No-overflow cast on x64 - windows

Question

I have an existing C codebase that works on x86.
I'm now compiling it for x64.
What I'd like to do is cast a size_t to a DWORD, and throw an exception if there's a loss of data.
Q: Is there an idiom for this?
Here's why I'm doing this:
A bunch of Windows APIs accept DWORDs as arguments, and the code currently assumes sizeof(DWORD)==sizeof(size_t). That assumption holds for x86, but not for x64. So when compiling for x64, passing size_t in place of a DWORD argument, generates a compile-time warning.
In virtually all of these cases the actual size is not going to exceed 2^32. But I want to code it defensively and explicitly.
This is my first x64 project, so... be gentle.

Answer 1

see boost::numeric_cast
http://www.boost.org/doc/libs/1_33_1/libs/numeric/conversion/doc/numeric_cast.html

Answer 2

I just defined a function to perform the cast.
I included an assert-like behavior to insure I'm not silently rubbishing pointers.
DWORD ConvertSizeTo32bits(size_t sz, char *file, int line)
{
if (!(0 <= sz && sz <= INT32_MAX)) {
EmitLogMessage("Invalid Pointer size: %d file(%s) line(%d)",
sz, file, line);
ExitProcess( 0 );
}
return (DWORD) sz;
}

Answer 3

#define size_t_to_DWORD(st,dw) if ((DWORD)(st) != st) RaiseException(exLossOfData, 0, 0, NULL); else dw = (DWORD)(st)
size_t st;
DWORD dw;
st = 0xffffffff;
size_t_to_DWORD(st,dw); // this succeeds
st = 0xffffffff1;
size_t_to_DWORD(st,dw); // this throws
EDIT:
Or better yet, do this so you can use it in an expression:
DWORD MyRaiseException()
{
RaiseException(1, 0, 0, NULL);
return 0;
}
#define size_t_to_DWORD(st) (DWORD)(st) != (st) ? MyRaiseException() : (DWORD)(st)
void main(void)
{
size_t st;
DWORD dw;
st = 0xffffffff1;
dw = size_t_to_DWORD(st);
printf("%u %u\n", st, dw);
}