scope tmp 	= new ubyte[4];


Error: TypeInfo cannot be used with -betterC


how to bypass this ?

On 23/10/2018 6:20 PM, test wrote:
> 
> scope tmp     = new ubyte[4];
> 
> 
> Error: TypeInfo cannot be used with -betterC
> 
> 
> how to bypass this ?

new only exists thanks to druntime hooks.
So no by-pass. You just can't use it.

On Tuesday, 23 October 2018 at 05:23:42 UTC, rikki cattermole wrote:
> On 23/10/2018 6:20 PM, test wrote:
>> 
>> scope tmp     = new ubyte[4];
>> 
>> 
>> Error: TypeInfo cannot be used with -betterC
>> 
>> 
>> how to bypass this ?
>
> new only exists thanks to druntime hooks.
> So no by-pass. You just can't use it.

so how to do in pure C code ?  can we use that method in D ?

On 23/10/2018 6:26 PM, test wrote:
> On Tuesday, 23 October 2018 at 05:23:42 UTC, rikki cattermole wrote:
>> On 23/10/2018 6:20 PM, test wrote:
>>>
>>> scope tmp     = new ubyte[4];
>>>
>>>
>>> Error: TypeInfo cannot be used with -betterC
>>>
>>>
>>> how to bypass this ?
>>
>> new only exists thanks to druntime hooks.
>> So no by-pass. You just can't use it.
> 
> so how to do in pure C code ?  can we use that method in D ?

Yup, call malloc or do the allocation on the stack just like in C.

On Tuesday, 23 October 2018 at 05:32:14 UTC, rikki cattermole wrote:
> On 23/10/2018 6:26 PM, test wrote:
>> On Tuesday, 23 October 2018 at 05:23:42 UTC, rikki cattermole wrote:
>>> On 23/10/2018 6:20 PM, test wrote:
>>>>
>>>> scope tmp     = new ubyte[4];
>>>>
>>>>
>>>> Error: TypeInfo cannot be used with -betterC
>>>>
>>>>
>>>> how to bypass this ?
>>>
>>> new only exists thanks to druntime hooks.
>>> So no by-pass. You just can't use it.
>> 
>> so how to do in pure C code ?  can we use that method in D ?
>
> Yup, call malloc or do the allocation on the stack just like in C.

correct if I am wrong,  I think malloc is on heap and is very slow.

On Tuesday, 23 October 2018 at 05:36:00 UTC, test wrote:
> correct if I am wrong,  I think malloc is on heap and is very slow.

Yes, you probably want a static array on the stack:

```
scope ubyte[4] tmp = void; // or a default value
```

This is analogous to this C (except scope):
```
unsigned char tmp[4];
```

While 'new' is analogous to 'malloc'.

On Tuesday, 23 October 2018 at 07:59:53 UTC, Dennis wrote:
> On Tuesday, 23 October 2018 at 05:36:00 UTC, test wrote:
>> correct if I am wrong,  I think malloc is on heap and is very slow.
>
> Yes, you probably want a static array on the stack:
>
> ```
> scope ubyte[4] tmp = void; // or a default value
> ```
>
> This is analogous to this C (except scope):
> ```
> unsigned char tmp[4];
> ```
>
> While 'new' is analogous to 'malloc'.

I can not user static array because the length is a runtime vars.

On Tuesday, 23 October 2018 at 10:18:56 UTC, test wrote:
> I can not user static array because the length is a runtime vars.

Then you can either:
- use malloc anyway (recommended when the array can be quite large)
- allocate a static array with an upper bound, and only use a slice of it
- use alloca to allocate on the stack. Watch out for stack overflows though.
```
import core.stdc.stdlib: alloca;
import core.stdc.stdio: printf;
extern(C) void main()
{
    int n = 5;
    ubyte[] tmp = (cast(ubyte*) alloca(ubyte.sizeof * n))[0..n];
    tmp[4] = 22;
    printf("%d", tmp[4]);
}
```
When compiling with dmd and -betterC I got a linker error "undefined reference to '__alloca'", but with LDC it worked fine.

On Tuesday, 23 October 2018 at 05:36:00 UTC, test wrote:
> On Tuesday, 23 October 2018 at 05:32:14 UTC, rikki cattermole wrote:
>>
>> Yup, call malloc or do the allocation on the stack just like in C.
>
> correct if I am wrong,  I think malloc is on heap and is very slow.

new is also on the heap. I would guess the speed of new and malloc is very similar.

On Tuesday, 23 October 2018 at 11:17:03 UTC, Dennis wrote:
> On Tuesday, 23 October 2018 at 10:18:56 UTC, test wrote:
>> I can not user static array because the length is a runtime vars.
> When compiling with dmd and -betterC I got a linker error "undefined reference to '__alloca'", but with LDC it worked fine.



Thanks,  alloca is what i am look for.


to @Tony

when you use "scope tmp = new ubyte[4]", it is much fast then malloc because it is on stack.