If in C one codes a function which includes
return a++;
does 'a' get incremented? Would the behaviour be safe to rely upon? I
guess this might apply if 'a' were static or such as
return ptr->element++;
I didn't find this in the comp.lang.c faq (at least the first one that
came up from Google; there seemed to be many) but didn't find it. No
doubt someone will tell me where I should have looked.
(For the time being I'm coding: a++; return a - 1; )
--
James
Oct 29 '07
51  3968 
In article <47************ ***@yahoo.com>, CBFalconer
<cb********@yah oo.comwrites
>Chris Hills wrote:
>Larry__Weiss <lf*@airmail.ne twrites
... snip ...
>>
>>Do set of programs exist that attempt to validate a C
implementatio n?
Yes
>>If so, are any of these freely available?
No
Yes. The gcc test suite is freely available. However it is geared
to "gcc C" rather than ISO std C.
OFF TOPIC :-) this NG as you have REPEATEDLY told every one is for the
discussion of STANDARD C. GCC is not C it is "a C like language"
according to your oft repeated definition.
You of all people should refrain from this level of hypocrisy!
So it is NOT a C test suite.
It is a GCC build confirmation test.
Also AFAIK It falls far short of what a test suite for a compiler should
be.
See Perennial and Plum Hall for C test suites.
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ ch***@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
In article <11************ **********@v3g2 000hsg.googlegr oups.com>, Dave
Hansen <id**@hotmail.c omwrites
>On Oct 30, 11:35 am, Chris Hills <ch...@phaedsys .orgwrote:
>In article <47274b17.15255 6...@news.sbtc. net>, Richard Harter
<c...@tiac.net writes
[...]
>>
>I believe you're missing his point. Ada has a very thorough
validation suite and stringent restrictions on what may be called
an Ada compiler. This isn't the case with C compilers; anybody
can produce what they call a C compiler. It is even possible
that there is no such thing as a fully conforming C compiler.
>His point is that in the real world this is the kind of thing
that you should check whether the compiler gets it right.
Precisely
Off
hand, I would think that it is the sort of thing that a compiler
could be expected to get right but I might well be wrong.
In other words you wouldn't bet your life on it....
In that case (betting my life), Ada has no advantage over C.
"Trust, but verify."
Regards,
-=Dave
Absolutely,.... For years I have been arguing there is no such thing as
a
"safe" language. It is all down to the quality of the implementation
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ ch***@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
In article <bJ************ *********@telen or.com>, Tor Rustad
<to********@hot mail.comwrites
>Kenneth Brody wrote:
[in addition, my response applies to Kuyper and Sosman]
>Tor Rustad wrote:
[...]
>>However, in safety-critical SW, I wouldn't advocate using construct
like
return a++;
anyway.
Why not? If the compiler doesn't handle it right, then I wouldn't
trust it for the rest of the "safety-critical" program either.
First, I didn't agree with Chris Hills, because
1. I didn't find such a C compiler bug likely
"Likely" is not good enough. You have to be certain.
>2. If such a compiler bug existed, the unit test should detect it
Absolutely.
>My comment on not advocating returning a++, is more of a stylish
matter, since post conditions in functions, usually follow after the
last expression, and before the return statement.
Returning expressions, obfuscate debugging too.
I agree completely.
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ ch***@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
In article <1193844678.287 107@news1nwk>, Eric Sosman
<Er*********@su n.comwrites
>Tor Rustad wrote On 10/30/07 19:06,:
>[...]
However, in safety-critical SW, I wouldn't advocate using construct
like
return a++;
What's your opinion of `return getchar();'? Keep
in mind that in many implementations , getchar() is a
macro that expands to an expression with side-effects.
On an implementation I happen to have handy at the
moment, `return getchar();' produces (reformatted for
clarity)
return ( --(( &__iob[0]))->_cnt < 0
? __filbuf( (&__iob[0]) )
: (int) *(( &__iob[0]))->_ptr++ );
So, what's your verdict? Should `return getchar();'
be avoided in safety-critical software?
Personally I always prefer to just return a value.
I would
a = getchar();
return a;
It also helps of you are going to single step the C (as opposed to the
assembler) or you are doing white box unit testing.
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ ch***@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
Chris Hills <ch***@phaedsys .orgwrites:
In article <47************ ***@yahoo.com>, CBFalconer
<cb********@yah oo.comwrites
>>Chris Hills wrote:
>>Larry__Weis s <lf*@airmail.ne twrites
... snip ...
>>>
Do set of programs exist that attempt to validate a C
implementati on?
Yes
If so, are any of these freely available?
No
Yes. The gcc test suite is freely available. However it is geared
to "gcc C" rather than ISO std C.
OFF TOPIC :-) this NG as you have REPEATEDLY told every one is for the
discussion of STANDARD C. GCC is not C it is "a C like language"
according to your oft repeated definition.
You of all people should refrain from this level of hypocrisy!
So it is NOT a C test suite.
It is a GCC build confirmation test.
Also AFAIK It falls far short of what a test suite for a compiler
should be.
See Perennial and Plum Hall for C test suites.
I'm not familiar with the gcc test suite, but since gcc attempts to
conform to C90 and/or C95 in certain modes, I would assume that the
test suite would, among other things, test that conformance.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Chris Hills <ch***@phaedsys .orgwrites:
In article <1193844678.287 107@news1nwk>, Eric Sosman
<Er*********@su n.comwrites
>>Tor Rustad wrote On 10/30/07 19:06,:
>>[...]
However, in safety-critical SW, I wouldn't advocate using construct
like
return a++;
What's your opinion of `return getchar();'? Keep
in mind that in many implementations , getchar() is a
macro that expands to an expression with side-effects.
On an implementation I happen to have handy at the
moment, `return getchar();' produces (reformatted for
clarity)
return ( --(( &__iob[0]))->_cnt < 0
? __filbuf( (&__iob[0]) )
: (int) *(( &__iob[0]))->_ptr++ );
So, what's your verdict? Should `return getchar();'
be avoided in safety-critical software?
Personally I always prefer to just return a value.
I would
a = getchar();
return a;
Ok, that's fine -- but a compiler that mishandles ``return <expr>''
would be nearly as likely to mishandle ``a = <expr>''.
I just don't see that there's any significant need to worry more about
``return a++;'' than about any other straightforward language
construct.
If you think that something like:
result = a++;
return result;
is better style than
return a++;
I won't necessarily argue -- but either form calls for exactly the
same amount of testing.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Chris Hills <ch***@phaedsys .orgwrites:
In article <bJ************ *********@telen or.com>, Tor Rustad
<to********@hot mail.comwrites
>>Kenneth Brody wrote:
[in addition, my response applies to Kuyper and Sosman]
>>Tor Rustad wrote:
[...]
However, in safety-critical SW, I wouldn't advocate using construct
like
return a++;
anyway.
Why not? If the compiler doesn't handle it right, then I wouldn't
trust it for the rest of the "safety-critical" program either.
First, I didn't agree with Chris Hills, because
1. I didn't find such a C compiler bug likely
"Likely" is not good enough. You have to be certain.
What a pity that certainty is not possible.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Chris Hills <ch***@phaedsys .orgwrote:
In article <bJ************ *********@telen or.com>, Tor Rustad
1. I didn't find such a C compiler bug likely
"Likely" is not good enough. You have to be certain.
If you want certainty, you'll have to unplug your computer.
No, just turning it off may not be enough to be certain.
Richard
Keith Thompson said:
Chris Hills writes:
>Tor Rustad writes
<snip>
>>>1. I didn't find such a C compiler bug likely
"Likely" is not good enough. You have to be certain.
What a pity that certainty is not possible.
Are you sure about that?
--
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
Richard Heathfield wrote:
Keith Thompson said:
....
>What a pity that certainty is not possible.
Are you sure about that?
Reasonably sure, but not certain. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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