template string_type make_unique_string_nothrow()

in include/wil/resource.h [3271:3318]

• 40 lines of code
• 11 McCabe index (conditional complexity)

    template<typename string_type> string_type make_unique_string_nothrow(
        _When_((source != nullptr) && length != static_cast<size_t>(-1), _In_reads_(length))
        _When_((source != nullptr) && length == static_cast<size_t>(-1), _In_z_)
        const wchar_t* source, size_t length = static_cast<size_t>(-1)) WI_NOEXCEPT
    {
        // guard against invalid parameters (null source with -1 length)
        FAIL_FAST_IF(!source && (length == static_cast<size_t>(-1)));

        // When the source string exists, calculate the number of characters to copy up to either
        // 1) the length that is given
        // 2) the length of the source string. When the source does not exist, use the given length
        //    for calculating both the size of allocated buffer and the number of characters to copy.
        size_t lengthToCopy = length;
        if (source)
        {
            size_t maxLength = length < MAKE_UNIQUE_STRING_MAX_CCH ? length : MAKE_UNIQUE_STRING_MAX_CCH;
            PCWSTR endOfSource = source;
            while (maxLength && (*endOfSource != L'\0'))
            {
                endOfSource++;
                maxLength--;
            }
            lengthToCopy = endOfSource - source;
        }

        if (length == static_cast<size_t>(-1))
        {
            length = lengthToCopy;
        }
        const size_t allocatedBytes = (length + 1) * sizeof(*source);
        auto result = static_cast<PWSTR>(details::string_allocator<string_type>::allocate(allocatedBytes));

        if (result)
        {
            if (source)
            {
                const size_t bytesToCopy = lengthToCopy * sizeof(*source);
                memcpy_s(result, allocatedBytes, source, bytesToCopy);
                result[lengthToCopy] = L'\0'; // ensure the copied string is zero terminated
            }
            else
            {
                *result = L'\0'; // ensure null terminated in the "reserve space" use case.
            }
            result[length] = L'\0'; // ensure the final char of the buffer is zero terminated
        }
        return string_type(result);
    }