StringEncodingConverter

1

Can someone explain the safety of this magic? It terrifies me but I can’t sort of see how it might work. What happens if you use two encoding converters on the same const String & s in the same function call - unlikely but this will explode right?

template <class CharPointerType_Src, class CharPointerType_Dest>
struct StringEncodingConverter
{
    static CharPointerType_Dest convert (const String& s)
    {
        auto& source = const_cast<String&> (s);

        using DestChar = typename CharPointerType_Dest::CharType;

        if (source.isEmpty())
            return CharPointerType_Dest (reinterpret_cast<const DestChar*> (&emptyChar));

        CharPointerType_Src text (source.getCharPointer());
        auto extraBytesNeeded = CharPointerType_Dest::getBytesRequiredFor (text) + sizeof (typename CharPointerType_Dest::CharType);
        auto endOffset = (text.sizeInBytes() + 3) & ~3u; // the new string must be word-aligned or many Windows
                                                         // functions will fail to read it correctly!
        source.preallocateBytes (endOffset + extraBytesNeeded);
        text = source.getCharPointer();

        void* const newSpace = addBytesToPointer (text.getAddress(), (int) endOffset);
        const CharPointerType_Dest extraSpace (static_cast<DestChar*> (newSpace));

       #if JUCE_DEBUG // (This just avoids spurious warnings from valgrind about the uninitialised bytes at the end of the buffer..)
        auto bytesToClear = (size_t) jmin ((int) extraBytesNeeded, 4);
        zeromem (addBytesToPointer (newSpace, extraBytesNeeded - bytesToClear), bytesToClear);
       #endif

        CharPointerType_Dest (extraSpace).writeAll (text);
        return extraSpace;
    }
};
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