The Wikipedia page for the encoding does hint at the underlying problem. Quote: "ISO/IEC 6937 does not encode any combining characters whatsoever". So formally the .NET encoder does what the standard says, practically it is not useful.
This can be done better than the linked GitHub code, the much cleaner approach is to make your own Encoding class. About all of the work can be delegated to the .NET encoding, you just have to intercept the diacritics. Which requires using the combining mark and swapping it with the letter. Like this:
class ISO6937Encoding : Encoding {
private Encoding enc = Encoding.GetEncoding(20269);
public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex) {
int cnt = enc.GetChars(bytes, byteIndex, byteCount, chars, charIndex);
for (int ix = 0; ix < byteCount; ix++, charIndex++) {
int bx = byteIndex + ix;
if (bytes[bx] >= 0xc1 && bytes[bx] <= 0xcf) {
if (charIndex == chars.Length - 1) chars[charIndex] = '?';
else {
const string subst = "\u0300\u0301\u0302\u0303\u0304\u0306\u0307\u0308?\u030a\u0337?\u030b\u0328\u030c";
chars[charIndex] = chars[charIndex + 1];
chars[charIndex + 1] = subst[bytes[bx] - 0xc1];
++ix;
++charIndex;
}
}
}
return cnt;
}
// Rest is boilerplate
public override int GetByteCount(char[] chars, int index, int count) {
return enc.GetByteCount(chars, index, count);
}
public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex) {
return enc.GetBytes(chars, charIndex, charCount, bytes, byteIndex);
}
public override int GetCharCount(byte[] bytes, int index, int count) {
return enc.GetCharCount(bytes, index, count);
}
public override int GetMaxByteCount(int charCount) {
return enc.GetMaxByteCount(charCount);
}
public override int GetMaxCharCount(int byteCount) {
return enc.GetMaxCharCount(byteCount);
}
}
Not extensively tested.
