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bert wrote:
> On 30 Mar, 19:11, Richard <de...@xxxxxxxxx> wrote:
>> bert <bert.hutchi...@xxxxxxxxxxxxxx> writes:
>>> On 30 Mar, 15:02, Philip Potter <p...@xxxxxxxxxxxx> wrote:
>>>> Rahul wrote:
>>>>> int main()
>>>>> {
>>>>> int aa=0,b=0;
>>>>> 1>0?aa:b = 10;
>>>>> printf("value %d %d\n",aa,b);
>>>>> return(0);
>>>>> }
>>
>>>>> and output is value 0 0
>>>> The result of the ?: operator is not an lvalue, and cannot be
>>>> assigned to.
>>
>>>> If you want to conditionally assign to one of two objects, it's
>>>> probably clearer to write it in full:
>>
>>>> if (1>0)
>>>> aa = 0;
>>>> else
>>>> b = 10;
>>
>>>> If you really want unreadable code, I suppose you could do this:
>>>> int *ip[2] = {&b,&aa};
>>
>>>> *ip[1>0] = 10;
>>
>>>> but if I worked with you I wouldn't thank you for it :)
>>
>>> For such requirements, I have written - and
>>> been satisfied with - code of the style:
>>
>>> *(i > 0 ? &aa : &b) = <complicated expression>;
>>
>> Well done - you'll make maintainers very happy in years to come.
>
> I can't decide whether that's sarcasm from you, or real praise.
I don't think it was praise..
>
>> What on earth is wrong with
>>
>> v= complex expr;
>> if(i)
>> aa=v;
>> else
>> b=v;
>>
>> Same number of characters give or take too .... Easy to see
>> flow/assignment in a debugger too. Very easy to read.- Hide quoted
>> text -
>
> The main thing "wrong" with your alternative
> is the omission of a block structure.
>
> {
> int v = complicated expression;
> if (i)
> aa = v;
> else
> b = v;
> }
>
> would make it perfectly clear to a maintainer
> in years to come that the only purpose of v
> was to be assigned either to aa or to b.
There was nothing much wrong with the original syntax:
a ? b : c = x;
(maybe better as (a ? b : c) = x;)
except that C doesn't allow it, and it's unfortunate that the legal format
is a little messy:
*(a ? &b ? &c) = x;
This is what the programmer wants to do, so why force him to create
unnecessary statements and to duplicate expressions, or declare unnecessary
temporary variables? All extra clutter.
Exactly why a?b:c can't appear like that on the left-hand-side of an
assignment is a bit of a mystery; after all a, a.b, a->b, a[b] and so on can
all appear on the lhs without the programmer having to insert explicit
address-of operators.
--
Bart
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