U+00A5 & U+203E to CP932, with or without 'best fit' mapping

001_testWideCharToMultiByte.php

<?php

declare(strict_types=1);

const WC_NO_BEST_FIT_CHARS = 0x00000400;

function test(string $utf8_str, bool $best_fit): void {
    $ffi = \FFI::cdef(<<<CDECLS
        int WideCharToMultiByte(
            unsigned int CodePage,
            unsigned long dwFlags,
            const char *lpWideCharStr,
            int cchWideChar,
            char *lpMultiByteStr,
            int cbMultiByte,
            const char *lpDefaultChar,
            int *pfUsedDefaultChar
        );
        CDECLS,
        'Kernel32.dll'
    );

    $test = mb_convert_encoding($utf8_str, 'UTF-16LE', 'UTF-8') . "\0";
    $buffer = \FFI::new('char[2]');
    $usedDefault = \FFI::new('int');

    $ffi->WideCharToMultiByte(
        932,
        $best_fit ? 0 : WC_NO_BEST_FIT_CHARS,
        $test,
        -1,
        $buffer,
        2,
        null,
        \FFI::addr($usedDefault)
    );

    var_dump(
        sprintf('%02x', \ord($buffer[0])),
        sprintf('%02x', \ord($buffer[1])),
        $usedDefault
    );
}

test("\u{00A5}", true);
test("\u{00A5}", false);
test("\u{203E}", true);
test("\u{203E}", false);

002_output,txt

string(2) "5c"
string(2) "00"
object(FFI\CData:int32_t)#3 (1) {
  ["cdata"]=>
  int(0)
}
string(2) "3f"
string(2) "00"
object(FFI\CData:int32_t)#1 (1) {
  ["cdata"]=>
  int(1)
}
string(2) "3f"
string(2) "00"
object(FFI\CData:int32_t)#3 (1) {
  ["cdata"]=>
  int(1)
}
string(2) "3f"
string(2) "00"
object(FFI\CData:int32_t)#1 (1) {
  ["cdata"]=>
  int(1)
}