gcc: What's illegal about this ?

**Harald van =?UTF-8?b?RMSzaw==?=** · Mar 14 '08, 06:05 PM

Re: gcc: What's illegal about this ?

On Fri, 14 Mar 2008 17:49:16 +0000, Richard Eich wrote:

I need a clue. I'm getting an "invalid lvalue in increment" from gcc
4.1.2 on this line...
>
sum += *((unsigned short *)iphp)++ ;
>
...but I don't see what the problem is. gcc 3.4.3 isn't bother by it,
either.

(unsigned short *)iphp is not an lvalue. Where do you want to store
(unsigned short *)iphp + 1? Presumably, you want to store it in iphp. If
you want that, write that.

sum += *((unsigned short *)iphp);
iphp = ((unsigned short *)iphp) + 1;

You can consider it similar to
int i;
(i + 1) = -1;
(double) i = 1.5;

**Ben Pfaff** · Mar 14 '08, 06:05 PM

Re: gcc: What's illegal about this ?

Richard Eich <richard.eich@d omain.invalidwr ites:

I need a clue. I'm getting an "invalid lvalue in increment" from gcc
4.1.2 on this line...
>
sum += *((unsigned short *)iphp)++ ;

The part that GCC is complaining about is this:
((unsigned short *)iphp)++
which attempts to increment the result of a cast. The result of
a cast is never an lvalue, so you can't increment it. (GCC used
to have an extension that permits this, but it was removed.)

Perhaps you really mean:
sum += (*((unsigned short *)iphp))++ ;
--
char a[]="\n .CJacehknorstu" ;int putchar(int);in t main(void){unsi gned long b[]
={0x67dffdff,0x 9aa9aa6a,0xa77f fda9,0x7da6aa6a ,0xa67f6aaa,0xa a9aa9f6,0x11f6} ,*p
=b,i=24;for(;p+ =!*p;*p/=4)switch(0[p]&3)case 0:{return 0;for(p--;i--;i--)case+
2:{i++;if(i)bre ak;else default:continu e;if(0)case 1:putchar(a[i&15]);break;}}}

**ymuntyan@gmail.com** · Mar 14 '08, 06:15 PM

Re: gcc: What's illegal about this ?

On Mar 14, 12:49 pm, Richard Eich <richard.e...@d omain.invalidwr ote:

I need a clue. I'm getting an "invalid lvalue in increment" from gcc
4.1.2 on this line...
>
sum += *((unsigned short *)iphp)++ ;
>
...but I don't see what the problem is. gcc 3.4.3 isn't bother by
it, either.

Your code is invalid, result of a cast is not an lvalue
(and hence not something you can apply ++ to). Quoting

GCC 3.4 Release Series — Changes, New Features, and Fixes - GNU Project

http://gcc.gnu.org/gcc-3.4/changes.html

"""
The cast-as-lvalue extension has been removed for C++ and
deprecated for C and Objective-C. In particular, code like this:
int i;
(char) i = 5;
or this:
char *p;
((int *) p)++;
is no longer accepted for C++ and will not be accepted for C
and Objective-C in a future version.
"""

And "future version" was 4.something.

Yevgen

**Aaron Hsu** · Mar 14 '08, 06:55 PM

Re: gcc: What's illegal about this ?

Richard Eich <richard.eich@d omain.invalidwr ites:

>I need a clue. I'm getting an "invalid lvalue in increment" from gcc
>4.1.2 on this line...

> sum += *((unsigned short *)iphp)++ ;

>...but I don't see what the problem is. gcc 3.4.3 isn't bother by
>it, either.

I think it would help if you could give us just a bit of context, at least.
--
Aaron Hsu <arcfide@sacrid eo.us| Jabber: arcfide@jabber. org
``Government is the great fiction through which everybody endeavors to
live at the expense of everybody else.'' - Frederic Bastiat

**Richard Tobin** · Mar 14 '08, 11:35 PM

Re: gcc: What's illegal about this ?

In article <MPG.224484a711 0ac91798b037@ne ws.verizon.net> ,
Richard Eich <richard.eich@d omain.invalidwr ote:

>I need a clue. I'm getting an "invalid lvalue in increment" from gcc
>4.1.2 on this line...
>
> sum += *((unsigned short *)iphp)++ ;
>
>...but I don't see what the problem is. gcc 3.4.3 isn't bother by
>it, either.

It's an extension in earlier versions of gcc, was accepted by
some other C compilers before the ANSI standard, and was allowed in
early drafts of the ANSI standard, but it not allowed now.

-- Richard
--
:wq

**CBFalconer** · Mar 15 '08, 12:05 AM

Re: gcc: What's illegal about this ?

Aaron Hsu wrote:

Richard Eich <richard.eich@d omain.invalidwr ites:
>

>I need a clue. I'm getting an "invalid lvalue in increment"
>from gcc 4.1.2 on this line...

>

> sum += *((unsigned short *)iphp)++ ;

>

>...but I don't see what the problem is. gcc 3.4.3 isn't bother
>by it, either.

>
I think it would help if you could give us just a bit of context,
at least.

In this case at least, why? That line of code is obviously wrong.
Evem before the very queasy integer to pointer cast.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

--
Posted via a free Usenet account from http://www.teranews.com

**ymuntyan@gmail.com** · Mar 15 '08, 01:25 AM

Re: gcc: What's illegal about this ?

On Mar 14, 4:48 pm, CBFalconer <cbfalco...@yah oo.comwrote:

Aaron Hsu wrote:

Richard Eich <richard.e...@d omain.invalidwr ites:

>

I need a clue. I'm getting an "invalid lvalue in increment"
from gcc 4.1.2 on this line...

>

sum += *((unsigned short *)iphp)++ ;

>

...but I don't see what the problem is. gcc 3.4.3 isn't bother
by it, either.

>

I think it would help if you could give us just a bit of context,
at least.

>
In this case at least, why? That line of code is obviously wrong.
Evem before the very queasy integer to pointer cast.

So context indeed would be helpful, because there is no
integer to pointer cast ;)

Yevgen

**Kenny McCormack** · Mar 15 '08, 03:25 PM

Re: gcc: What's illegal about this ?

In article <frf1qq$1of2$1@ pc-news.cogsci.ed. ac.uk>,
Richard Tobin <richard@cogsci .ed.ac.ukwrote:

>In article <MPG.224484a711 0ac91798b037@ne ws.verizon.net> ,
>Richard Eich <richard.eich@d omain.invalidwr ote:

>>I need a clue. I'm getting an "invalid lvalue in increment" from gcc
>>4.1.2 on this line...
>>
>> sum += *((unsigned short *)iphp)++ ;
>>
>>...but I don't see what the problem is. gcc 3.4.3 isn't bother by
>>it, either.

>
>It's an extension in earlier versions of gcc, was accepted by
>some other C compilers before the ANSI standard, and was allowed in
>early drafts of the ANSI standard, but it not allowed now.
>
>-- Richard
>--
>:wq

What did it do?

As has been pointed out, it doesn't make any sense, so I'm having a hard
time imagining what it did in prior versions of gcc?

**Harald van =?UTF-8?b?RMSzaw==?=** · Mar 15 '08, 03:35 PM

Re: gcc: What's illegal about this ?

On Sat, 15 Mar 2008 15:23:06 +0000, Kenny McCormack wrote:

In article <frf1qq$1of2$1@ pc-news.cogsci.ed. ac.uk>, Richard Tobin
<richard@cogsci .ed.ac.ukwrote:

>>In article <MPG.224484a711 0ac91798b037@ne ws.verizon.net> , Richard Eich
>><richard.eich @domain.invalid wrote:

>>>I need a clue. I'm getting an "invalid lvalue in increment" from gcc
>>>4.1.2 on this line...
>>>
>>> sum += *((unsigned short *)iphp)++ ;
>>>
>>>...but I don't see what the problem is. gcc 3.4.3 isn't bother by it,
>>>either.

>>
>>It's an extension in earlier versions of gcc, was accepted by some other
>>C compilers before the ANSI standard, and was allowed in early drafts of
>>the ANSI standard, but it not allowed now.

>
What did it do?
>
As has been pointed out, it doesn't make any sense, so I'm having a hard
time imagining what it did in prior versions of gcc?

In those versions, (ptrtype) ptrlvalue was treated in some (but not all)
contexts as *(ptrtype *) &ptrlvalue, except without aliasing problems (if
those versions understood aliasing at all).

**Richard Tobin** · Mar 15 '08, 04:55 PM

Re: gcc: What's illegal about this ?

In article <e518f$47dbebd1 $541dfcd3$16772 @cache6.tilbu1. nb.home.nl>,
Harald van DÄ³k <truedfx@gmail. comwrote:

>As has been pointed out, it doesn't make any sense, so I'm having a hard
>time imagining what it did in prior versions of gcc?

>In those versions, (ptrtype) ptrlvalue was treated in some (but not all)
>contexts as *(ptrtype *) &ptrlvalue, except without aliasing problems (if
>those versions understood aliasing at all).

Though it's similar in effect to that expression, I would have hoped
it didn't rely on the pointer types having to the same representation,
which that does.

I would expect *(ptrtype *)ptrlvalue++ to be interpreted as
*(ptrtype *)ptrlvalue for the purpose of retrieving the value,
and as ptrlvalue = (type_of_ptrlva lue)(((ptrtype *)ptrlvalue) + 1)
for the side effect.

-- Richard
--
:wq

**Harald van =?UTF-8?b?RMSzaw==?=** · Mar 15 '08, 05:05 PM

Re: gcc: What's illegal about this ?

On Sat, 15 Mar 2008 16:53:35 +0000, Richard Tobin wrote:

In article <e518f$47dbebd1 $541dfcd3$16772 @cache6.tilbu1. nb.home.nl>,
Harald van DÄ³k <truedfx@gmail. comwrote:

>>As has been pointed out, it doesn't make any sense, so I'm having a
>>hard time imagining what it did in prior versions of gcc?

>

>>In those versions, (ptrtype) ptrlvalue was treated in some (but not all)
>>contexts as *(ptrtype *) &ptrlvalue, except without aliasing problems
>>(if those versions understood aliasing at all).

>
Though it's similar in effect to that expression, I would have hoped it
didn't rely on the pointer types having to the same representation,
which that does.

Correct. I don't believe gcc has been ported to systems where different
pointer types have different representations (though I would be pleased
if proved wrong on this).

**CBFalconer** · Mar 16 '08, 02:05 AM

Re: gcc: What's illegal about this ?

ymuntyan@gmail. com wrote:

CBFalconer <cbfalco...@yah oo.comwrote:

>Aaron Hsu wrote:

>>Richard Eich <richard.e...@d omain.invalidwr ites:

>>

>>>I need a clue. I'm getting an "invalid lvalue in increment"
>>>from gcc 4.1.2 on this line...
>>>>
>>> sum += *((unsigned short *)iphp)++ ;
>>>>
>>>...but I don't see what the problem is. gcc 3.4.3 isn't bother
>>>by it, either.
>>>
>>I think it would help if you could give us just a bit of context,
>>at least.

>>
>In this case at least, why? That line of code is obviously wrong.
>Evem before the very queasy integer to pointer cast.

>
So context indeed would be helpful, because there is no
integer to pointer cast ;)

iphp is cast to a pointer. Besides which the ++ operates on the
cast value, which is illegal. If iphp isn't integral things are
even worse.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

--
Posted via a free Usenet account from http://www.teranews.com

**ymuntyan@gmail.com** · Mar 16 '08, 02:45 AM

Re: gcc: What's illegal about this ?

On Mar 15, 6:30 pm, CBFalconer <cbfalco...@yah oo.comwrote:

ymunt...@gmail. com wrote:

CBFalconer <cbfalco...@yah oo.comwrote:

Aaron Hsu wrote:
>Richard Eich <richard.e...@d omain.invalidwr ites:

>

>>I need a clue. I'm getting an "invalid lvalue in increment"
>>from gcc 4.1.2 on this line...

>

>> sum += *((unsigned short *)iphp)++ ;

>

>>...but I don't see what the problem is. gcc 3.4.3 isn't bother
>>by it, either.

>

>I think it would help if you could give us just a bit of context,
>at least.

>

In this case at least, why? That line of code is obviously wrong.
Evem before the very queasy integer to pointer cast.

>

So context indeed would be helpful, because there is no
integer to pointer cast ;)

>
iphp is cast to a pointer.

It is, but it's a pointer from the very beginning.

char *iphp; // guessed
sum += *((unsigned short *)iphp)++ ;

Besides which the ++ operates on the
cast value, which is illegal.

Yep.

If iphp isn't integral things are
even worse.

Not really.

Yevgen

**CBFalconer** · Mar 17 '08, 01:25 AM

Re: gcc: What's illegal about this ?

ymuntyan@gmail. com wrote:

CBFalconer <cbfalco...@yah oo.comwrote:

>ymunt...@gmail .com wrote:

>>CBFalconer <cbfalco...@yah oo.comwrote:
>>>Aaron Hsu wrote:
>>>>Richard Eich <richard.e...@d omain.invalidwr ites:
>>>>>
>>>>>I need a clue. I'm getting an "invalid lvalue in increment"
>>>>>from gcc 4.1.2 on this line...
>>>>>>
>>>>> sum += *((unsigned short *)iphp)++ ;
>>>>>>
>>>>>...but I don't see what the problem is. gcc 3.4.3 isn't
>>>>>bother by it, either.
>>>>>
>>>>I think it would help if you could give us just a bit of
>>>>context, at least.
>>>>
>>>In this case at least, why? That line of code is obviously
>>>wrong. Evem before the very queasy integer to pointer cast.
>>>
>>So context indeed would be helpful, because there is no
>>integer to pointer cast ;)

>>
>iphp is cast to a pointer.

>
It is, but it's a pointer from the very beginning.

So what? The only conversion available is to a void*, and from a
void* back to the original form. All others are illegal.

>
char *iphp; // guessed
sum += *((unsigned short *)iphp)++ ;
>

>Besides which the ++ operates on the cast value, which is illegal.

>
Yep.
>

>If iphp isn't integral things are even worse.

>
Not really.

Yes, really. Read the C standard.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

--
Posted via a free Usenet account from http://www.teranews.com

gcc: What's illegal about this ?

gcc: What's illegal about this ?

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