[patch] proposed fix for libstdc++/59829

[Marc Glisse]

On Mon, 27 Jan 2014, Jonathan Wakely wrote:

> This is the best I've come up with to avoid dereferencing an invalid
> pointer when calling vector::data() on an empty vector.
>
> For C++03 we reurn the vector's pointer type, so can just return the
> internal pointer, but for C++11 we need to convert that to a raw
> pointer, which we do by dereferencing, so we must check if it's valid
> first.

For comparison, libc++ has 2 paths. If pointer really is a pointer, it 
just returns it, no need to pay for a comparison in that case. And 
otherwise, it calls _M_start.operator-> and crosses its fingers. There is 
a helper function doing that used throughout the library.

-- 
Marc Glisse