Hi,

I need to call a C function within a DLL which has following signature:
  void GetParamNames (const char *paramNames[], size_t numParams);

The purpose of this function is to return a list of texts
I defined in D:
extern(C) GetParamNames (const char[]* paramNames, size_t numParams);

Is this correct? How can I call the function? I tried several possibilities but
always get a runtime crash.

Kind regards
André

On Monday, 9 July 2018 at 10:33:03 UTC, Andre Pany wrote:
> Hi,
>
> I need to call a C function within a DLL which has following signature:
>   void GetParamNames (const char *paramNames[], size_t numParams);
>
> The purpose of this function is to return a list of texts
> I defined in D:
> extern(C) GetParamNames (const char[]* paramNames, size_t numParams);
>
> Is this correct? How can I call the function? I tried several possibilities but
> always get a runtime crash.
>
> Kind regards
> André

Hi, no it's not correct i think, right translation would be

    extern(C) void GetParamNames(const char** paramNames, size_t numParams);

If you use the D array syntax you'll get into troubles because of ABI i think.

Baz.

On Monday, 9 July 2018 at 10:38:54 UTC, Basile B. wrote:
> On Monday, 9 July 2018 at 10:33:03 UTC, Andre Pany wrote:
> Hi, no it's not correct i think, right translation would be
>
>     extern(C) void GetParamNames(const char** paramNames, size_t numParams);
>
> If you use the D array syntax you'll get into troubles because of ABI i think.
>
> Baz.

Thanks, it seems I also have to allocate the pointer before with the numbers of numParams.
In python the code looks s.th. like this

self.output_names = (c_char_p * self.number_outputs)()

Do you know that is the equivalent in D?

Kind regards
André

On Monday, 9 July 2018 at 10:56:18 UTC, Andre Pany wrote:
> On Monday, 9 July 2018 at 10:38:54 UTC, Basile B. wrote:
>> On Monday, 9 July 2018 at 10:33:03 UTC, Andre Pany wrote:
>> Hi, no it's not correct i think, right translation would be
>>
>>     extern(C) void GetParamNames(const char** paramNames, size_t numParams);
>>
>> If you use the D array syntax you'll get into troubles because of ABI i think.
>>
>> Baz.
>
> Thanks, it seems I also have to allocate the pointer before with the numbers of numParams.
> In python the code looks s.th. like this
>
> self.output_names = (c_char_p * self.number_outputs)()
>
> Do you know that is the equivalent in D?
>
> Kind regards
> André

If found this working, is this OK, or do I have a memory bug here?

        import core.stdc.stdlib: malloc, free;
        string[] result;

        size_t numOutputs = 4;
        const(char**) arr = cast (const(char**)) malloc(numOutputs * (char*).sizeof);

        auto status = GetParamNames(arr, numOutputs);

        for(int i = 0; i < numOutputs; i++)
        {
            const(char*) c = arr[i];
            result ~= c.fromStringz.dup;
        }

        free(cast(void*) arr);

Kind regards
André

On Monday, 9 July 2018 at 10:56:18 UTC, Andre Pany wrote:
> On Monday, 9 July 2018 at 10:38:54 UTC, Basile B. wrote:
>> On Monday, 9 July 2018 at 10:33:03 UTC, Andre Pany wrote:
>> Hi, no it's not correct i think, right translation would be
>>
>>     extern(C) void GetParamNames(const char** paramNames, size_t numParams);
>>
>> If you use the D array syntax you'll get into troubles because of ABI i think.
>>
>> Baz.
>
> Thanks, it seems I also have to allocate the pointer before with the numbers of numParams.
> In python the code looks s.th. like this
>
> self.output_names = (c_char_p * self.number_outputs)()
>
> Do you know that is the equivalent in D?
>
> Kind regards
> André

you don't need to allocate but to retrieve each string, do something like this:

    foreach(i; 0 .. numParams)
    {
        string p = fromStringz(paramNames + i)
    }

although i have a doubt for pointer arithmetic. Maybe it should be incremented by

    i * size_t.sizeof

since char.sizeof is 1. Maybe someone else will be more helpful here.

Baz.

On Monday, 9 July 2018 at 11:10:01 UTC, Basile B. wrote:
> On Monday, 9 July 2018 at 10:56:18 UTC, Andre Pany wrote:
>> On Monday, 9 July 2018 at 10:38:54 UTC, Basile B. wrote:
>>> On Monday, 9 July 2018 at 10:33:03 UTC, Andre Pany wrote:
>>> Hi, no it's not correct i think, right translation would be
>>>
>>>     extern(C) void GetParamNames(const char** paramNames, size_t numParams);
>>>
>>> If you use the D array syntax you'll get into troubles because of ABI i think.
>>>
>>> Baz.
>>
>> Thanks, it seems I also have to allocate the pointer before with the numbers of numParams.
>> In python the code looks s.th. like this
>>
>> self.output_names = (c_char_p * self.number_outputs)()
>>
>> Do you know that is the equivalent in D?
>>
>> Kind regards
>> André
>
> you don't need to allocate but to retrieve each string, do something like this:
>
>     foreach(i; 0 .. numParams)
>     {
>         string p = fromStringz(paramNames + i)
>     }
>
> although i have a doubt for pointer arithmetic. Maybe it should be incremented by
>
>     i * size_t.sizeof
>
> since char.sizeof is 1. Maybe someone else will be more helpful here.
>
> Baz.

Ok, i've read your other answers and it seems that you have a way to test so i think you'll figure it out yourself, but you don't need to alloc. Once the fromStringz verified to be good maybe dup/idup in case the C lib free the stuff but that's all.

On Monday, 9 July 2018 at 11:39:46 UTC, Basile B. wrote:
>
> Ok, i've read your other answers and it seems that you have a way to test so i think you'll figure it out yourself, but you don't need to alloc. Once the fromStringz verified to be good maybe dup/idup in case the C lib free the stuff but that's all.

Thanks a lot for your help.

Kind regards
André

        const(char)*[] znames;
        znames.length=4;
        GetParamNames(znames.ptr, znames.length);
        const char[][] names=znames.map!fromStringz.array;

Correct signature:
extern(C) void GetParamNames(const(char)** paramNames, size_t numParams);
In C const applies only to the nearest member.

On Monday, 9 July 2018 at 13:48:05 UTC, Kagamin wrote:
> Correct signature:
> extern(C) void GetParamNames(const(char)** paramNames, size_t numParams);
> In C const applies only to the nearest member.

Thank you, that looks great.

Kind regards
Andre