Compiler warning due to different string alignments in mqueue.cpp code

[oPaveo]

I use Visual Studio 2017 (msvc15) under Windows 10 and Crypto++ 6.10.
I get the following linker warning:

Warning C4742: '`string'' has different alignment in '\cryptopp\mqueue.cpp' and 'foo\bar.cpp': 1 and 2

I know that is the Microsoft compiler problem and I reported it to them.
But I also know why It occures and there is a very simple way to avoid it.

In your code, in mqueue.cpp we have

return Output(1, (const byte *)"\0", 1, 0, blocking) != 0;

The string "\0" is actually a two-element array of two zero bytes - exactly the same as L"". So the problem is whether it is a 1-length char* or an empty wide string.

Maybe you can write
return Output(1, (const byte *)"\0\0", 1, 0, blocking) != 0;
or
return Output(1, (const byte *)"", 1, 0, blocking) != 0;

Both codes works the same way and without linker warnings.

P.S. Older versions of Crypto++ give the same effect, of course.

[noloader]

Thanks @oPaveo.

Yeah, we want to be as warning free as possible. That warning should be contained. It's a bug on our part.

It looks like you are taking about this function:

bool EqualityComparisonFilter::HandleMismatchDetected(bool blocking)
{
	m_mismatchDetected = true;
	if (m_throwIfNotEqual)
		throw MismatchDetected();
	return Output(1, (const byte *)"\0", 1, 0, blocking) != 0;
}

And Output from filters.h

size_t Output(int outputSite, const byte *inString, size_t length, int messageEnd, bool blocking, const std::string &channel=DEFAULT_CHANNEL);

How do you feel about doing away with the string literal altogether. Maybe something like:

bool EqualityComparisonFilter::HandleMismatchDetected(bool blocking)
{
	m_mismatchDetected = true;
	if (m_throwIfNotEqual)
		throw MismatchDetected();

        // https://github.com/weidai11/cryptopp/issues/591
        const byte b[1] = {0};
	return Output(1, b, 1, 0, blocking) != 0;
}

[oPaveo]

Hello,
Your solution looks very well. I tested it in my environment and it is also warning free :-)
Thanks.

[noloader]

Thanks @oPaveo,

Do you want to make a PR, or would you like us to handle it?

[oPaveo]

I prefer to leave it to you.

[noloader]

Thanks again @oPaveo.

Cleared at Commit 53ccd310b8b3.