Signed & unsigned types

[Ido Yehieli]

Hi,
from what i've read (http://tigcc.ticalc.org/doc/
keywords.html#short) and unsigned int should normally be in the range
0 to 65535. However, compiling and running this program:

#include <stdio.h>

int main(){
unsigned int y=1;
y-=2;
printf("y=%i\n",y);
}

produces "y=-1". shouldn't it be either 65535 or some error?

-ido.

[Chris Dollin]

Ido Yehieli wrote:

Hi,
from what i've read (http://tigcc.ticalc.org/doc/
keywords.html#short) and unsigned int should normally be in the range
0 to 65535.

No, it should normally be in the range that the implementation specifies.
Not all implementations have 16-bit [[un]signed] ints.

However, compiling and running this program:

#include <stdio.h>

int main(){
unsigned int y=1;
y-=2;
printf("y=%i\n",y);
}

produces "y=-1". shouldn't it be either 65535 or some error?

Shouldn't you use an unsigned format to print an unsigned integer?

--
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Hewlett-Packard Limited Cain Road, Bracknell, registered no:
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[Mark Bluemel]

Ido Yehieli wrote:

Hi,
from what i've read (http://tigcc.ticalc.org/doc/
keywords.html#short) and unsigned int should normally be in the range
0 to 65535. However, compiling and running this program:

#include <stdio.h>

int main(){
unsigned int y=1;
y-=2;
printf("y=%i\n",y);

What does the %i mask in printf() expect?

What mask should you specify for unsigned data?

}

produces "y=-1". shouldn't it be either 65535 or some error?

You lied to printf(), by saying you were providing an "int" argument,
but actually providing an "unsigned int". You get undefined behaviour.

Some compilers may give you a warning, but you can't rely on that.

[Ido Yehieli]

On Dec 5, 11:25 am, Chris Dollin <[e-mail]:

Shouldn't you use an unsigned format to print an unsigned integer?

Oh right... thanks.

[Ido Yehieli]

On Dec 5, 11:31 am, Mark Bluemel <[e-mail]:

Some compilers may give you a warning, but you can't rely on that.

Do you know of a compiler that does strict type checking?
So that the code above would produce 2 errors or warnings, one for the
%i and one for making an unsigned int negative?

-ido.

[Mark Bluemel]

Ido Yehieli wrote:

On Dec 5, 11:31 am, Mark Bluemel <[e-mail]:

>Some compilers may give you a warning, but you can't rely on that.

Do you know of a compiler that does strict type checking?
So that the code above would produce 2 errors or warnings, one for the
%i and one for making an unsigned int negative?

No I don't. GCC is, to some extent, capable of checking printf usage
but it didn't complain about your source.

[CBFalconer]

Ido Yehieli wrote:

Mark Bluemel <[e-mail]:

>Some compilers may give you a warning, but you can't rely on that.

Do you know of a compiler that does strict type checking?
So that the code above would produce 2 errors or warnings, one for
the %i and one for making an unsigned int negative?

What 'code above'? See my sig.

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[Peter Nilsson]

Ido Yehieli <[e-mail]:

I guess what i should do is to use a signed int and
add something like:

assert(int_that_should_be_positive>-1);

Not if int_that_should_be_positive is an unsigned int or
higher. In a comparison of unsigned int and int values,
the int (in this case -1) will be converted to an unsigned
int.

Some compilers will actually warn you that the condition
may always be false in that particular case!

If you want to test for non-negative integers, use...

int_that_should_be_positive >= 0

Again, you may get a warning that this condition is always
true for unsigned integer types, but you can ignore that
warning.

--
Peter

[Jack Klein]

On Wed, 05 Dec 2007 10:31:46 +0000, Mark Bluemel
<ma**********@pobox.comwrote in comp.lang.c:

Ido Yehieli wrote:

Hi,
from what i've read (http://tigcc.ticalc.org/doc/
keywords.html#short) and unsigned int should normally be in the range
0 to 65535. However, compiling and running this program:

#include <stdio.h>

int main(){
unsigned int y=1;
y-=2;
printf("y=%i\n",y);

What does the %i mask in printf() expect?

I don't know, what do you mean by mask?

What mask should you specify for unsigned data?

Again, what mask? Most people associate the term "mask" with a
pattern, hopefully of an unsigned integer type, used in bitwise
operations.

The C standard uses the term "conversion specifier". It's ever so
much better than mask, don't you think?

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[Mark Bluemel]

Jack Klein wrote:

On Wed, 05 Dec 2007 10:31:46 +0000, Mark Bluemel
<ma**********@pobox.comwrote in comp.lang.c:

>Ido Yehieli wrote:

>> printf("y=%i\n",y);

What does the %i mask in printf() expect?

I don't know, what do you mean by mask?

[snip]

The C standard uses the term "conversion specifier". It's ever so
much better than mask, don't you think?

OK point taken...