Encodes c as UTF-8 starting at ptr + index, returning the number of bytes written (1–4).

Companion of decodeUtf8. c.utf8Length() predicts the same byte count without writing — call it first to ensure the buffer has room.

Safety

ptr + index through ptr + index + utf8Length() - 1 must lie within an allocated, writable region. No bounds checking happens here.

Examples

// Conceptually, given a buffer `buf` of length 4: // encodeUtf8('a', buf, at: 0); // 1 // encodeUtf8('\u{1F600}', buf, at: 0); // 4