Look at the following source files(main.d and test.d):

// main.d  ----------------------
extern
{
  void MyFunction();
}

void main(char[][] args )
{
  MyFunction();
}


// test.d ----------------------

import std.stdio;

void MyFunction()
{
  writefln("Hello World");
}

compiles fine, but linker complains:
 Error 42: Symbol Undefined _D4main10MyFunctionFZv
--- errorlevel 1


It appears the linker expects the extern function to be in the 'main' module.  This appears to be incorrect behavior.  If it isn't why such a departure from a common C idiom(lex and yacc).

Am I missing something?
-DavidM

On Tue, 13 Jun 2006 23:44:26 +1000, David Medlock <noone@nowhere.com> wrote:

> Look at the following source files(main.d and test.d):
>
> // main.d  ----------------------
> extern
> {
>    void MyFunction();
> }
>
> void main(char[][] args )
> {
>    MyFunction();
> }
>
>
> // test.d ----------------------
>
> import std.stdio;
>
> void MyFunction()
> {
>    writefln("Hello World");
> }
>
> compiles fine, but linker complains:
>   Error 42: Symbol Undefined _D4main10MyFunctionFZv
> --- errorlevel 1
>
>
> It appears the linker expects the extern function to be in the 'main' module.  This appears to be incorrect behavior.

No its not. This is intentional.

> If it isn't why such a departure from a common C idiom(lex and yacc).

Don't know.

> Am I missing something?

Yes. The way to do this is D is that you also create another file 'test.di' that contains ...

 // test.di --------------------
  void MyFunction();

And you modify main.d

 // main.d  ----------------------
 import test;
 void main(char[][] args )
 {
    MyFunction();
 }

Then you compile them as ...

  dmd -c test
  dmd main test.obj

-- 
Derek Parnell
Melbourne, Australia

Derek Parnell wrote:
> On Tue, 13 Jun 2006 23:44:26 +1000, David Medlock <noone@nowhere.com>  wrote:
> 
<snip>
>> Am I missing something?
> 
> 
> Yes. The way to do this is D is that you also create another file  'test.di' that contains ...
> 
>  // test.di --------------------
>   void MyFunction();
> 
> And you modify main.d
> 
>  // main.d  ----------------------
>  import test;
>  void main(char[][] args )
>  {
>     MyFunction();
>  }
> 
> Then you compile them as ...
> 
>   dmd -c test
>   dmd main test.obj
> 

Thanks Derek.

It appears you can also just wrap them both with extern(C) and leave them in D files.

-DavidM

David Medlock wrote:
> Look at the following source files(main.d and test.d):
> 
> // main.d  ----------------------
> extern
> {
>   void MyFunction();
> }
> 
> void main(char[][] args )
> {
>   MyFunction();
> }
> 
> 
> // test.d ----------------------
> 
> import std.stdio;
> 
> void MyFunction()
> {
>   writefln("Hello World");
> }
> 
> compiles fine, but linker complains:
>  Error 42: Symbol Undefined _D4main10MyFunctionFZv
> --- errorlevel 1
> 
> 
> It appears the linker expects the extern function to be in the 'main' module.  This appears to be incorrect behavior.  If it isn't why such a departure from a common C idiom(lex and yacc).
> 
> Am I missing something?

In D the symbol name is based on the module name, which is equivalent to  the file name in the absence of a module statement.  For this reason, "extern (D)" has very limited use.  Generally, I'll only use it if I'm doing something like this:

    extern (C):
    ...
    extern (D) void inlineFunc() {}

Sean