Hi, I'm a new to D and I could not find any relevant answers in the forum.

I want to call functions from D-lib from c++ main.
dlibrary

import std.stdio;

extern (C++) void foo(int i, int j, int k) {
  writefln("i = %s", i);
  writefln("j = %s", j);
  writefln("k = %s", k);
}
void main(){}

######
c++ binary

#include <iostream>

void CXXmain();
void foo(int i, int j, int k);
using namespace std;

int main(){
  cout << "This is the main of C++\n";
  foo(1,3,4);
  return 0;
}

####
I can compile d with dmd and c++ with g++ then linked them with g++.  The problem is when I run the binary I got:

> ./runtest
This is the main of C++
Segmentation Fault

I could not figure out the problem.  And when I call the C++ functions from the main of D everything works.  So why have I segmentation when I call the main from C++.

On Wednesday, 26 June 2013 at 20:19:07 UTC, Milvakili wrote:
> Hi, I'm a new to D and I could not find any relevant answers in the forum.
>
> I want to call functions from D-lib from c++ main.
> dlibrary
>
> import std.stdio;
>
> extern (C++) void foo(int i, int j, int k) {
>   writefln("i = %s", i);
>   writefln("j = %s", j);
>   writefln("k = %s", k);
> }
> void main(){}


Try adding this to D:

extern(C) void initialize_D() {
  import core.runtime;
  Runtime.initialize();
}



And this to C++:

> void foo(int i, int j, int k);

extern "C" void initialize_d();

> using namespace std;
>
> int main(){

    initialize_d();

>   cout << "This is the main of C++\n";
>   foo(1,3,4);
>   return 0;
> }


And you should see something better.

On Wednesday, 26 June 2013 at 20:23:35 UTC, Adam D. Ruppe wrote:
> On Wednesday, 26 June 2013 at 20:19:07 UTC, Milvakili wrote:
>> Hi, I'm a new to D and I could not find any relevant answers in the forum.
>>
>> I want to call functions from D-lib from c++ main.
>> dlibrary
>>
>> import std.stdio;
>>
>> extern (C++) void foo(int i, int j, int k) {
>>  writefln("i = %s", i);
>>  writefln("j = %s", j);
>>  writefln("k = %s", k);
>> }
>> void main(){}
>
>
> Try adding this to D:
>
> extern(C) void initialize_D() {
>   import core.runtime;
>   Runtime.initialize();
> }
>
>
>
> And this to C++:
>
>> void foo(int i, int j, int k);
>
> extern "C" void initialize_d();
>
>> using namespace std;
>>
>> int main(){
>
>     initialize_d();
>
>>  cout << "This is the main of C++\n";
>>  foo(1,3,4);
>>  return 0;
>> }
>
>
> And you should see something better.

That "magically" solves my problem.  Would you mind if I ask you to define what this initialization is all about or guide me to some tutorial related to these issues?

Thanks alot.

On Wed, 26 Jun 2013 22:32:55 +0200, Milvakili wrote:
> That "magically" solves my problem.  Would you mind if I ask you to define what this initialization is all about or guide me to some tutorial related to these issues?
> 
> Thanks alot.

The function initializes the D runtime library.  I believe the initialization must be done primarily due to the garbage collector, but there's a list of what the runtime provides in the readme here: https:// github.com/D-Programming-Language/druntime

On Wednesday, 26 June 2013 at 20:37:25 UTC, Justin Whear wrote:
> On Wed, 26 Jun 2013 22:32:55 +0200, Milvakili wrote:
>> That "magically" solves my problem.  Would you mind if I ask you to
>> define what this initialization is all about or guide me to some
>> tutorial related to these issues?
>> 
>> Thanks alot.
>
> The function initializes the D runtime library.  I believe the
> initialization must be done primarily due to the garbage collector, but
> there's a list of what the runtime provides in the readme here: https://
> github.com/D-Programming-Language/druntime

Great!

I think specifically for writefln it needs to grab module constructors from the initialization, to set up the output stream. The GC and typeinfo would be important for a longer example.

You might also want to do something similar at the end of C++'s main with Runtime.terminate().

On Wednesday, 26 June 2013 at 21:12:26 UTC, Adam D. Ruppe wrote:
> I think specifically for writefln it needs to grab module constructors from the initialization, to set up the output stream. The GC and typeinfo would be important for a longer example.
>
> You might also want to do something similar at the end of C++'s main with Runtime.terminate().

Thanks.

What about the other way around. If I linked them with dmd in that case it throws errors due to <iostream>, what should I do in that case?

On Thursday, 27 June 2013 at 00:00:23 UTC, Milvakili wrote:
> What about the other way around. If I linked them with dmd in that case it throws errors due to <iostream>, what should I do in that case?

I don't think you need to do any special C++ initialization, any needed work there is automatically inserted by the linker.

Just make sure you link with -L-lstdc++ if you're linking with dmd on Linux and the needed c++ lib should be pulled in.

Or if you want to link with g++ or ld, you'll want to link in -lphobos2 to get the D standard library.

Running dmd -v can be helpful to see exactly what is going on:

$ dmd -v test.d
< snip a lot of stuff >
gcc test25.o -o test25 -m32 -L/home/me/d/dmd2/linux/bin32/../lib32 -L/home/me/d/dmd2/linux/bin32/../lib64 -Xlinker --no-warn-search-mismatch -Xlinker --export-dynamic -l:libphobos2.a -lpthread -lm -lrt
$


Right at the end, you can see the command dmd is running to do the link. It uses gcc here, passing a bunch of libraries D will need.



But if you just let dmd do the link you can add C++ libraries with -L-l.