Q: signed vs unsigned char, PPC vs x86 gcc 3.3.5 compiler differences

Q: signed vs unsigned char, PPC vs x86 gcc 3.3.5 compiler differences

[Bob Brose]

I'm trying to fix some of the AX25 code in the 2.6 kernel and traced down
a problem to the use of a char var which was being assigned
the value of -1. On x86 when the var was compared to -1 it succeded but
on PPC it failed. So I tried a simple test:

main()
{
char atest;
atest=-1;
printf("%i,%X\n",atest,atest);
}

With GCC 3.3.5 on 2.6.14-rc1 x86 I get:
./atest
-1,FFFFFFFF

With GCC 3.3.5 on 2.6.14-rc1 PPC I get:
./atest
255,FF

If I change the declaration of atest to a signed char on PPC I get the
same result as x86.

Does this mean the char in x86 is signed and in PPC it's unsigned?
Has it always been thus?
 

Re: Q: signed vs unsigned char, PPC vs x86 gcc 3.3.5 compiler differences

[Hollis Blanchard]

On Oct 2, 2005, at 9:11 PM, Bob Brose wrote:

> If I change the declaration of atest to a signed char on PPC I get the
> same result as x86.
>
> Does this mean the char in x86 is signed and in PPC it's unsigned?
> Has it always been thus?

Yes, and yes. If it matters to you, you should explicitly use "signed 
char" or "unsigned char"...

-Hollis

Re: Q: signed vs unsigned char, PPC vs x86 gcc 3.3.5 compiler differences

[Christopher Friesen]

Bob Brose wrote:

> Does this mean the char in x86 is signed and in PPC it's unsigned?
> Has it always been thus?

 From K+R:

"Whether plain chars are signed or unsigned is machine-dependent, but 
printable characters are always positive."

Chris