Re: Incorrect compiler warning C4267

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

microsoft.public.vc.stl

Date:

Fri, 09 Feb 2007 09:33:05 +0100

Message-ID:

<37ot94-3pr.ln1@satorlaser.homedns.org>

Number 774 wrote:

I'm running VS 2005, configured for 32 bit with 64 bit warnings on. This
bit of code

#include <vector>
#include <list>
std::vector<size_t> vs;
std::list<unsigned int> uiList;
unsigned int ui = uiList.front();

results in a compiler warning at the last line
warning C4267: 'initializing' : conversion from 'size_t' to 'unsigned
int', possible loss of data uiList.front()'s data type should be
reference to unsigned int, so it ought to compile fine.

Following problem: size_t and unsigned int are the same types as far as C++
is concerned. MS' compiler attaches to the size_t typedef the additional
information that it might be 64 bits, which it doesn't attach to unsigned
int (I'm just starting to wonder why size_t isn't unsigned long
instead...?). Now, vector<size_t> instantiates other types like e.g.
allocator<size_t> which is identical to allocator<unsigned int>. When using
the same allocator as allocator<unsigned int> the compiler uses
allocator<size_t> with the additional info that it might be 64 bits still
attached, ergo your bogus compiler warning.

Disclaimer: I'm only guessing how the compiler works, I don't have the
sources at hand to check.

I reckon this is a compiler bug.

Yep, though it isn't likely to cause any severe misbehaviour.

Uli