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February 24, 2012
Cannot cast void* to arrays..?
char[] a;
    auto b = cast(void*)a;
    auto c = cast(char[])b; // Error: e2ir: cannot cast b of type void* to  
type char[]
February 24, 2012
Re: Cannot cast void* to arrays..?
On Fri, 24 Feb 2012 20:34:19 +0100, simendsjo wrote:

> char[] a;
>      auto b = cast(void*)a;
>      auto c = cast(char[])b; // Error: e2ir: cannot cast b of type void*
>      to
> type char[]

Arrays have a length--you need to cast the pointer to a char*, then slice 
it.
February 24, 2012
Re: Cannot cast void* to arrays..?
On Fri, 24 Feb 2012 20:42:20 +0100, Justin Whear  
<justin@economicmodeling.com> wrote:

> On Fri, 24 Feb 2012 20:34:19 +0100, simendsjo wrote:
>
>> char[] a;
>>      auto b = cast(void*)a;
>>      auto c = cast(char[])b; // Error: e2ir: cannot cast b of type void*
>>      to
>> type char[]
>
> Arrays have a length--you need to cast the pointer to a char*, then slice
> it.

Ah, of course, thanks.
But what about static arrays?
    char[1] a;
    //a.length = 10; // constant a.length is not an lvalue
    auto b = cast(void*)a;
    auto c = cast(char[1])b; // Error: e2ir: cannot cast b of type void*  
to type char[1LU]
February 24, 2012
Re: Cannot cast void* to arrays..?
On Fri, Feb 24, 2012 at 08:34:19PM +0100, simendsjo wrote:
>     char[] a;
>     auto b = cast(void*)a;
>     auto c = cast(char[])b; // Error: e2ir: cannot cast b of type
> void* to type char[]

D arrays are not the same as C arrays. D arrays also include length in
addition to the pointer, so you can't just cast a void* to an array.


T

-- 
Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it. -- Brian W. Kernighan
February 24, 2012
Re: Cannot cast void* to arrays..?
24.02.2012 21:34, simendsjo пишет:
>     char[] a;
>     auto b = cast(void*)a;
>     auto c = cast(char[])b; // Error: e2ir: cannot cast b of type 
> void* to type char[]
>
Generally, you should not cast a struct to pointer and vise-versa. 
Besides, size of array structure is larger than size of pointer, and 
that triggers error in your case.
February 24, 2012
Re: Cannot cast void* to arrays..?
> 24.02.2012 21:34, simendsjo пишет:
> >    char[] a;
> >    auto b = cast(void*)a;
> >    auto c = cast(char[])b; // Error: e2ir: cannot cast b of type
> >void* to type char[]
[...]

Just out of curiosity, what are you trying to accomplish with this cast?
In almost all normal D code, there's no need for any casting at all.


T

-- 
The right half of the brain controls the left half of the body. This
means that only left-handed people are in their right mind. -- Manoj
Srivastava
February 24, 2012
Re: Cannot cast void* to arrays..?
On 02/24/2012 11:44 AM, simendsjo wrote:
> On Fri, 24 Feb 2012 20:42:20 +0100, Justin Whear
> <justin@economicmodeling.com> wrote:
>
>> On Fri, 24 Feb 2012 20:34:19 +0100, simendsjo wrote:
>>
>>> char[] a;
>>> auto b = cast(void*)a;
>>> auto c = cast(char[])b; // Error: e2ir: cannot cast b of type void*
>>> to
>>> type char[]
>>
>> Arrays have a length--you need to cast the pointer to a char*, then slice
>> it.
>
> Ah, of course, thanks.
> But what about static arrays?
> char[1] a;
> //a.length = 10; // constant a.length is not an lvalue
> auto b = cast(void*)a;
> auto c = cast(char[1])b; // Error: e2ir: cannot cast b of type void* to
> type char[1LU]

    char[1] a;
    auto c = a.ptr[0..a.length];

Ali
February 24, 2012
Re: Cannot cast void* to arrays..?
On Fri, 24 Feb 2012 20:56:18 +0100, Ali Çehreli <acehreli@yahoo.com> wrote:

> On 02/24/2012 11:44 AM, simendsjo wrote:
>> On Fri, 24 Feb 2012 20:42:20 +0100, Justin Whear
>> <justin@economicmodeling.com> wrote:
>>
>>> On Fri, 24 Feb 2012 20:34:19 +0100, simendsjo wrote:
>>>
>>>> char[] a;
>>>> auto b = cast(void*)a;
>>>> auto c = cast(char[])b; // Error: e2ir: cannot cast b of type void*
>>>> to
>>>> type char[]
>>>
>>> Arrays have a length--you need to cast the pointer to a char*, then  
>>> slice
>>> it.
>>
>> Ah, of course, thanks.
>> But what about static arrays?
>> char[1] a;
>> //a.length = 10; // constant a.length is not an lvalue
>> auto b = cast(void*)a;
>> auto c = cast(char[1])b; // Error: e2ir: cannot cast b of type void* to
>> type char[1LU]
>
>      char[1] a;
>      auto c = a.ptr[0..a.length];
>
> Ali


I don't get it. This gives me a dynamic array, not a static:
    char[1] a;
    auto b = cast(void*)a;
    auto c = (cast(char*)b)[0..1];
    c.length = 10; // auch!
February 24, 2012
Re: Cannot cast void* to arrays..?
On Fri, 24 Feb 2012 20:56:22 +0100, H. S. Teoh <hsteoh@quickfur.ath.cx>  
wrote:

>> 24.02.2012 21:34, simendsjo пишет:
>> >    char[] a;
>> >    auto b = cast(void*)a;
>> >    auto c = cast(char[])b; // Error: e2ir: cannot cast b of type
>> >void* to type char[]
> [...]
>
> Just out of curiosity, what are you trying to accomplish with this cast?
> In almost all normal D code, there's no need for any casting at all.
>
>
> T
>

Interacting with a C callback taking a void*. In my callback, I want to  
get the same type back.
See my previous question:  
http://forum.dlang.org/post/op.v963zyg0x8p62v@simendsjo-desktop (although  
I didn't include the parameters in that example)
February 24, 2012
Re: Cannot cast void* to arrays..?
On Fri, Feb 24, 2012 at 11:56:18AM -0800, Ali Çehreli wrote:
[...]
>     char[1] a;
>     auto c = a.ptr[0..a.length];
[...]

Hey, that's an awesome way to implement copy-on-write static arrays!

I'll have to use that sometime. :)


T

-- 
Sometimes the best solution to morale problems is just to fire all of
the unhappy people. -- despair.com
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