Padding bits and char, unsigned char, signed char

[Ioannis Vranos]

Under C95:

Is it guaranteed that char, unsigned char, signed char have no padding bits?

[CBFalconer]

Re: Padding bits and char, unsigned char, signed char

Ioannis Vranos wrote:

>
Under C95: Is it guaranteed that char, unsigned char, signed
char have no padding bits?

unsigned char, yes. The others by implication. I haven't checked
the standard. Why don't you?

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[Harald van =?UTF-8?b?RMSzaw==?=]

Re: Padding bits and char, unsigned char, signed char

On Fri, 28 Mar 2008 16:01:54 -0500, CBFalconer wrote:

Ioannis Vranos wrote:

>Under C95: Is it guaranteed that char, unsigned char, signed char have
>no padding bits?

Just a note: padding bits are a concept introduced in the standard in
C99; C90/C95 left much more unspecified about the representation of
integer types.

unsigned char, yes.

Where is this guarantee made? In C99, 5.2.4.2.1 makes it as clear as it
can: "The value UCHAR_MAX shall equal 2^CHAR_BIT - 1." I don't have a
copy of an older standard. Does it make the same guarantee?

The others by implication.

How so? What's preventing a signed integer type and its corresponding
unsigned type from having a different number of padding bits?

[pete]

Re: Padding bits and char, unsigned char, signed char

Harald van =?UTF-8?b?RMSzaw==?= wrote:

>
On Fri, 28 Mar 2008 16:01:54 -0500, CBFalconer wrote:

Ioannis Vranos wrote:

Under C95: Is it guaranteed that char,
unsigned char, signed char have no padding bits?

>
Just a note: padding bits are a concept introduced in the standard in
C99; C90/C95 left much more unspecified about the representation of
integer types.
>

unsigned char, yes.

>
Where is this guarantee made?
In C99, 5.2.4.2.1 makes it as clear as it
can: "The value UCHAR_MAX shall equal 2^CHAR_BIT - 1." I don't have a
copy of an older standard. Does it make the same guarantee?

It doesn't.
There's really nothing about padding in the "basic types" in C90.

The others by implication.

>
How so? What's preventing a signed integer type and its corresponding
unsigned type from having a different number of padding bits?

I think he meant char and signed char, but even then I disagree.

As far as I know, signed char can have padding bits.

--
pete

[Ben Bacarisse]

Re: Padding bits and char, unsigned char, signed char

Harald van Dijk <truedfx@gmail. comwrites:

On Fri, 28 Mar 2008 16:01:54 -0500, CBFalconer wrote:

>Ioannis Vranos wrote:

>>Under C95: Is it guaranteed that char, unsigned char, signed char have
>>no padding bits?

>
Just a note: padding bits are a concept introduced in the standard in
C99; C90/C95 left much more unspecified about the representation of
integer types.
>

>unsigned char, yes.

>
Where is this guarantee made? In C99, 5.2.4.2.1 makes it as clear as it
can: "The value UCHAR_MAX shall equal 2^CHAR_BIT - 1."

But that alone is not enough, is it? The clearest statement comes
later in 6.2.6. p1: "For unsigned integer types other than unsigned
char, the bits of the object representation shall be divided into two
groups: value bits and padding bits (there need not be any of the
latter).". So, unsigned char has only value bits.

--
Ben.