no warning for data truncation?

[david]

I've noticed that the following compiles (as C) under both VS8 and gcc
with no warnings, even though there's a possibility of data truncation
from enum to unsigned char. It does generate a warning under VS6,
however. Under VS8, I enabled run-time checks, including /RTCc
(smaller type check), but still no warning. The only way I can get a
warning under VS8 is if I configure it to compile as C++.

Two questions:
(1) why doesn't /RTCc pick up the data truncation (enum to unsigned
char)?
(2) is there any way to configure VS8 (aside from compiling as C++)
that will generate a warning?

Here's the code:

#include <string.h>
#include <stdio.h>
#include <stdlib.h>

void foo(unsigned char result);
void bar(void);

typedef enum {

OK = 0,
NOT_OK = 1,
NO_STATUS = 0xffff

} STATUS;

int main(int argc, char* argv[])
{
bar();
printf("%d %s", argc, argv[0]);
return 0;
}

void bar(void)
{
STATUS status = OK;
foo(status);
}

void foo(unsigned char result)
{
result++;
return;
}

[Richard Heathfield]

Re: no warning for data truncation?

david said:

I've noticed that the following compiles (as C) under both VS8 and gcc
with no warnings, even though there's a possibility of data truncation
from enum to unsigned char.

That's not a syntax error or a constraint violation, so implementations are
not required to diagnose it. They may *choose* to diagnose it.

I get a warning from gcc:

foo.c:26: warning: passing arg 1 of `foo' with different width due to
prototype

(2) is there any way to configure VS8 (aside from compiling as C++)
that will generate a warning?

Firstly, make sure /W4 and /Za are switched on. Failing that, I suggest you
take this up in a Windows group, comp.os.ms-windows.program mer.win32 being
the obvious choice to start off with, since that group is more likely to
have a good solid core of VS8 experts than is comp.lang.c. But you may
find that they, in turn, refer you to a Microsoft-hosted group.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[david]

Re: no warning for data truncation?

On Oct 23, 4:40 pm, Richard Heathfield <r...@see.sig.i nvalidwrote:

>
Firstly, make sure /W4 and /Za are switched on. Failing that, I suggest you

Thanks for the tip. Using /W4 and /Za caused the following warning:

warning C4244: 'function' : conversion from 'STATUS' to 'unsigned
char', possible loss of data

Which is what I was hoping to see.

Cheers.