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digitalmars.D.learn - Declaring a D pointer to a C function

reply Johannes Pfau <spam example.com> writes:
=46rom a discussion related to derelict:
How do you write this:
-------------------------------------------------------
alias extern(C) int function(void* test) FTInitFunc;
FTInitFunc FT_Init_FreeType
-------------------------------------------------------
without the alias?
-------------------------------------------------------
extern(C) int function(void* test) FT_Init_FreeType;
-------------------------------------------------------
is not the same!
both are fields containing a C function pointer, but the first field
has D name mangling (_D4test16FT_Init_FreeTypePUPvZi) and the second
has C name mangling: (FT_Init_FreeType, which conflicts with the C
function FT_Init_FreeType)

And a related question from stackoverflow:
(http://stackoverflow.com/questions/6257078/casting-clutteractor-to-clutter=
stage)
How to write this:
-------------------------------------------------------
alias extern(C) void function(void*, const char*) setTitleFunc;
auto clutter_stage_set_title =3D
getSym!(setTitleFunc)("clutter_stage_set_title");
-------------------------------------------------------
without the alias?

http://d.puremagic.com/issues/show_bug.cgi?id=3D2168 and
http://d.puremagic.com/issues/show_bug.cgi?id=3D4288 seem to be related,
extern(C) seems to work almost nowhere ;-)


--=20
Johannes Pfau
Jul 12 2011
next sibling parent reply Marco Cosentino <cosentino.ma gmail.com> writes:
On 12/07/2011 11:36, Johannes Pfau wrote:

  From a discussion related to derelict:
 How do you write this:
 -------------------------------------------------------
 alias extern(C) int function(void* test) FTInitFunc;
 FTInitFunc FT_Init_FreeType
 -------------------------------------------------------
 without the alias?
 -------------------------------------------------------
 extern(C) int function(void* test) FT_Init_FreeType;
 -------------------------------------------------------
 is not the same!
 both are fields containing a C function pointer, but the first field
 has D name mangling (_D4test16FT_Init_FreeTypePUPvZi) and the second
 has C name mangling: (FT_Init_FreeType, which conflicts with the C
 function FT_Init_FreeType)

 And a related question from stackoverflow:
 (http://stackoverflow.com/questions/6257078/casting-clutteractor-to-clutterstage)
 How to write this:
 -------------------------------------------------------
 alias extern(C) void function(void*, const char*) setTitleFunc;
 auto clutter_stage_set_title =
 getSym!(setTitleFunc)("clutter_stage_set_title");
 -------------------------------------------------------
 without the alias?

 http://d.puremagic.com/issues/show_bug.cgi?id=2168 and
 http://d.puremagic.com/issues/show_bug.cgi?id=4288 seem to be related,
 extern(C) seems to work almost nowhere ;-)



You should declare the function pointer without the "extern(C)".

Example:
alias int function(void* test) FTInitFunc;

extern(C) int foo(void* test){ .... }

FTInitFunc foo_ptr = &foo;

This worked for me.
Jul 12 2011
parent Marco Cosentino <cosentino.ma gmail.com> writes:
On 12/07/2011 13:15, Trass3r wrote:

 You should declare the function pointer without the "extern(C)".

 Example:
 alias int function(void* test) FTInitFunc;

 extern(C) int foo(void* test){ .... }

 FTInitFunc foo_ptr = &foo;

 This worked for me.



 That's a bug.



Oh, well, I forgot to mention that the function pointer is a callback 
that gets called by a linked C library. IMHO I don't think that the 
alias definition should carry with her the informations about the 
calling convention. This is a convention for the caller and the callee.
Jul 12 2011
prev sibling next sibling parent Trass3r <un known.com> writes:
 You should declare the function pointer without the "extern(C)".

 Example:
 alias int function(void* test) FTInitFunc;

 extern(C) int foo(void* test){ .... }

 FTInitFunc foo_ptr = &foo;

 This worked for me.



That's a bug.
Jul 12 2011
prev sibling next sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 12 Jul 2011 05:36:15 -0400, Johannes Pfau <spam example.com> wrote:


 From a discussion related to derelict:
 How do you write this:
 -------------------------------------------------------
 alias extern(C) int function(void* test) FTInitFunc;
 FTInitFunc FT_Init_FreeType
 -------------------------------------------------------
 without the alias?
 -------------------------------------------------------
 extern(C) int function(void* test) FT_Init_FreeType;
 -------------------------------------------------------
 is not the same!
 both are fields containing a C function pointer, but the first field
 has D name mangling (_D4test16FT_Init_FreeTypePUPvZi) and the second
 has C name mangling: (FT_Init_FreeType, which conflicts with the C
 function FT_Init_FreeType)

 And a related question from stackoverflow:
 (http://stackoverflow.com/questions/6257078/casting-clutteractor-to-clutterstage)
 How to write this:
 -------------------------------------------------------
 alias extern(C) void function(void*, const char*) setTitleFunc;
 auto clutter_stage_set_title =
 getSym!(setTitleFunc)("clutter_stage_set_title");
 -------------------------------------------------------
 without the alias?



extern(C) extern(C) maybe?  :)

or maybe:

extern(C) int function(void * test) extern(C) FT_Init_FreeType;

Just some thoughts, it probably doesn't work.

-Steve
Jul 12 2011
prev sibling next sibling parent Johannes Pfau <spam example.com> writes:
Steven Schveighoffer wrote:

On Tue, 12 Jul 2011 05:36:15 -0400, Johannes Pfau <spam example.com>
wrote:


 From a discussion related to derelict:
 How do you write this:
 -------------------------------------------------------
 alias extern(C) int function(void* test) FTInitFunc;
 FTInitFunc FT_Init_FreeType
 -------------------------------------------------------
 without the alias?
 -------------------------------------------------------
 extern(C) int function(void* test) FT_Init_FreeType;
 -------------------------------------------------------
 is not the same!
 both are fields containing a C function pointer, but the first field
 has D name mangling (_D4test16FT_Init_FreeTypePUPvZi) and the second
 has C name mangling: (FT_Init_FreeType, which conflicts with the C
 function FT_Init_FreeType)

 And a related question from stackoverflow:
 (http://stackoverflow.com/questions/6257078/casting-clutteractor-to-clutterstage)
 How to write this:
 -------------------------------------------------------
 alias extern(C) void function(void*, const char*) setTitleFunc;
 auto clutter_stage_set_title =
 getSym!(setTitleFunc)("clutter_stage_set_title");
 -------------------------------------------------------
 without the alias?



extern(C) extern(C) maybe?  :)

or maybe:

extern(C) int function(void * test) extern(C) FT_Init_FreeType;



Nope, that doesn't work:
---------------------------------
test.d(3): no identifier for declarator int C function(void* test)
test.d(3): semicolon expected, not 'extern'
test.d(3): no identifier for declarator FT_Init_FreeType
---------------------------------

also, if that worked, shouldn't it be equal to this?
---------------------------------
extern(C) int function(void* test) FT_Init_FreeType;
---------------------------------
This works, but it's not what I want.
Derelict needs a _field_, FT_Init_FreeType with D name mangling. So the
usual {module}.{module}.FT_Init_FreeType in mangled form.
This _field_ should contain a pointer to a extern(C) function.

This code with alias does just that:

 -------------------------------------------------------
 alias extern(C) int function(void* test) FTInitFunc;
 FTInitFunc FT_Init_FreeType
 -------------------------------------------------------






functions, so the above must be accomplished without the alias.

I think it should be something like this:
---------------------------------
extern(C) int function(void * test) extern(D) FT_Init_FreeType;
(extern(C) int function(void * test)) FT_Init_FreeType;
extern(C)(int function(void * test)) FT_Init_FreeType;
extern(C){int function(void * test)} FT_Init_FreeType;
---------------------------------
None of these work, though.


Just some thoughts, it probably doesn't work.

-Steve




-- 
Johannes Pfau
Jul 12 2011
prev sibling next sibling parent Johannes Pfau <spam example.com> writes:
Trass3r wrote:

 You should declare the function pointer without the "extern(C)".

 Example:
 alias int function(void* test) FTInitFunc;

 extern(C) int foo(void* test){ .... }

 FTInitFunc foo_ptr = &foo;

 This worked for me.



That's a bug.



I agree. It looks like the above code assigns a extern(C) function
pointer to a field which should only accept D function pointers.
I guess if you then call foo_ptr dmd will use the D calling convention
and that'll crash, at least for more complicated functions.

-- 
Johannes Pfau
Jul 12 2011
prev sibling next sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 12 Jul 2011 09:42:22 -0400, Johannes Pfau <spam example.com> wrote:


 Steven Schveighoffer wrote:

 On Tue, 12 Jul 2011 05:36:15 -0400, Johannes Pfau <spam example.com>
 wrote:


 From a discussion related to derelict:
 How do you write this:
 -------------------------------------------------------
 alias extern(C) int function(void* test) FTInitFunc;
 FTInitFunc FT_Init_FreeType
 -------------------------------------------------------
 without the alias?
 -------------------------------------------------------
 extern(C) int function(void* test) FT_Init_FreeType;
 -------------------------------------------------------
 is not the same!
 both are fields containing a C function pointer, but the first field
 has D name mangling (_D4test16FT_Init_FreeTypePUPvZi) and the second
 has C name mangling: (FT_Init_FreeType, which conflicts with the C
 function FT_Init_FreeType)

 And a related question from stackoverflow:
 (http://stackoverflow.com/questions/6257078/casting-clutteractor-to-clutterstage)
 How to write this:
 -------------------------------------------------------
 alias extern(C) void function(void*, const char*) setTitleFunc;
 auto clutter_stage_set_title =
 getSym!(setTitleFunc)("clutter_stage_set_title");
 -------------------------------------------------------
 without the alias?



 extern(C) extern(C) maybe?  :)

 or maybe:

 extern(C) int function(void * test) extern(C) FT_Init_FreeType;



 Nope, that doesn't work:
 ---------------------------------
 test.d(3): no identifier for declarator int C function(void* test)
 test.d(3): semicolon expected, not 'extern'
 test.d(3): no identifier for declarator FT_Init_FreeType
 ---------------------------------

 also, if that worked, shouldn't it be equal to this?
 ---------------------------------
 extern(C) int function(void* test) FT_Init_FreeType;
 ---------------------------------
 This works, but it's not what I want.
 Derelict needs a _field_, FT_Init_FreeType with D name mangling. So the
 usual {module}.{module}.FT_Init_FreeType in mangled form.
 This _field_ should contain a pointer to a extern(C) function.



Oh, I misread which one did which.  I thought it was the opposite.

Hm... so extern(C) affects both the function pointer type and the name  
mangling.  Interesting.

But wait, don't normal D functions have C calling convention?  I thought  
that was one of the benefits of D's ABI?

-Steve
Jul 12 2011
prev sibling next sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 12 Jul 2011 09:53:28 -0400, Steven Schveighoffer  
<schveiguy yahoo.com> wrote:


 But wait, don't normal D functions have C calling convention?  I thought  
 that was one of the benefits of D's ABI?



Tested it out, definitely is different.  So this clearly needs to be  
addressed.

-Steve
Jul 12 2011
prev sibling next sibling parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
I just had a bug where a D function is implicitly converted to an
extern(C) function pointer.

I've had this definition:
alias extern (C) void function(void* userData) PaStreamFinishedCallback;

And this extern(C) function:
PaError  Pa_SetStreamFinishedCallback(PaStream* stream,
PaStreamFinishedCallback streamFinishedCallback);

And I used this callback:
void StreamFinished(void* userData)
{
    auto localData = cast(TestData*)userData;
    writefln("Stream Completed: %s", localData.message);
}

// this is where the binding takes place
void main() { ...; SetStreamFinishedCallback(..., &StreamFinished); }

That code is invalid. The fix is to add extern(C) to my callback:
extern(C) void StreamFinished(void* userData)

Is this going to be fixed any time soon? Allowing callbacks with D
calling convention where a C callback is expected should be an error,
and this is like the 10th time I've ran into this bug.
Jul 12 2011
parent "Daniel Murphy" <yebblies nospamgmail.com> writes:
"Andrej Mitrovic" <andrej.mitrovich gmail.com> wrote in message 
news:mailman.1569.1310506439.14074.digitalmars-d-learn puremagic.com...

 Is this going to be fixed any time soon? Allowing callbacks with D
 calling convention where a C callback is expected should be an error,
 and this is like the 10th time I've ran into this bug.



What, the bug that annoyed me so much I fixed it myself?  Yeah, this should 
be gone by the next release.
Jul 13 2011
prev sibling next sibling parent Trass3r <un known.com> writes:
 Is this going to be fixed any time soon? Allowing callbacks with D
 calling convention where a C callback is expected should be an error,
 and this is like the 10th time I've ran into this bug.



http://d.puremagic.com/issues/show_bug.cgi?id=3797
Jul 12 2011
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 7/12/11, Trass3r <un known.com> wrote:

 Is this going to be fixed any time soon? Allowing callbacks with D
 calling convention where a C callback is expected should be an error,
 and this is like the 10th time I've ran into this bug.



 http://d.puremagic.com/issues/show_bug.cgi?id=3797
Jul 12 2011
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
Oh there's a pull already, this is great.
https://github.com/D-Programming-Language/dmd/pull/96
Jul 12 2011
prev sibling next sibling parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 7/13/11, Daniel Murphy <yebblies nospamgmail.com> wrote:

 "Andrej Mitrovic" <andrej.mitrovich gmail.com> wrote in message
 news:mailman.1569.1310506439.14074.digitalmars-d-learn puremagic.com...

 Is this going to be fixed any time soon? Allowing callbacks with D
 calling convention where a C callback is expected should be an error,
 and this is like the 10th time I've ran into this bug.



 What, the bug that annoyed me so much I fixed it myself?  Yeah, this should
 be gone by the next release.



Thanks! I've literally lost an entire day once when I was just
starting using D and C together and had a calling convention mismatch.
:x
Jul 13 2011
parent "Daniel Murphy" <yebblies nospamgmail.com> writes:
"Andrej Mitrovic" <andrej.mitrovich gmail.com> wrote in message 
news:mailman.1607.1310570915.14074.digitalmars-d-learn puremagic.com...

 Thanks! I've literally lost an entire day once when I was just
 starting using D and C together and had a calling convention mismatch.
 :x



It's worse than just calling conventions - try changing the parameter types! 
(or basically anything except the return type)
Jul 13 2011
prev sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Wed, 13 Jul 2011 11:32:50 -0400, Daniel Murphy  
<yebblies nospamgmail.com> wrote:


 "Andrej Mitrovic" <andrej.mitrovich gmail.com> wrote in message
 news:mailman.1607.1310570915.14074.digitalmars-d-learn puremagic.com...

 Thanks! I've literally lost an entire day once when I was just
 starting using D and C together and had a calling convention mismatch.
 :x



 It's worse than just calling conventions - try changing the parameter  
 types!
 (or basically anything except the return type)



Yeah, examining the assembly, a major difference is that D passes one  
parameter in a register, whereas C pushes it on the stack.  This means you  
are going to have off-by-one corruption any time you access a parameter.

-Steve
Jul 13 2011