Re: C4267 with std::deque<size_t>
- From: "Alex Blekhman" <xfkt@xxxxxxxxx>
- Date: Sun, 23 Jul 2006 12:59:24 +0300
<gast128@xxxxxxxxxxx> wrote:
Dear all,
we have encountered a very strange warning in a very
specific contex:
using a std::deque with size_t on VStudio 2003, warning
level 4 and an
exported bool vector, i.e.:
//1.cpp
#include <deque>
#define CLASS_EXPORT __declspec(dllexport)
//for explicit (DLL) instantiation of vector's:
#pragma warning(push)
#pragma warning(disable: 4251)
//warning C4251: ... needs to have dll-interface to be
used by clients,
(TODO: can be dangerous however)
#include <vector>
#pragma warning(pop)
//explicit (DLL) instantiation
template class CLASS_EXPORT std::vector<bool>;
int main()
{
//std::deque<unsigned> tmp1;
std::deque<size_t> tmp;
tmp.resize(3);
return 0;
}
A compiler bug I presume?
Not exactly. I'd call it compiler peculiarity. I can
reproduce it with VC2005, as well. Explicit instantiation of
std::vector<bool> is enough to trigger the C4267 warning. I
don't know why instantiation of std::vector<bool> triggered
this, however I have explanation to C4267 warning.
C4267 warns that `size_t' being converted to `unsigned int'.
It's 64-bit compatibility warning. Under 64-bit Windows
`size_t' is 64 bits while `unsigned int' is still 32 bits.
However, under 32-bit Windows `size_t' is typedef'ed as
`unsigned int'. I think that when std::deque<size_t> is
instantiated, then it happens in two stages (or more) where
one stage already recognizes `size_t' as `unsigned int',
while other still sees `size_t'. So, in one place it's
already `unsigned int' and in the other it's `size_t'.
Compiler cannot predict that in all places it will become
appropriate size type eventually, hence it warns.
As a quick solution you can disable Win64 portability issues
detection (/Wp64 flag) for the project. Alternatively you
can disable C4267 warning explicitly:
#pragma warning(disable: 4267)
#include <vector>
#pragma warning(default: 4267)
HTH
Alex
.
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