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What is the proper way to handle pointers in variable arguments list?
Oct 28, 2012
Tyro[17]
Oct 28, 2012
Dmitry Olshansky
Oct 28, 2012
Tyro[17]
Oct 28, 2012
Simen Kjaeraas
Oct 28, 2012
Tyro[17]
October 28, 2012
Gravatar of Tyro[17]Posted by Tyro[17]Reply
Tyro[17]
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The following fails because the compiler assumes I am trying to dereference non-pointer variables. Can this be done?

void main()
{
    int i;
    int* pi;
    double d;
    double* pd;
    char c;
    char* pc;

    scan(i, pi, d, pd, c, pc);
}

void scan(A...)(ref A data)
{
    import std.traits;
    foreach (element; data) {
        if(isPointer!(typeof(element)) && isIntegral!(typeof(*element))) {
            *element = 10;
        }
    }
}

Thanks
October 28, 2012
Gravatar of Dmitry OlshanskyPosted by Dmitry Olshansky
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Dmitry Olshansky
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On 29-Oct-12 00:36, Tyro[17] wrote:
> The following fails because the compiler assumes I am trying to
> dereference non-pointer variables. Can this be done?
>
> void main()
> {
>      int i;
>      int* pi;
>      double d;
>      double* pd;
>      char c;
>      char* pc;
>
>      scan(i, pi, d, pd, c, pc);
> }
>
> void scan(A...)(ref A data)
> {
>      import std.traits;
>      foreach (element; data) {
>          if(isPointer!(typeof(element)) && isIntegral!(typeof(*element))) {
>              *element = 10;
>          }
>      }
> }
>
> Thanks

Well, first things first:
if ---> static if

-- 
Dmitry Olshansky
October 28, 2012
Gravatar of Tyro[17]Posted by Tyro[17]
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Tyro[17]
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Posted in reply to Dmitry Olshansky


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On 10/28/12 4:44 PM, Dmitry Olshansky wrote:
> On 29-Oct-12 00:36, Tyro[17] wrote:
>> The following fails because the compiler assumes I am trying to
>> dereference non-pointer variables. Can this be done?
>>
>> void main()
>> {
>>      int i;
>>      int* pi;
>>      double d;
>>      double* pd;
>>      char c;
>>      char* pc;
>>
>>      scan(i, pi, d, pd, c, pc);
>> }
>>
>> void scan(A...)(ref A data)
>> {
>>      import std.traits;
>>      foreach (element; data) {
>>          if(isPointer!(typeof(element)) &&
>> isIntegral!(typeof(*element))) {
>>              *element = 10;
>>          }
>>      }
>> }
>>
>> Thanks
>
> Well, first things first:
> if ---> static if
>

Changing it to static allows compilation, however I get the following runtime error:

    "Segmentation fault: 11"

This happens whether I try to read from *element or modify it.
October 28, 2012
Gravatar of Simen KjaeraasPosted by Simen Kjaeraas
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Simen Kjaeraas
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On 2012-08-28 22:10, Tyro[17] <nospam@home.com> wrote:

> On 10/28/12 4:44 PM, Dmitry Olshansky wrote:
>> On 29-Oct-12 00:36, Tyro[17] wrote:
>>> The following fails because the compiler assumes I am trying to
>>> dereference non-pointer variables. Can this be done?
>>>
>>> void main()
>>> {
>>>      int i;
>>>      int* pi;
>>>      double d;
>>>      double* pd;
>>>      char c;
>>>      char* pc;
>>>
>>>      scan(i, pi, d, pd, c, pc);
>>> }
>>>
>>> void scan(A...)(ref A data)
>>> {
>>>      import std.traits;
>>>      foreach (element; data) {
>>>          if(isPointer!(typeof(element)) &&
>>> isIntegral!(typeof(*element))) {
>>>              *element = 10;
>>>          }
>>>      }
>>> }
>>>
>>> Thanks
>>
>> Well, first things first:
>> if ---> static if
>>
>
> Changing it to static allows compilation, however I get the following runtime error:
>
>      "Segmentation fault: 11"
>
> This happens whether I try to read from *element or modify it.

I assume you've actually initialized the pointers to something?

Given the above code, all the pointers point to null, and a segfault
would be a reasonable reaction.

-- 
Simen
October 28, 2012
Gravatar of Tyro[17]Posted by Tyro[17]
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Tyro[17]
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On 10/28/12 5:16 PM, Simen Kjaeraas wrote:
> On 2012-08-28 22:10, Tyro[17] <nospam@home.com> wrote:
>
>> On 10/28/12 4:44 PM, Dmitry Olshansky wrote:
>>> On 29-Oct-12 00:36, Tyro[17] wrote:
>>>> The following fails because the compiler assumes I am trying to
>>>> dereference non-pointer variables. Can this be done?
>>>>
>>>> void main()
>>>> {
>>>>      int i;
>>>>      int* pi;
>>>>      double d;
>>>>      double* pd;
>>>>      char c;
>>>>      char* pc;
>>>>
>>>>      scan(i, pi, d, pd, c, pc);
>>>> }
>>>>
>>>> void scan(A...)(ref A data)
>>>> {
>>>>      import std.traits;
>>>>      foreach (element; data) {
>>>>          if(isPointer!(typeof(element)) &&
>>>> isIntegral!(typeof(*element))) {
>>>>              *element = 10;
>>>>          }
>>>>      }
>>>> }
>>>>
>>>> Thanks
>>>
>>> Well, first things first:
>>> if ---> static if
>>>
>>
>> Changing it to static allows compilation, however I get the following
>> runtime error:
>>
>>      "Segmentation fault: 11"
>>
>> This happens whether I try to read from *element or modify it.
>
> I assume you've actually initialized the pointers to something?
>
> Given the above code, all the pointers point to null, and a segfault
> would be a reasonable reaction.
>

Wow, so obvious yet so obviously overlooked... *banging my head on the monitor*

Thanks