Hi there,

I'm coming from PHP and am very new to compiled languages, so maybe I'm completely wrong.

I have the following bitsort.d:

import std.stdio;
struct List {
        uint value;
}
void main() {
        List* list;
        writefln("This is shown.");
        list.value = 5;
        writefln("This is not shown.");
}

And this happens:

peter@tux ~/D $ dmd bitsort.d
gcc bitsort.o -o bitsort -m32 -lphobos -lpthread -lm
peter@tux ~/D $ ./bitsort
This is shown.
Segmentation fault (core dumped)
peter@tux ~/D $


Is this a bug?
Peter

Peter Thomassen wrote:
> Hi there,
> 
> I'm coming from PHP and am very new to compiled languages, so maybe I'm
> completely wrong.
> 
> I have the following bitsort.d:
> 
> import std.stdio;
> struct List {
>         uint value;
> }
> void main() {
>         List* list;
>         writefln("This is shown.");
>         list.value = 5;
>         writefln("This is not shown.");
> }
> 
> And this happens:
> 
> peter@tux ~/D $ dmd bitsort.d
> gcc bitsort.o -o bitsort -m32 -lphobos -lpthread -lm
> peter@tux ~/D $ ./bitsort
> This is shown.
> Segmentation fault (core dumped)
> peter@tux ~/D $ 
> 
> 
> Is this a bug?
> Peter

In your code. :-) Structs are a value type. Your main() should look like this:

void main() {
    List list;
    list.value = 5;
}

By saying "List* list;" you are declaring a pointer to a list, which is initialized to null. When you then say "list.value", you're dereferencing a null pointer, which causes the segfault.

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://pyd.dsource.org

Kirk McDonald wrote:
> Peter Thomassen wrote:
> 
>> Hi there,
>>
>> I'm coming from PHP and am very new to compiled languages, so maybe I'm
>> completely wrong.
>>
>> I have the following bitsort.d:
>>
>> import std.stdio;
>> struct List {
>>         uint value;
>> }
>> void main() {
>>         List* list;
>>         writefln("This is shown.");
>>         list.value = 5;
>>         writefln("This is not shown.");
>> }
>>
>> And this happens:
>>
>> peter@tux ~/D $ dmd bitsort.d
>> gcc bitsort.o -o bitsort -m32 -lphobos -lpthread -lm
>> peter@tux ~/D $ ./bitsort
>> This is shown.
>> Segmentation fault (core dumped)
>> peter@tux ~/D $
>>
>> Is this a bug?
>> Peter
> 
> 
> In your code. :-) Structs are a value type. Your main() should look like this:
> 
> void main() {
>     List list;
>     list.value = 5;
> }
> 
> By saying "List* list;" you are declaring a pointer to a list, which is initialized to null. When you then say "list.value", you're dereferencing a null pointer, which causes the segfault.
> 


If you want to use a pointer-to-List, assign something to it.

void main() {
    List back;
    List* list = new List;

    //or      List* list = &back;

    list.value = 5;
}