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From: tim todd on 18 Jun 2008 10:57
how do i do this correctly without warnings?

char buf[10];
buf[0] = (char)254;

if I say static_cast<char>(254) I get warnings

warning C4305: '=' : truncation from 'int' to 'char'
warning C4309: '=' : truncation of constant value

Thanks!
Todd.


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From: Martin T. on 18 Jun 2008 15:39
tim todd wrote:
> how do i do this correctly without warnings?
>
> char buf[10];
> buf[0] = (char)254;
>
> if I say static_cast<char>(254) I get warnings
>
> warning C4305: '=' : truncation from 'int' to 'char'
> warning C4309: '=' : truncation of constant value
>

The reason is that char is a signed type going from -128 to 127 and
cannot hold 254. You may want to try unsigned char.

br,
Martin

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From: Ulrich Eckhardt on 18 Jun 2008 15:39
tim todd wrote:
> how do i do this correctly without warnings?
>
> char buf[10];
> buf[0] = (char)254;

First of all, please forget about the fact that these C-style casts exist in
C++ for now. These rarely even help except to shift compiler errors or
warnings to runtime misbehaviour. Just don't use them.

> if I say static_cast<char>(254) I get warnings
>
> warning C4305: '=' : truncation from 'int' to 'char'
> warning C4309: '=' : truncation of constant value

The problem is that a 'char' can't hold a value of 254, simple as that. I
guess the range of 'char' on your system is -128 to 127.

The question now is not how to get 254 into that, but rather what you want
to express and then chose the right type and not 'char'. My guess is that
you want to express a byte-buffer, for which 'unsigned char' would be much
better.

Uli


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From: Ulrich Eckhardt on 19 Jun 2008 07:01
Martin T. wrote:
> char is a signed type

No, whether char is signed is implementation defined and systems where it is
unsigned are even common, PowerPC platforms, for example.

Uli

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From: Martin Bonner on 19 Jun 2008 07:08
On Jun 19, 7:39 am, "Martin T." <0xCDCDC...(a)gmx.at> wrote:
> tim todd wrote:
> > how do i do this correctly without warnings?
>
> > char buf[10];
> > buf[0] = (char)254;
>
> > if I say static_cast<char>(254) I get warnings
>
> > warning C4305: '=' : truncation from 'int' to 'char'
> > warning C4309: '=' : truncation of constant value
>
> The reason is that char is a signed type going from -128 to 127
s/is/may be/
An implementation is at liberty to have 'char' be an unsigned type.

> and cannot hold 254.
.... on the OP's platform.

> You may want to try unsigned char.
Absolutely.

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