Shared library extern (C) variables

[Jeremy DeHaan]

On Sunday, 5 January 2014 at 19:55:50 UTC, Mineko wrote:
> On Sunday, 5 January 2014 at 19:47:46 UTC, FreeSlave wrote:
>>
>> Some code snippets of what you try to do would help.
>>
>> Maybe this example explain you something:
>>
>> //mod.d
>> extern(C) int foo = 42;
>>
>> void changeFoo(int val)
>> {
>>    foo = val;
>> }
>>
>> //main.d
>> import std.stdio;
>> import mod;
>>
>> int main()
>> {
>>    writeln(foo);
>>    changeFoo(15);
>>    writeln(foo);
>>    return 0;
>> }
>>
>> Compile:
>> dmd -H -c mod.d && //to generate .di file (not required)
>> dmd -shared mod.d -oflibmod.so && //to generate shared library
>> dmd -L-L. -L-lmod -L-rpath=. main.d //rpath is special 
>> argument to linker, so executable will able to find shared 
>> library in its directory. You can omit rpath, but then you 
>> must put your .so file to one of standard directory like 
>> /usr/lib or /usr/local/lib. That's all for Linux. On Windows 
>> you would have different building steps.
>>
>> Also probably you want to make your varialbe __gshared, so it 
>> will not be thread-local. That's default D behavior to make 
>> all global variables thread-local. And I don't know how other 
>> languages will handle D thread-local variable.
>
> Ahh I appreciate it, but I already have that part down and 
> good. :)
>
> I was wondering about how to use export correctly, I apologize 
> for not being clear.
>
> Also I'll keep in mind the __gshared, never even knew about it.

Yeah, the documentation could definitely be better in this 
regard. I don't really have any experience when it comes to 
linking to D shared libraries. All my experience comes from 
linking with C ones.

I might try it out later today just to make sure I have it right, 
but it should be something kind of like this:


libstuff.d

//extern(C) only added because that is what you have been doing
export extern(C) void someFunction(int thing)
{
     //doing stuff with the thing
}

extern(C) void otherFunction(int otherThing)
{
      //stuff with a different thing
}

Assuming libstuff gets put into the shared library


main.d


import libstuff;


void main(sring[] args)
{
      int sweetVariable = 100;
      someFunction(sweetVariable);//should be ok
      otherFunction(sweetVariable);//error, not exported
}


Again, I cannot confirm that this is the exact way to do it, but 
it should be something very similar from what the documentation 
leads me to believe.