Shared library extern (C) variables
Jeremy DeHaan
dehaan.jeremiah at gmail.com
Sun Jan 5 13:00:47 PST 2014
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.
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