来自编码函数的检查参数

Question

为什么我从第二个循环（CHECK 参数集）得到不同的输出？

#!/usr/bin/env perl
use warnings;
use 5.012;
use Encode qw(encode);
my $s = 'a';

for my $encoding ( 'iso-8859-1', 'iso-8859-15', 'cp1252', 'cp850' ) {
    my $encoded = encode( $encoding, $s );
    my $c = unpack '(B8)*', $encoded;
    printf "%-12s:\t%8s\n", $encoding, $c;
}

say "-------------------";

for my $encoding ( 'iso-8859-1', 'iso-8859-15', 'cp1252', 'cp850' ) {
    my $encoded = encode( $encoding, $s, Encode::FB_WARN );
    my $c = unpack '(B8)*', $encoded;
    printf "%-12s:\t%8s\n", $encoding, $c;
}


# iso-8859-1  :   01100001
# iso-8859-15 :   01100001
# cp1252      :   01100001
# cp850       :   01100001
# -------------------
# iso-8859-1  :   01100001
# Use of uninitialized value $c in printf at ./perl1.pl line 20.
# iso-8859-15 :           
# Use of uninitialized value $c in printf at ./perl1.pl line 20.
# cp1252      :           
# Use of uninitialized value $c in printf at ./perl1.pl line 20.
# cp850       :   

Answer 1

文档中描述了该行为（请参阅下面的片段） - 它修改数据并将未处理的部分留在$s中。由于没有错误，它基本上清除了你的变量。

*CHECK* = Encode::FB_QUIET
  If *CHECK* is set to Encode::FB_QUIET, (en|de)code will immediately
  return the portion of the data that has been processed so far when an
  error occurs. The data argument will be overwritten with everything
  after that point (that is, the unprocessed part of data). This is
  handy when you have to call decode repeatedly in the case where your
  source data may contain partial multi-byte character sequences, (i.e.
  you are reading with a fixed-width buffer). Here is a sample code that
  does exactly this:

    my $buffer = ''; my $string = '';
    while(read $fh, $buffer, 256, length($buffer)){
      $string .= decode($encoding, $buffer, Encode::FB_QUIET);
      # $buffer now contains the unprocessed partial character
    }

*CHECK* = Encode::FB_WARN
  This is the same as above, except that it warns on error. Handy when
  you are debugging the mode above.

Answer 2

当 CHECK 设置为 Encode::FB_QUIET 时，数据参数将被覆盖：

perl -MEncode -Mutf8 -E '$s="a"; encode("utf-8", $s, Encode::FB_WARN); say $s'

Answer 3

您可以通过 Encode::LEAVE_SRC 中的 or 来防止覆盖

my $encoded = encode( $encoding, $s, Encode::FB_WARN | Encode::LEAVE_SRC);