Windows provides encoding conversion functions (“MultiByteToWideChar” and “WideCharToMultiByte”) which are capable of UTF-8 to/from UTF-16 conversions, among other things. But I’ve seen people offer home-grown 30 to 40 line functions that claim also to perform UTF-8 / UTF-16 encoding conversions.
My question is, how reliable are such tiny converters? Can such a tiny amount of code handle problems such as converting a UTF-16 surrogate pair (such as <D800 DC00>) into a UTF-8 single four byte sequence (rather than making the mistake of converting into a pair of three byte sequences)? Can they correctly spot “unpaired” surrogate input, and provide an error?
In short, are such tiny converters mere toys, or can they be taken seriously? For that matter, why does unicode.org seemingly offer no advice on an algorithm for accomplishing such conversions?
The open source ICU library has 113 lines of code for ucnv_fromUnicode_UTF8 (source/common/ucnv_u8.c). Error checking included, proper surrogate handling, some comments. You should only consider using something else if you don’t like the naming conventions.