I use mb_convert_encoding function to convert UTF8 characters to SJIS characters.
Before conversion:でんぱ組 出会いの歌26 カミソヤマ ユニ
After conversion: て?んは?組 出会いの歌26 カミソヤマ ユニ
Non-convertible characters: て?んは?
Code used to convert :
$str = mb_convert_encoding('でんぱ組 出会いの歌26 カミソヤマ ユニ', "SJIS", "UTF-8");
で as 1 grapheme is only a rendering of composing the 2 Unicode codepoints て and ◌゙ (not to be confused with the codepoint ゛ that can't be combined) - the former can be translated from UTF-8 to Shift-JIS, the latter not.
Same thing with: ぱ - it's combined from は and ◌゚ instead of being one single character:
| で | て | ◌゙ | ぱ | は | ◌゚ | |
|---|---|---|---|---|---|---|
| Unicode | U+3066 | U+3067 | U+3099 | U+3071 | U+306F | U+309A |
| UTF-8 | e3 81 a6 |
e3 81 a6 |
e3 82 99 |
e3 81 b1 |
e3 81 af |
e3 82 9a |
| Shift-JIS or CP932 |
82 c5 |
82 c4 |
(doesn't exist) | 82 cf |
82 cd |
(doesn't exist) |
Just because you see 1 grapheme (f.e. で or ぱ) in Unicode (f.e. in UTF-8) it doesn't mean it is build from 1 codepoint. You can neither trust your eyes, nor your user's input - it can either be really 1 codepoint or not. You have to normalize your UTF-8 text (f.e. to the NFC form) before converting it to Shift-JIS, as then those 2 codepoints (U+3067 and U+3099) for 1 grapheme also become 1 codepoint (U+3066), which can then also be translated to Shift-JIS without problems (82 c5).
In PHP the extension intl must be installed, then you can use normalizer_normalize() - the result of that function can then be fully converted to Shift-JIS.
