On Oct 16, 2014, at 4:50 AM, Graham Bloice <graham.blo...@trihedral.com> wrote:

> Visual Studio (VS2013 at least) as 32 & 64 bit ARM compilers.

        http://msdn.microsoft.com/en-us/library/0w6ke344.aspx

"Type char

Visual Studio 2013      Other Versions          1 out of 1 rated this helpful - 
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The char type is used to store the integer value of a member of the 
representable character set. That integer value is the ASCII code corresponding 
to the specified character.

Microsoft Specific

Character values of type unsigned char have a range from 0 to 0xFF hexadecimal. 
A signed char has range 0x80 to 0x7F. These ranges translate to 0 to 255 
decimal, and –128 to +127 decimal, respectively. *The /J compiler option 
changes the default from signed to unsigned.*

END Microsoft Specific"

(emphasis mine, as that seems to implicitly indicate that an unqualified "char" 
is signed by default).

So, unless that page discusses *only* the 
x86-32/x86-64/Itanium-if-they-still-support-it compilers, it appears that char 
is signed by default on all platforms, presumably including ARM.

What we *could* do is, on some platform or platforms, do both default compiles 
and char-is-unsigned compiles, using /J for MSVC and -funsigned-char with GCC 
(and Clang?).

(I couldn't find any -W option for GCC that warns about code that would behave 
differently with char-is-signed and char-is-unsigned. There should be, but, 
then, there should also be an option to warn about *all* implicit shortenings - 
or, at least, all implicit shortenings that aren't known to be safe, such as 
converting "sizeof (int)" to a type shorter than size_t - even though there 
should be.)
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