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ERROR_UNDEFINED_CHARACTER
The character is undefined in the active Unicode data
ERROR_UNDEFINED_CHARACTER indicates that Windows cannot map or process a Unicode code point with the character data or conversion requested. The input can be structurally valid Unicode while still lacking a defined mapping in the target operation.
Where it can occur
- Converting Unicode text to a legacy code page that cannot represent the character.
- Using older system character tables with newer Unicode content.
- Requesting a normalization, collation, or glyph-related mapping that has no defined result.
- Processing reserved or unassigned code points.
Diagnosis
Record the code point, source and target encodings, Windows version, locale, and conversion flags. Distinguish an undefined character from a malformed surrogate sequence or missing font glyph.
Handling
Keep text in Unicode when possible. When conversion is unavoidable, choose a documented fallback such as replacement, escaping, or rejecting the value. Never drop characters silently in identifiers, paths, security labels, or user data.
Compatibility note
Unicode support evolves. Test with the oldest supported Windows version and avoid assuming that every newer assigned code point has a legacy-code-page representation.
References
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