std::to_string fixed in Visual Studio 2012

Among many other fixes coming in the new version of Visual Studio, is a fix to std::to_string (introduced in Visual Studio 2010) providing the full range of numerical types. Currently using the function with any numerical type other than long long or long double or unsigned long long yields compiler error C2668 – ambiguous call to overloaded function.

Whilst annoying, there’s a trivial workaround for Visual Studio 2010 to still use this handy function without resorting to boost::lexical_cast by static_casting to one of the three currently provided overloads. As of VS 2012, such massaging of types is no longer required. 🙂

Silent promotions

A few days ago I came across a bit of nasty behaviour when evaluating an expression performing a simple calculation on a signed and unsigned integer. Take the following C++ code snippet:

unsigned int nA = 10;
int nB = 11;

if( nA – nB < 0 )
{
// etc…
}

On first inspection, given the inputs I would expect the expression to evaluate to true. What surprised me is that, despite no compiler warnings being emitted using Visual Studio 2010 at warning level 4, the statement evaluates to false.

It turns out the signed int is silently promoted to an unsigned int which changes things. The answer to 10 – 11 is no longer -1 but 4294967294 ( or UINT_MAX-1 ) since an unsigned integer can’t hold a negative number (no ‘spare’, top bit for sign indication) and has wrapped around.

There are a few different fixes depending on the what your function is trying to do. Assuming mixing signed and unsigned types is unavoidable, the following fix to this is simple assuming there can be no range violations and you won’t end up with a large negative number for the left hand side:

if( static_cast( nA ) – nB < 0 )

I understand that gcc does emit a warning about this with -Wextra but the usual advice of test test test is hard to beat. Did I mention that I’m a huge fan of unit tests?

The Pi has landed

So my Raspberry Pi finally arrived today! Despite the launch morning kerfuffle I somehow (it’s still a mystery to me exactly how) managed to bag one from the first batch.

Here it is pictured alongside an Arduino for size reference – it’s slightly bigger but not by much. When I’ve had time to really explore what it is capable of I’ll write some more on the subject.