• David Medlock <noone nowhere.com> Jun 13 2006
• "Derek Parnell" <derek psych.ward> Jun 13 2006
• David Medlock <noone nowhere.com> Jun 13 2006
• Sean Kelly <sean f4.ca> Jun 13 2006

David Medlock <noone nowhere.com> writes:

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

"Derek Parnell" <derek psych.ward> writes:

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

David Medlock <noone nowhere.com> writes:

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


 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

Sean Kelly <sean f4.ca> writes:

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