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From: Howard Hinnant (hinnant_at_[hidden])
Date: 2005-07-23 17:54:18

On Jul 23, 2005, at 1:48 PM, Slawomir Lisznianski wrote:

> Hello,
> I'm looking for a way to convert an integral type into its unsigned
> equivalent. For example, assume a trait called to_unsigned_integral
> such
> that:
> to_unsigned_integral<int>::type ---> yields unsigned int
> to_unsigned_integral<short>::type ---> yields unsigned short
> to_unsigned_integral<unsigned char>::type ---> yields unsigned char
> ...

template <class T> struct to_unsigned_integral
     {typedef T type;};
template <> struct to_unsigned_integral<char>
     {typedef unsigned char type;};
template <> struct to_unsigned_integral<signed char>
     {typedef unsigned char type;};
template <> struct to_unsigned_integral<short>
     {typedef unsigned short type;};
template <> struct to_unsigned_integral<int>
     {typedef unsigned int type;};
template <> struct to_unsigned_integral<long>
     {typedef unsigned long type;};
template <> struct to_unsigned_integral<long long>
     {typedef unsigned long long type;};

I've found it pretty useful myself too. :-)

If you're paranoid about non-integral types you could dress up the
primary template a little to return T only for integral types, and void
otherwise (or static_assert). But in practice I haven't come across
the need to go to that trouble.

This tool comes in very handy when doing bit manipulations on generic
types, e.g.:

template <class T>
rotate_left(T x, int n = 1);

(bit manipulations are more portable if you traffic in unsigned types)


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