTALRM, SIGPOLL, memcmp, atan, putchar, _POSIX_CHILD_MAX, fflush, fsetpos, WEXITSTATUS, atof, EFAULT, memchr, strcat, VSTOP, _POSIX_TZNAME_MAX, LDBL_MAX, strlen, setlocale, FLT_MIN_10_EXP, cosh, tcgetattr, realloc, div, CHAR_MAX, fprintf, UCHAR_MAX, execve, B75, ICRNL, strcpy, ECHOK, FD_CLOEXEC, cfgetispeed, iscntrl, strtok, SSIZE_MAX, SIGSYS, S_ISGID, strncmp, EISCONN, labs, CLOCAL, R_OK, memcpy, 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