PATH Mac OS 8 and 9 Developer Documentation > Text Encoding Conversion Manager
Programming With the Text Encoding Conversion Manager

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Setting the Fallback Handler

A fallback handler is a function that the Unicode Converter uses to perform fallback mapping from Unicode to another encoding. Fallback mapping is invoked if the kUnicodeUseFallbacksMask control flag is set and the converter encounters a Unicode character that cannot be mapped to the destination encoding using either strict mappings or--if the kUnicodeLooseMappingsMask control flag is set--loose mappings.

Fallback mapping from Unicode is a process in which a Unicode character is mapped to a sequence of one or more characters in another encoding that may not have the same meaning or use, but that may provide an approximate graphic representation or even textual representation of the corresponding Unicode character. The fallback mapping depends on the destination encoding. In general, fallback mappings are not reversible, and therefore, do not provide round-trip fidelity.

The Unicode Converter supplies a default fallback handler for mapping from Unicode to other encodings. Using SetFallbackUnicodeToText or SetFallbackUnicodeToTextRun, you can also install your own application-defined fallback handler and use it alone, or you can use yours in combination with the default fallback handler. If you use both, you can specify which one gets called first; the other one gets called only if the first one fails. If fallback mapping is invoked and the specified fallback handler fails--or if both handlers fail when both are used--then the Unicode Converter uses a default fallback sequence obtained from the mapping table to represent the unmappable Unicode character. The default fallback sequence is usually a question mark character in the destination encoding.

SetFallbackUnicodeToText

SetFallbackUnicodeToTextRun